Programming with Visual Basic for Applications - Wiley

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V

isual Basic for Applications (VBA) is a programming language and environment that is included with many Microsoft applications, such as Word, Excel, PowerPoint, and Access. Since Release 14, VBA has been available with AutoCAD as well. VBA is ideally suited for situations in which you need to work with more than one application at a time. ActiveX, which I discussed in the last chapter in relation to Visual LISP, enables you to access objects in other applications. However, you can also use VBA to program AutoCAD alone. This chapter introduces you to VBA and shows how you can start to use this powerful language to customize AutoCAD.

AUTOCAD ONLY

AutoCAD LT does not support VBA. This entire chapter applies to AutoCAD only.

Visual Basic for Applications is a variation of Visual Basic. Visual Basic is not related to any specific application. Visual Basic code is compiled into an executable file that stands alone, unrelated to any specific document. VBA, on the other hand, is connected to its application and the document in which you created the code. VBA provides a simple way to customize AutoCAD, automate tasks, and program applications from within the application. VBA in AutoCAD works slightly differently from VBA in most other applications, in that VBA projects are stored in a separate file, with the DVB filename extension, but can also be stored within the drawing file.

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IN THIS CHAPTER Understanding VBA and AutoCAD Writing VBA code Getting user input Creating dialog boxes Modifying objects Creating loops and conditions Debugging and trapping errors

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Starting to Work with VBA After you decide to program AutoCAD, the first step is to select a programming language to use. VBA has the following advantages: n VBA is faster than AutoLISP, even when AutoLISP is compiled. n VBA is common to many other applications. If you’ve used VBA before, you can easily transfer your knowledge to using VBA in AutoCAD. You’re also more likely to find other programmers who know VBA compared to AutoLISP. n VBA is generally easier to learn than AutoLISP because of its syntax. On the other hand, AutoLISP has the advantage of backward compatibility with prior releases of AutoCAD. Of course, if you’re familiar with AutoLISP but not VBA, it’s hard to beat the ease of working with a language that you already know and use. VBA programs are saved in projects. A project contains all of the parts that are needed to execute the function of the program. You can use the VBA Manager to view your VBA projects. The VBA Manager also enables you to load, unload, save, and create VBA projects. To open the VBA Manager, choose Tools ➪ Macro ➪ VBA Manager.

Opening the VBA environment To start working with VBA, you must open the VBA environment. VBA has its own interface, just like Visual LISP. To open VBA in AutoCAD, choose Tools ➪ Macro ➪ Visual Basic Editor (or type vbaide ↵). Like Visual LISP, VBA has its own interface, called an integrated development environment, or IDE. AutoCAD displays the VBA environment window. VBA projects can contain modules. A module is a self-contained piece of programming code. A VBA project can have one or more modules. To add a module, choose Insert ➪ Module, or click the drop-down list to the right of the second button on the VBA IDE Standard toolbar. Then choose Module. AutoCAD opens a module text editor window so that you can start typing code. In the Project window, VBA adds a new module to the list of modules. By default, the first module is called Module1. Figure 37.1 shows the VBA IDE, including the text editor. If you don’t see the Project Explorer or the Properties window, use the View menu of the VBA IDE to choose Project Explorer or Properties Window. You can resize the module text editor as you would any window. As you start adding code to the text editor, you’ll find it easier to work with a larger window. Click the Maximize button to enlarge the text editor to its maximum size.

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AutoCAD is still running in the background. You can return to it at any time by clicking its button on the Windows task bar, or by clicking View AutoCAD on the VBA IDE Standard toolbar.

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FIGURE 37.1 The VBA environment window.

Getting acquainted with VBA VBA enables you to easily retrieve, create, and manipulate objects. To get a list of objects, open the Object Browser by clicking Object Browser on the Standard toolbar or choosing View ➪ Object Browser. Objects are organized into libraries. All of the objects that you work with in AutoCAD are in the AutoCAD library. To see the list of AutoCAD objects, click the drop-down list and choose AutoCAD. You can see the result in Figure 37.2.

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You can resize the panes in the VBA window. Place the mouse cursor on the bar between the panes until you see the double-headed arrow, and drag it either left or right.

Objects and collections of objects In the left pane, labeled Classes, you see the list of objects. In VBA, you can have both individual objects and collections of objects. For example, AcadLayer would be the layer object, and AcadLayers would be the collection of layers. The purpose of collections is to enable you to work with a group of objects. For example, to add a layer, you add it to the collection of layers; this is because the new layer is not related to any existing layer.

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FIGURE 37.2 You can use the Object Browser to see the AutoCAD library of objects.

Methods and properties What can you do with objects in VBA? First, objects can have properties. For example, you can set an ellipse to the color red because one of the properties of the ellipse object is TrueColor. (Of course, all drawing objects have TrueColor as one of their properties.) Second, objects have methods. A method is an action that you can take on the object. For example, you can delete (erase) an ellipse because Delete is a method of the ellipse object (as well as of all drawing objects). In the Object Browser, the right pane, Members, lists the properties and methods of any object that you choose in the Classes pane.

Investigating the hierarchy model Although you might first think that an object in VBA is the same as an object in an AutoCAD drawing, there is more to the story. In VBA, everything is an object. For example, AutoCAD as an application is an object. Your current drawing is also an object. Model space and paper space are also objects. Therefore, to specify an object in your drawing, you need to specify the application, the drawing, and finally the object in the drawing. To do this, VBA works with a hierarchy of objects. For example, the hierarchy makes it possible to distinguish between an object in your drawing and an object in an Excel spreadsheet. Objects are specified from the most general to the most specific, with a period between each part of the definition. You then add the desired method or properties after another period. For example, you can use the following VBA code to add a circle: Application.ActiveDocument.ModelSpace.AddCircle(center, radius)

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A shortcut for Application.ActiveDocument is ThisDrawing, and so you can also use: ThisDrawing.ModelSpace.AddCircle(center, radius)

In order to work with any object, you need to know where it fits in the hierarchy. The quickest way to see the hierarchical structure from the VBA IDE is to choose any method or property in the Object Browser and to choose Help on the Object Browser’s toolbar. On the Contents tab, choose Object Model to see the listing in Figure 37.3. Within AutoCAD, choose Help ➪ Additional Resources ➪ Developer Help. You’re now in a new Help system. On the Contents tab, double-click ActiveX and VBA Reference. Click Object Model to see the hierarchical model shown in Figure 37.3, or double-click Objects to see the alphabetical object list.

