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Figure 37-4: The help page for the Center Property.

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:

The ActiveX and VBA Reference is an alphabetical listing of objects, methods, properties, and events.

The ActiveX and VBA Developer’s Guide explains ActiveX automation concepts and techniques.

To access these reference guides, switch to AutoCAD and choose Help 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 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 placing the cursor over it and pressing F1. For example, you can type AddLine and press F1 to access help on how to create a line.

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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When you start to create code, VBA can create the basic structure for each procedure for you. Choose Insert Procedure (the Object Browser must be closed) 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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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()

‘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:

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.

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 file name 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.

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.

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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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.

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.

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.

Lines 12–14: Set the length, width, and height of the box to 5.

Line 15: Another comment.

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).

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?

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.

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.

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 2006 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 opened, 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 color-codes your text as you go. The most common colors are:

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

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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.

STEPS: Creating, Saving, and Running a VBA Program

1.Open 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#

‘insert the torus

Set myTorus = ThisDrawing.ModelSpace.AddTorus(dCenter, dRadius1, dRadius2)

‘set the viewpoint and shade it

ThisDrawing.SendCommand (“VPOINT 1,1,1 SHADEMODE GOURAUD “) 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 Macro dialog box, choose DrawTorus and click Run. VBA draws and shades the torus.

Don’t save your drawing.

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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.

Line 6: Declare the variable to hold the radius of the tube.

Line 7: Declare the variable to hold the created 3D object.

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 shade the torus for better viewing.

Line 18: End of subroutine.

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 can 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:

You can specify the type of variable, which usually uses less memory than the default variant type.

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

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You can create three different levels of variables:

A Public variable is available to all procedures in the project. It is shown as follows:

Public dRadius As Double

A module-level variable is available to all of the procedures in the module. You create a module-level 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

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.

Table 37-2 describes the kinds of variables that you can declare.

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Here’s an example that uses the Date variable type and displays it in a message box:

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.

A statement in VBA is the most basic unit of code. It contains a complete instruction. There are three kinds of statements:

A declaration names a variable, constant, or procedure, as in this example:

Dim dOrigin as Double

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

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:

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.

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.

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.