NOTE

FIGURE 37.3 The object model shows you the hierarchy of all of the VBA objects so that you can work with them.

STEPS: Becoming Acquainted with the VBA Environment 1. With any drawing open in AutoCAD, choose Tools ➪ Macro ➪ Visual Basic Editor. AutoCAD opens the VBA IDE. 2. Choose Insert ➪ Module from the menu. The VBA IDE opens the module text editor window. 3. Move down to the Windows task bar and click the AutoCAD button to return to AutoCAD. Now click the Microsoft Visual Basic button to return to the VBA IDE.

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4. Click Object Browser on the VBA IDE Standard toolbar. Click the drop-down list and choose AutoCAD. If necessary, maximize the window by clicking the Maximize button at the top-right corner of the window. 5. In the Classes pane, click AcadLine. You see the associated properties and methods in the right pane. 6. In the right pane, which is labeled Members of AcadLine, click Delete. You see the following at the bottom of the window: Sub Delete() Member of AutoCAD.AcadLine Deletes a specified object Sub indicates the start of a VBA subroutine. Methods are listed in this way.

7. In the right pane, click Layer. At the bottom of the window, you see the following: Property Layer As String Member of AutoCAD.AcadLine Specifies the current layer of the object

8. 9. 10. 11. 12.

This indicates that Layer is a property of AcadLine. String refers to the data type, discussed later in this chapter. Click Help in the Object Browser window. You see the Help page for the Layer property. On the Contents tab, double-click Objects and then click Line object. Scroll down to see all of the properties and methods that belong to the Line object. In the second paragraph of the description, the word AddLine is underlined with a hypertext line. Click it to see the description of the AddLine method. At the top of the page, click Example (also with a hypertext underline). You see an example of VBA code for creating a line. Close Help by clicking the Close button at the top-right corner of each window. Leave the VBA IDE window open if you’re continuing on to the next exercise.

Accessing help VBA offers several help features. You’ve already seen the Object Browser, which provides you with a list of objects as well as their properties and methods. To access help on an object, choose it in Object Browser and click Help. You can do the same for a method or property, as shown in Figure 37.4. After you open a help page, click Example to see an example. These examples are a great way to learn VBA. You can copy a snippet of VBA code and paste it into your own routine, and then edit it as you want. For more general help, AutoCAD offers two systems: n The ActiveX and VBA Reference is an alphabetical listing of objects, methods, properties, and events. n The ActiveX and VBA Developer’s Guide explains ActiveX automation concepts and techniques. To access these reference guides, switch to AutoCAD and choose Help ➪ Additional Resources ➪ Developer Help. The Microsoft Visual Basic for Applications Help provides information on the general VBA environment. Click Help on the VBA IDE Menu Bar toolbar, or choose Help ➪ Microsoft Visual Basic Help. Here you see

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help for other VBA-enabled applications that you may have. You can use this when you’re ready to write VBA code that integrates more than one application. After you start programming, you can get help on any expression by clicking it and pressing F1. For example, you can type AddLine and press F1 to access help on how to create a line. FIGURE 37.4 The help page for the Center Property.

Writing VBA Code Now that you’re familiar with the structure of VBA objects, methods, and properties, you’re ready to start writing some code. As with any programming language, you need to learn syntax and understand variables and when to use them. Luckily, AutoCAD’s VBA Help includes many examples to guide you along the way. After you write some code, you can use it in AutoCAD. Table 37.1 lists the various components of VBA code. This table defines various terms that you can often use when working with VBA.

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TABLE 37.1

Components of VBA Code Term

Definition

Procedure

Code that does something and has a name. A procedure can be a subroutine, a function, or a property.

Project

A set of forms and modules.

Module

A set of subroutines, functions, and declarations that are usually related and comprise a distinct component in a project. A module can contain zero (0) or more procedures (subroutines and functions).

Form

A container for the visual components, such as buttons and text boxes, of a dialog box that you create for your VBA project.

Subroutine

A procedure, written in VBA code, that does not return a value.

Function

A procedure, written in VBA code, that returns a value.

Property

A procedure, written in VBA code, that specifies a value (the property of an object).

Declaration

One or more nonexecutable statements that name constants or variables and define their attributes (such as data type).

Macro

A public subroutine that a user can directly execute.

When you start to create code, VBA can create the basic structure for each procedure for you. With a text or code window displayed, choose Insert ➪ Procedure to open the Add Procedure dialog box shown in Figure 37.5. In the Name text box, type in a name for the new procedure, and then choose the type of procedure that you want to create. Choose whether you want the scope to be Public or Private and then click OK. If a subroutine (called sub for short) is declared Public, it is visible (can be called) from other modules or from the AutoCAD Macros dialog box. A sub that is declared Private is visible only within that module. FIGURE 37.5 The Add Procedure dialog box.

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NOTE

If you check the All Local Variables as Statics check box in the Add Procedure dialog box, your variables retain their values between the times that they’re used.

Looking at VBA syntax To start programming, you need an idea of how a VBA routine is put together. Here is a complete VBA routine that draws a 3D box. ‘Insert a 3D Solid Box Sub Box() ‘declare input variables to AddBox() Dim dOrigin(0 To 2) As Double ‘origin is array of doubles ‘(x,y,z) Dim dLength As Double ‘length Dim dWidth As Double ‘width Dim dHeight As Double ‘height Dim myBox As Acad3DSolid ‘holds return from AddBox() dOrigin(0) = 0# dOrigin(1) = 0# dOrigin(2) = 0#

‘set origin to (0,0,0)

dLength = 5# dWidth = 5# dHeight = 5#

‘make a cube 5 by 5 by 5

‘create the box in modelspace of the current drawing Set myBox = ThisDrawing.ModelSpace.AddBox(dOrigin, dLength, dWidth, dHeight) ‘change the viewpoint to better see the box ThisDrawing.SendCommand (“VPOINT 1,1,1 “) End Sub

Here’s what the code means: n Line 1: Any text starting with an apostrophe (‘) is a comment. Placing comments in your routines helps you and others to understand what you’re doing. n Line 2: Sub indicates the start of a procedure, which is a named, unified piece of code. You can have several subroutines in a VBA project. A project is the file that you save, and it has a DVB filename extension. Each project contains the components of your subroutines, dialog boxes, and so on. The next word is the name of the subroutine. Within the parentheses, you can add arguments, if any. Use an empty set of parentheses if there are no arguments. Declaring variables is discussed later in this chapter. n Line 3: Another comment describing the next few lines of code. It’s always a good idea to comment your code, indicate what is happening, and even write notes to yourself to remind you of your intent. n Line 4: You can also declare variables using the Dim statement. Here dOrigin is used as the variable for the center of the box. (0 To 2) means that the origin will have three parts to it, for the X, Y, and Z coordinates. Double is a type of variable that is suitable for most coordinates. More about variable types later.

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n Lines 5–7: Here you declare the dLength, dWidth, and dHeight variables, which will be used as the length, width, and height of the box. These are declared as type Double, which is also indicated by the d prefix on the variable names. This isn’t required, but it’s a good idea to use a naming scheme for variables to help remind you of their type, especially as you get deeper into programming or have to come back to some code after not seeing it for a while. n Line 8: Here you declare a variable called myBox as an Acad3DSolid to refer to the new box that will be created. Acad3DSolid is a data type that is specific to AutoCAD, and suitable for (you guessed it) referencing a 3D solid in your drawing. You can find other AutoCAD data types by looking in the Object Browser, or by looking at the Object Model as I explained earlier in this chapter. n Lines 9–11: Here you specify the X, Y, and Z coordinates of the origin of the box. The values are assigned to the dOrigin variable. The pound sign (#) is used to indicate a double-precision floating-point value. Use of the # sign is not required here but is more accurate and more clearly indicates your intentions. In some situations, rounding errors can occur when assigning numbers of one type to variables of another type, such as when you assign integers to doubles and doubles to integers. n Lines 12–14: Set the length, width, and height of the box to 5. n Line 15: Another comment. n Line 16: Finally, you’re ready to actually do something. The Set statement is used to set a variable to an object. Here you set the variable myBox to an Acad3DSolid defined by AddBox(dOrigin, dLength, dWidth, dHeight). The AddBox method creates a new 3D box. You need to define its origin, length, width, and height by using the variables that you’ve previously defined. The AddBox method is a member of ModelSpace, which is a member of ThisDrawing. You use ThisDrawing in VBA to access the current drawing. Because VBA within AutoCAD is automatically connected to AutoCAD, you don’t need to specify the application (that is, AutoCAD). n Line 17: Not another comment! Ask yourself these questions: If I looked at this code without the comments, would I have a harder time understanding it? What if there is a bug and I ask another programmer to find it? What if I am that programmer? n Line 18: Here we send the VPOINT command to change the viewpoint. Otherwise, the box that we just created will simply look like a square viewed from the top. The space after the numbers 1,1,1 and before the quotation mark is important; it signifies the end of the command. It’s like pressing the Enter key for this command. Line 19: End Sub ends the subroutine. n To find the syntax for a statement that you want to use, look in VBA Help, as explained in the “Accessing help” section earlier in this chapter. In the preceding VBA routine, you might want to click AddBox and press F1 to find the syntax and elements that are required for creating a box. Then click Example to see an actual example of code for that statement.

Saving a VBA routine As I mention earlier, the AutoCAD version of VBA saves VBA projects as separate files with a DVB file name extension. However, when you run a routine, AutoCAD lists it in the format ModuleName:Procedure Name. If your project has only one module, you can give the module and the procedure the same name. However, most VBA routines have more than one module, with one module controlling the rest. By running the controlling module, you run the whole project.

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To name a module, look in the Properties window. After you’ve created a module, the VBA IDE lists its name property as Module1 by default. Double-click Module1 and type a new name. Notice that the module name in the Project window also changes accordingly.

NOTE

A module name (as well as the names of other forms and controls) must start with a letter and can be up to 31 characters. Only letters, numbers, and the underscore character are allowed.

To save a project as a separate file, which includes all of the modules, click Save on the VBA IDE Standard toolbar. VBA returns you to AutoCAD and opens the Save As dialog box. Type a name for your project, choose a location, and click Save. You can save your project in the Sample\VBA subfolder in the AutoCAD 2008 folder, or use another folder that is in AutoCAD’s support file search path.

Loading a VBA routine Before you run a VBA routine, it must be loaded. If you’re working on the routine and want to run it to check how it works — which you’ll do often — you don’t need to load the routine. However, if you want to run a routine that hasn’t been loaded, you need to use the VBALOAD command. When you choose Tools ➪ Macro ➪ Load Project (or type vbaload ↵), AutoCAD opens the Open VBA Project dialog box. Navigate to your project, choose it, and click Open. (AutoCAD asks you to confirm that you want to enable macros.) The project is now loaded.

Running a VBA routine After you complete a subroutine, you can run it in AutoCAD. After all, that’s the reason for writing VBA code in the first place. To run a VBA routine, choose Tools ➪ Macro ➪ Macros (or type vbarun ↵). In the Macros dialog box, choose the module that you want to run and click Run. AutoCAD runs the module, including other modules that may be controlled by the module that you run.

Using the Visual Basic Editor When you type code from scratch in the Visual Basic Editor, you immediately notice that Visual Basic colorcodes your text as you go. The most common colors are: Normal text Syntax-error text Comments Keyword text

Black Red Green Blue

Keywords include variable types and other words that Visual Basic recognizes, such as Dim and Sub.

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You can customize these colors by choosing Tools ➪ Options from the Visual Basic menu and then choosing the Editor Format tab. Choose a type of text and then choose the desired color.

Click OK.

When you start to type a keyword that Visual Basic recognizes, you’ll often see a box pop up that enables you to choose from a list, or that helps you to complete the word. The editor also adds or removes spaces and capitalizes certain words for you to improve your syntax. If you make a syntax mistake, a small error message often appears as you work. In these ways, the Visual Basic Editor helps you to type accurate code.

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STEPS: Creating, Saving, and Running a VBA Program 1. Start a new drawing using the acad.dwt template. Choose Tools ➪ Macro ➪ Visual Basic Editor. 2. Choose Insert ➪ Module. VBA opens the module text editor. (If you’ve previously opened a module, Visual Basic may launch with a blank module already open. In that case, skip this step.) 3. Choose Insert ➪ Procedure. In the Name text box, type DrawTorus. The type should be Sub and the scope should be Public. Click OK. 4. Type the following code. (Note that the second and last lines are already there for you.) ‘insert a Torus Public Sub DrawTorus() ‘declare variables Dim dCenter(0 To 2) As Double Dim dRadius1 As Double Dim dRadius2 As Double Dim myTorus As Acad3DSolid ‘set center of torus to 0,0,0 dCenter(0) = 0# dCenter(1) = 0# dCenter(2) = 0# dRadius1 = 10# dRadius2 = 2#

‘torus radius ‘tube radius

‘insert the torus Set myTorus = ThisDrawing.ModelSpace.AddTorus(dCenter, dRadius1, dRadius2) ‘set the viewpoint and shade it ThisDrawing.SendCommand (“VPOINT 1,1,1 VSCURRENT CONCEPTUAL “) End Sub

5. In the Properties window, change the name of the module to DrawTorus. 6. Because this routine is active, you don’t need to load it. Choose Save on the VBA IDE Standard toolbar. Save the project as ab37-01.dvb in your AutoCAD Bible folder. 7. Use the Windows task bar to return to your drawing. Choose Tools ➪ Macro ➪ Macros. In the Macros dialog box, choose DrawTorus and click Run. VBA draws and shades the torus.

Don’t save your drawing. Here’s an explanation of the routine that you just wrote and used. Note that blank lines are ignored. Line 1: Comment describing routine. Line 2: This is a public subroutine named DrawTorus with no parameters. Line 3: Comment indicating which variable declarations are next. Line 4: Declare the array to hold the X, Y, and Z coordinates for the center of the torus. Line 5: Declare the variable to hold the radius of the torus. n Line 6: Declare the variable to hold the radius of the tube. n Line 7: Declare the variable to hold the created 3D object. n n n n n

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Line 8: Comment. Lines 9–11: Set the center to 0,0,0. Line 12: Set the torus radius to 10.0. Line 13: Set the tube radius to 2.0. Line 14: Comment. Line 15: Create the torus. Line 16: Comment. Line 17: Send commands to AutoCAD to set the viewpoint and set the visual style to Conceptual for better viewing. Line 18: End of subroutine. n n n n n n n n n

Understanding variables A variable holds a value for later use in your program. In VBA, you don’t need to explicitly declare your variables in advance (as long as you don’t include Option Explicit, which I explain later). You use the Set statement to set a variable to an object, as in the example here. This statement creates a variable, cir, and sets its value equal to the circle that the AddCircle method creates. Set cir = ThisDrawing.ModelSpace.AddCircle(cen, radius)

When you create a variable in this way, VBA assigns the default variant type to it. The variant type of variable can contain numbers, dates, or strings (of text). However, declaring variables explicitly in advance has two advantages: n You can specify the type of variable, which usually uses less memory than the default variant type. n As you continue to enter code, VBA checks the variable’s spelling for you, thus reducing the chance for errors. You declare variables using the Dim statement. Here’s an example: Dim radius As Double

You can create three different levels of variables: n A Public variable is available to all procedures in the project. It is shown as follows: Public dRadius As Double

n A module-level variable is available to all of the procedures in the module. You create a modulelevel variable by placing the declaration (with the Dim statement) at the top of a module, in a Declarations section. Another way to create a module-level variable is to use the Private statement. Examples are shown here: Dim dNum3 as Double Private dNum2 as Double

n A procedure-level variable is used only within a procedure. You can place the variable anywhere within the procedure, as long as you declare the variable before you use it. Placing the statement Option Explicit in a Declarations section requires all variables to be declared. Using Option Explicit is a way to force yourself to write your code more carefully. Declared variables are easier to debug because they’re easier to find.

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Table 37.2 describes the kinds of variables that you can declare. TABLE 37.2

VBA Variable Types Variable

Description

Boolean

For variables that can have only two values — True or False.

Byte

Positive integers from 0 to 255.

Integer

Integers from –32,768 to +32,767.

Long

Integers from –2,147,483,648 to +2,147,483,647.

Currency

Values from –922,337,203,685,477.5808 to +922,337,203,685,477.5807. Use this variable for currency or for other values that need accuracy to several decimals.

Single

Single-precision floating-point values. Single variables use less memory than double variables, but their values are limited.

Double

Double-precision floating-point values. Double variables offer much greater precision than single variables. Most coordinates use this variable type. Three double variables create the X, Y, and Z values.

Date

Holds dates and times that are stored as real numbers. The number to the left of the decimal is the date, and the number to the right of the decimal is the time.

String

Fixed- or variable-length text strings, including letters, numbers, spaces, and punctuation characters.

Object

Objects such as an application, a drawing, or a drawing object.

Variant

Contains numbers, dates, or strings. When you don’t declare a type for a variable, VBA uses this type by default.

Here’s an example that uses the Date variable type and displays it in a message box: Sub DateDemo() Dim dt As Date Dim dbl As Double dt = Now ‘set the dt to the current date and time dbl = dt ‘assign this date value to a double MsgBox “Normal date version: “ & dt & “ Double version: “ & dbl End Sub

Running DateDemo (by pressing F5) would show something similar to: Normal date version: 5/10/2005 8:03:13 PM Double version: 38482.8355671296

Creating VBA statements Although a complete discussion of how to write VBA code is beyond the scope of this book, some general principles will be helpful.

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A statement in VBA is the most basic unit of code. It contains a complete instruction. There are three kinds of statements: n A declaration names a variable, constant, or procedure, as in this example: Dim dOrigin as Double

n An assignment assigns a value to a variable or constant. For example: dOrigin = 0#

n An executable creates an action. For example, it can execute a method or function, or create a loop or branch that acts on a block of code, as shown here: Set myBox = ThisDrawing.ModelSpace.AddBox(dOrigin, dLength, dWidth, dHeight)

VBA has many keywords, functions, and other components that you can use to create code. To find the basic components of the VBA language, choose Help ➪ Microsoft Visual Basic Help. From the Contents tab, double-click Visual Basic Language Reference, which lists terms that are part and parcel of VBA. Here are some examples: n Constants: Constants can be used anywhere in your code to provide a named value. For example, VBA offers color and date constants that you can use to specify colors and dates. n Functions: VBA includes many functions that you’ll find familiar if you’ve used AutoLISP. For example, the ABS function returns the absolute value (without a plus or minus sign) of any number. The DATE function returns the current system date. n Keywords: Keywords are words that have a special meaning in VBA. They are often used as parts of VBA statements. For example, Else is a keyword that is used in the If...Then...Else statement. You’re already familiar with the Set keyword, which is used in the Set statement. n Operators: VBA includes all of the usual arithmetic operations, such as +, –, *, /, and ^. You can also use & to concatenate text strings. There are several logical operators, such as and, not, and or. n Statements: Statements help you to create the flow of your code. You’re already familiar with the Set statement. Other statements are For Each...Next and If...Then...Else. These provide looping capabilities in VBA. Remember that you can also find a list of objects and their properties and methods in the Object Browser, as I explained earlier in this chapter.

Getting User Input The examples shown in this chapter weren’t very useful, partly because the routines provided no way to get user input for the properties of the objects that they drew. There are two main ways to get user input: on the command line and through a dialog box. In this section, I explain how to get user input on the command line. In order to use the user-input methods, you need to first use something called the Utility object. The Utility object belongs to the Document object and controls the methods that get user input. You can also use ThisDrawing, as in the following example. Dim iReturn as Integer iReturn = ThisDrawing.Utility.GetInteger(“Enter an integer: “)

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Here you set a variable called iReturn that is equal to the integer that the user types on the command line. The prompt is Enter an integer:. You can use this type of user input to get a pick point, a numeric value (such as the radius of a circle), a text string, or an object. Use this method when the input is short and sweet. To avoid several prompts appearing on the same line, use vbCrLf, the carriage return/linefeed constant, at the beginning of a prompt, as in the following example: prompt1 = vbCrLf & “Specify center point: “

Here’s an example that illustrates how to get user input on the command line: Sub AddCircle() Dim thePt As Variant Dim theRadius As Double Dim myCircle As AcadCircle thePt = ThisDrawing.Utility.GetPoint(, vbCrLf & “Enter Center Point:”) theRadius = ThisDrawing.Utility.GetReal(“Enter radius: “) Set myCircle = ThisDrawing.ModelSpace.AddCircle(thePt, theRadius) End Sub

Table 37.3 lists some commonly used methods for getting user input. If you know the GET functions in AutoLISP, you’ll be familiar with these methods. TABLE 37.3

Common User-Input Methods Method

Syntax

Description

GetEntity

GetEntity Object, PickedPoint, Prompt

The user selects an object (entity) by picking it. Returns the object in the first parameter and the point picked in the second parameter. The prompt is optional. Example: ThisDrawing.Utility.GetEntity getObj, basePnt, “Select an object” where getObj has been declared as an Object type variable.

GetInteger

RetVal = GetInteger (Prompt)

Any integer from –32,768 to +32,767 is valid. The prompt is optional. Example: getInt = ThisDrawing.Utility.GetInteger(“Ente r an integer: “)

GetPoint

RetVal = GetPoint (Point, Prompt)

Returns a variant (which contains a three-element array of doubles). The user can pick a point, or type in a coordinate. If the Point parameter (optional) is provided, AutoCAD draws a rubber band line from Point to the current crosshair position. The prompt is also optional. Example: getPnt = ThisDrawing. Utility.GetPoint(, “Specify a point: “)

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Method

Syntax

Description

GetReal

RetVal = GetReal (Prompt)

Gets any real (positive or negative) number. The prompt is optional. Example: getaReal = ThisDrawing.Utility.GetReal(“Enter a real number: “)

GetString

RetVal = GetString (HasSpaces, Prompt)

The HasSpaces parameter specifies whether the string can contain spaces. If the HasSpaces parameter is TRUE, the string can contain blanks and the user must press Enter to end input. If HasSpaces is FALSE, either entering a blank or pressing Enter ends input. The prompt is optional. Example: getaString = ThisDrawing. Utility.GetString(False, “Enter text (a space or terminates input):”)

STEPS: Creating a VBA Routine That Gets User Input 1. Start a new AutoCAD drawing using the acad.dwt template. 2. To start a new project, choose Tools ➪ Macro ➪ VBA Manager. Click New and then click Visual Basic Editor. 3. Choose Insert ➪ Module and then choose Insert ➪ Procedure. Name it HappyFace and click OK. 4. At the cursor, type the following: Dim prompt As String, prompt2 As String Dim cen As Variant Dim rad As Double Dim cir As AcadCircle Dim arc As AcadArc Dim pi As Double Dim dStart As Double ‘start angle Dim dEnd As Double ‘end angle pi = 3.1415 prompt = vbCrLf & “Specify center point: “ prompt2 = vbCrLf & “Specify radius: “ ‘get center point from user cen = ThisDrawing.Utility.GetPoint(, prompt) rad = ThisDrawing.Utility.GetDistance(cen, prompt2) ‘draw head Set cir = ThisDrawing.ModelSpace.AddCircle(cen, rad) ‘draw smile dStart = 225 * pi / 180 ‘pi / 180 converts to radians DEnd = 315 * pi / 180

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Set arc = ThisDrawing.ModelSpace.AddArc(cen, rad / 2, dStart, dEnd) ‘draw eyes cen(0) = cen(0) - rad / 4 cen(1) = cen(1) + rad / 4 Set cir = ThisDrawing.ModelSpace.AddCircle(cen, rad / 8) cen(0) = cen(0) + rad / 2 Set cir = ThisDrawing.ModelSpace.AddCircle(cen, rad / 8)

5. Change the module name to HappyFace. 6. Choose Save from the VBA IDE Standard toolbar, and save the VBA project as ab37-02.dvb in your AutoCAD Bible folder. 7. Return to your drawing and choose Tools ➪ Macro ➪ Macros. In the Macros dialog box, choose HappyFace and click Run. 8. Respond to the prompts. HappyFace draws the circle with the center point and radius that you specify.

You don’t need to save your drawing. The previous example uses GetDistance rather than GetReal to enable the user to select the radius of the circle with the mouse. The center point that you previously selected feeds into the GetDistance function. Also, there are calculations to convert degrees to radians. The location and size of the eyes and smile are relative to the center and radius.

Creating Dialog Boxes One of the main characteristics of VBA is the ease with which you can create dialog boxes to get user input. Whenever you need input that is more complex than you can get using the Get methods, you should use a dialog box. You can also use a dialog box to create a more professional look or for ease of use. When working with a dialog box, you generally create the dialog box first and then attach code to the dialog box buttons. You then use a second module to display the dialog box. Running the second module then controls the entire routine. In VBA, a dialog box is called a user form. To create one, choose Insert ➪ UserForm. VBA creates a blank user form that will become your dialog box. Simultaneously, the Toolbox toolbar appears. If this toolbar covers up some other part of your screen, drag it to one side. Your screen should look like Figure 37.6.

Understanding the Toolbox toolbar The Toolbox toolbar contains the tools that you need to create a dialog box. These are the familiar controls that you see in the dialog boxes that you use all the time, such as text boxes, list boxes, check boxes, and so on. Table 37.4 explains the Toolbox toolbar buttons. If you think that the Toolbox toolbar has a lot of possibilities, right-click the Toolbox toolbar and choose Additional Controls. From the Additional Controls dialog box, you can choose from many more controls.

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FIGURE 37.6 The VBA IDE with a blank user form and the Toolbox toolbar.

TABLE 37.4

The Toolbox Toolbar Buttons Button

Description

Select Objects

Enables the user to select objects

Label

Creates a label on the dialog box

TextBox

Enables the user to type in text

ComboBox

Combines features of text and list boxes

ListBox

Enables the user to choose from a list

CheckBox

Creates a box that can be checked or unchecked

continued

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TABLE 37.4 Button

(continued) Description

OptionButton

Enables the user to choose one option from several possibilities (also called a radio button)

ToggleButton

Creates an on/off switch

Frame

Creates a box around a section of the dialog box

CommandButton

Creates a button that executes a command, such as OK and Cancel buttons

TabStrip

Creates tabs along the top of the dialog box

MultiPage

Creates multiple pages

ScrollBar

Creates a scroll bar

SpinButton

Enables the user to specify a number

Image

Inserts an image

Changing dialog box properties After you insert a user form, you should name it. Find the Name property in the Properties window, and change it from UserForm1 (the default name) to any useful name that you want. You might find it useful to use the word frm in the name. For example, for a routine to draw a circle, you could call the user form frmCircle. Figure 37.7 shows the property box when you insert a user form. You can easily change the dialog box’s properties in the property box. One property that you’ll want to change is the Caption property of the dialog box. The dialog box should have a caption that summarizes its purpose. When you type the new caption in the property box, the caption on the dialog box changes at the same time.

Adding dialog box controls One of the more commonly used controls is the command button. A command button is a button that you click in the dialog box to execute an action. The most familiar command buttons are the OK and Cancel buttons.

Add a command button To add a command button, click CommandButton on the Toolbox toolbar. Move your cursor over the dialog box, and drag to create a button. Figure 37.8 shows a dialog box with a new command button. The selection border and handles indicate that the button is a selected object. You can move the button by dragging it. You can resize the button by dragging one of the handles. Add all of the command buttons that you need. Don’t forget to include at least a Cancel button. Many dialog boxes also have an OK button. If you know in advance all of the controls that you’ll need, you can add them all at once. There’s an art to laying out a dialog box so that it’s clear and easy to understand. After a while, you’ll get the hang of it. Pay more attention to the dialog boxes that you use every day to pick up some design pointers.

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FIGURE 37.7 When you insert a user form (dialog box), the Properties window lists all of its properties.

FIGURE 37.8 A dialog box with one selected command button.

Just as the dialog box has properties, each control on the dialog box has properties. When a control such as a command button is selected, you see its properties in the Properties window. You generally would change at least the caption and the name of a command button. It’s a good idea to change the names to something meaningful, rather than using the default name. For example, instead of CommandButton1, use a name such as cmdDrawBox or cmdOk.

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Getting User Input for a Circle Radius

H

ere’s another example of a routine that draws a circle, although here you get user input for the radius using the VAL function. The VAL function returns a numerical value from a text string. Here you create a text box that enables users to type in a radius. The VAL function converts the string in the text box to a number and uses it as the circle’s radius. Follow these steps: 1. Open AutoCAD with a new drawing, using the acad.dwt template. Open the VBA IDE. 2. Choose Insert ➪ UserForm. 3. In the Properties window, change the name of the form to frmDrawCircle, and the caption to Draw a Circle Demo. 4. From the Toolbox toolbar, choose Label and drag a small rectangle on the left side of the form, around the middle. 5. Change the name to lblRadius and the caption to Radius. 6. Choose Textbox on the Toolbox toolbar, and drag a box on the form to the right of the label. 7. Change the name to txtRadius. 8. Choose CommandButton on the Toolbox toolbar, and drag a larger box at the top-center of the form. 9. Change the name to cmdDrawCircle and the caption to Draw Circle. 10. Double-click this command button to bring up the code editor in the cmdDrawCircle_Click () subroutine. 11. Add the following lines: Dim dCenter(0 To 2) As Double Dim dRadius As Double Dim myCircle as AcadCircle dCenter(0) = 0# dCenter(1) = 0# dCenter(2) = 0# dRadius = Val(txtRadius) Set myCircle = ThisDrawing.ModelSpace.AddCircle(dCenter, dRadius) myCircle.Update 12. Close the code window. Save the routine if you want. On the VBA IDE menu, choose Run ➪ Run Sub/UserForm. Visual Basic returns you to your drawing and displays the dialog box. Enter a number for the radius and click the Draw Circle command button. 13. Add as many circles as you like. Click the Close box of the dialog box when you’re done.

Write the VBA Code for a command button After you create a command button, you can attach VBA code to it. To attach VBA code to a control, double-click the control. The text editor opens with the Sub and End Sub lines already entered for you. Type the code that you want to attach to the button.

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VBA dialog boxes are modal by default, which means that they must be closed before AutoCAD can do anything further. To close a dialog box after your VBA code has run, use Unload Me at the end of a routine. To run VBA code that is attached to a dialog box, you need to show the dialog box so that you can use it — click a command button, type in text, and so on. The VBA IDE creates private subroutines for each dialog box control. To show the dialog box, start a new module and create code that looks like the code in this example: Sub DrawArc() frmArc.Show End Sub FrmArc is the name of the user form in this example. Don’t forget to name the user form in the Properties window. Also, remember to name the module, because the module name is what appears in the Macro dialog box when you want to run the routine.

Add a label A command button is quite simple. You just click it, and it performs. You can label its function right on the command button. However, most other controls require some more explanation. For example, if you want the user to type in text, you need a text box. However, a text box has no caption. Therefore, you need to add instructions to the user. A dialog box may also need other instructions to clarify the purpose of the controls, which responses are required, and so on. You add instructions with the Label tool on the Toolbox toolbar. Click Label and drag a rectangle on your dialog box. Then type the label. You can resize or move the label as needed.

Add other dialog box controls The code for some of the dialog box controls can be quite complex. For example, to create a list box that enables the user to choose from an existing list of options, you’d probably create the list of options in advance. For help on creating dialog boxes, choose Help ➪ Microsoft Visual Basic Help. On the Contents tab, double-click Microsoft Forms Reference, and then Microsoft Forms Object Model Reference. From there, you may want to double-click Objects, Collections, and Controls. You can double-click a control, such as the ListBox control, and then read more about it. The specific controls also offer hyperlinks to examples that you can look at.

STEPS: Creating a Dialog Box with a Command Button 1. Start a new drawing in AutoCAD using the acad.dwt template. 2. To start a new project, choose Tools ➪ Macro ➪ VBA Manager. Click New and then click Visual Basic Editor. 3. Choose Insert ➪ UserForm. If the Toolbox toolbar covers the user form or project window, drag it to the right. 4. With the user form active (click its title bar to make it active), change the Name property of the user form to frmArc in the Properties window. 5. Change the Caption property of the user form to Draw an Arc. Watch the caption of the user form change as you type. 6. Choose CommandButton on the Toolbox toolbar. (It’s the last button in the second row. If you don’t see the Toolbox toolbar, click in the user form on the right side of your screen.) Move the cursor over the user form and drag to create a wide button across the upper center of the user form.

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7. Change the Caption property of the button to Draw the Arc!. Change the Name property to cmdDrawArc. 8. Again, choose CommandButton on the Toolbox toolbar. Create a smaller button below the first one near the right side of the user form. 9. Change the Caption property of the smaller button to Cancel. Change its Name property to cmdCancel. Your dialog box should look like the one in Figure 37.9.

FIGURE 37.9 A simple dialog box created in VBA.

10. Double-click the larger button. In the text editor, type the following code at the cursor’s current location between the Private Sub and End Sub statements: ‘declare variables Dim startang As Double Dim endang As Double Dim ctr(0 To 2) As Double Dim rad As Double Dim newarc As Object ‘specify arc parameters startang = 0 ‘angles are in radians. endang = 100 ctr(0) = 5 ctr(1) = 2 ctr(2) = 0 rad = 2 ‘draw arc Set newarc = ThisDrawing.ModelSpace.AddArc(ctr, rad, startang, endang) ‘close dialog box Unload Me 11. From the left (Object) drop-down list at the top of the text editor, choose cmdCancel to add the code for the second button. In the space below the start of the subroutine (Private Sub cmdCancel_Click()), type Unload Me.

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12. Choose Insert ➪ Module. In the new text editor, type the following to display the dialog box. Sub DrawArc() frmArc.Show

Visual Basic places the End Sub statement for you after the code. 13. In the Properties window, change the module’s name to DrawArc. 14. Click Save on the toolbar and save the file in your AutoCAD Bible folder as ab37-03.dvb. 15. Return to your drawing. Choose Tools ➪ Macro ➪ Macros. In the Macros dialog box, choose DrawArc and click Run. 16. Click the large button. AutoCAD draws the arc.

Modifying Objects Modifying objects is usually very easy. You need to know the name of the object. If you’ve created it, you set it equal to a variable, and then you can use that variable. If you’ve created a circle named cir1, the following code changes its layer to “fixtures”, assuming that “fixtures” exists: Cir1.layer = “fixtures”

To add a layer, use the Add method of the Layers collection of objects: Set Newlayer1 = ThisDrawing.Layers.Add(“fixtures”)

You can then set the layer’s properties. For example, the following code makes the layer not plottable. Newlayer1.Plottable = False

The UPDATE command forces the changes to the current view. It updates the change to the screen so that you can see it. For example, you can create a circle with the following code: Set myCircle = ThisDrawing.ModelSpace.AddCircle(dCenter, cRadius)

This adds the circle to the current drawing’s database, but has not yet updated the view. If you do this from a dialog box, the view will not be updated until you exit the dialog box, unless you force an update with the following code: myCircle.Update

Using constants Constants are names that are given to commonly used values. For instance, AutoCAD defines constants for the seven standard colors: acRed, acYellow, acGreen, acCyan, acBlue, acMagenta, and acWhite. In the DrawCircle example, after creating the circle, you could add the following code to change its color to blue: Dim clrObj As AcadAcCmColor Set clrObj = myCircle.TrueColor clrObj.ColorMethod = acColorMethodByACI clrObj.ColorIndex = acBlue myCircle.TrueColor = clrObj

Most functions or properties that have a standard set of values will have corresponding constants defined.

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Accessing Other Applications

T

he true power of VBA comes when you can integrate other applications into your work. For the most part, accessing other applications is beyond the scope of this book, but here are a couple of simple examples that you may find helpful to explain the process.

The technology that enables two applications or components to communicate with each other is called automation. Automation requires a client and a server. The server is the application or component that provides services to the client. The client is the application that makes use of these services. Many applications can perform as both Automation clients and Automation servers, including AutoCAD, Access, Excel, and Word. Most ActiveX controls are Automation servers. Any application that supports VBA can be an Automation client. In order for a client to properly communicate with a server, it must properly use the server’s object model or hierarchy. (The AutoCAD object hierarchy was discussed earlier in this chapter.) You can view a server’s object model or hierarchy using the Object Browser. Most components have a Type Library file (most have a TLB or OLB filename extension) that can be imported from the Tools ➪ References menu in the VBA IDE. If the server is in the current list, make sure that it’s checked. If it isn’t in the list, click Browse, locate its TLB file, and click Open. This will add it to the list of references and make it available to the Object Browser. There are two approaches for creating instances of automation component objects: early binding and late binding. With early binding, you use the VBA keyword New to reference the components type library at design time. With late binding, you declare a variable using the Object data type, and later use CreateObject or GetObject to create the specified type at runtime. Early binding offers several benefits over late binding, including speed, syntax checking in the VBA editor, and online help. Some automation components do not support early binding. Here are two Excel examples, one using early binding and the other using late binding:

Sub XlsEarly() Dim objXls As New Excel.Application ‘Note that the application is not launched until a property or method is referenced MsgBox “Application: “ & objXls.Name & “ Version: “ & objXls.Version objXls.Visible = True objXls.Quit Set objXls = Nothing End Sub Sub XlsLate() Dim objXls As Object ‘CreateObject will launch the application Set objXls = CreateObject(“Excel.Application”) MsgBox “Application: “ & objXls.Name & “ Version: “ & objXls.Version objXls.Visible = True objXls.Quit Set objXls = Nothing End Sub

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Using functions Functions are a type of procedure (like subroutines), except that they return a value. Here’s an example for those of you who are counting the days until January 1, 2008. (If you’re reading this after that date, you can change it to a later date.) Alternatively, it will tell you how many days ago January 1, 2008 occurred (indicated by a negative value). Function DaysTil2008() As Integer ‘the return type of Dim dtToday As Date Dim dt2008 As Date

‘notice “As Integer” tells ‘the function ‘holds today’s date ‘holds Jan 1, 2008

dtToday = Now() dt2008 = CDate(“1/1/2008”) DaysTil2008 = dt2008 - dtToday ‘return value assigned End Function

‘assign today’s date ‘assign Jan 1, 2008 ‘calculate difference, ‘to function name ‘same as End Sub

To use this function, you must do something with the return value through an assignment, or use it as a parameter to another procedure. For example: Public Sub Test2008() MsgBox “Days until year 2008: “ & DaysTil2008() End Sub

You can then run the Test2008 sub to open a message box that tells you how many days are left until the year 2008.

Debugging and Trapping Errors As with all programming languages, there are techniques to help you find the errors that inevitably crop up. Here is a simple debugging technique to get you started: 1. Go to the code editor and to the procedure where you suspect the error resides. 2. Place the cursor on the first executable statement in the procedure, and choose Debug ➪ Toggle Breakpoint (or press F9). 3. Begin stepping through each statement by pressing F8 (Step Into). 4. For simple variables (Integers, Doubles, and Strings), you can place the mouse cursor over the variable, and it will display the current contents. You can also add variables to the Watch window (choose View ➪ Watch Window) or enter commands in the Immediate window (choose View ➪ Immediate Window) to verify your logic. 5. When an error is located, choose Run ➪ Reset and make the correction. You can also use Reset at any time you want to halt the routine. 6. The next time you run the procedure, your breakpoint is still set. At this point, you can either step through again and verify whether your changes are correct, or press F9 to toggle the breakpoint off and choose Run ➪ Run to run the routine normally.

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Unexpected errors may occur. For example, a file that you attempt to open may not exist, your system may run out of memory and not be able to insert that AutoCAD block into your drawing, or you may unintentionally write a routine that divides by 0. You can, and should, plan for some of these errors; for others, it may not be possible to do so. VBA provides a mechanism for catching errors and handling them gracefully, rather than burping all over your screen or locking up your system. A simple framework to begin error trapping would be: Sub MyRoutine() ‘declare variables ... On Error GoTo ErrorHandler ‘rest of procedure goes here Exit Sub ‘Tells subroutine to exit ignoring the ‘ErrorHandler statements ErrorHandler: MsgBox “Error “ & Err.Number & “ “ & Err.Description Resume Next End Sub

This simple error trapping will at least alert you to any errors that occur by providing an error number and description. This will give you the opportunity to begin handling specific errors appropriately as required. The Active X and VBA Developer’s Guide has a good discussion on handling errors in the “Developing Applications with VBA” section.

Moving to Advanced Programming The chapters in this part have reviewed the fundamentals of Visual LISP and VBA, and you’ve seen the power that these languages provide for automating your work. However, they are not the only options for programming AutoCAD. ObjectARX applications share the same memory space as AutoCAD, and are many times faster than routines written in AutoLISP or VBA. ObjectARX is based on C++ and enables full object-oriented interfacing with AutoCAD. An object-oriented interface enables the programmer to create an object in memory (such as an arc), modify its attributes, and then modify the AutoCAD database. You can create custom objects that inherit properties from AutoCAD objects; that is, your object can assume all of the properties of a given object that is already in AutoCAD, and you can add to it. For example, you can inherit from a line so that your custom object has everything that the line does, and then you can add width to it if you want. ObjectARX offers a variety of tools that are unavailable to AutoLISP programmers; however, ObjectARX involves much greater development time than AutoLISP. You can use managed wrapper classes within ObjectARX to create .NET applications as well. AutoCAD 2008 requires the Visual C++ 2005 (version 8.0) compiler to compile and link applications for use with AutoCAD. ObjectARX can be obtained at the Autodesk Web site (www.objectarx.com).

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Summary In this chapter, you learned some basic principles of Visual Basics for Applications as applied to AutoCAD. Specifically, I discussed: n n n n n n n

Working with the VBA development environment Understanding VBA objects, methods, and properties Principles of writing VBA code How to get user input How to create dialog boxes How to modify objects Methods of debugging and trapping errors

A Final Word AutoCAD offers almost unlimited potential for the design and drawing of real-world objects. I hope that this book helps you to understand the world of AutoCAD and makes it easier for you to create the professional drawings that you need to redesign the world and make it a better place. Although I cannot provide technical support for my readers, I would be happy to hear your comments and suggestions at [email protected]. Best wishes and enjoy!

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