Visual Basic 6 Black Book:Creating ActiveX Controls And Documents
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There are a few reasons why you may want to create your ActiveX document as an in-process component (DLL file). The performance of an in-process component surpasses that of the same component compiled as an EXE. In addition, multiple programs accessing the same EXE can overwrite global data; that doesn’t happen if they each have their own in-process server.

Which ActiveX Component Do I Want To Build?
With all the different types of ActiveX components to choose from, how do you decide which type of component you want to create? Take a look at this list:


•  To build an invisible component that provides routines in code that you can call, build a code component (ActiveX EXE or an ActiveX DLL).
•  To build a component that can run in the same process with your application, build an ActiveX DLL.
•  To build a component that can serve multiple applications and can run on a remote computer, build an ActiveX EXE.
•  To build a visible component that can be dropped into an application at design time, build an ActiveX control.
•  To build a visible component that can take over an application window at runtime, build an ActiveX document.

That’s it for the overview of ActiveX controls and documents for the moment—it’s time to turn to the Immediate Solutions.

Immediate Solutions
Creating An ActiveX Control
The Testing Department is calling again. Wouldn’t it be great if you built a new ActiveX control that displayed a digital clock? That control could be reused in many other programs. Hmm, you think, how do you create an ActiveX control?

Select the New Project menu item in the Visual Basic File menu to open the New Project dialog box, as shown in Figure 20.1.

Figure 20.1  The New Project dialog box.
Select the ActiveX Control item in the New Project dialog box and click on OK. This creates a new, empty ActiveX control, as shown in Figure 20.2.


Figure 20.2  A new ActiveX control.
Believe it or not, you’ve created your first ActiveX control, UserControl1. You can even run the control with the Run menu’s Start item, which would display the control by launching the Microsoft Internet Explorer if you have it installed in your computer; however, there would be nothing to see because the control is empty.
The default name of the control is Project1, but we can change that to, say, FirstControl. To do that, select the Project1 Properties item in the Project menu, and type “FirstControl” into the Project Name box in the Project Properties dialog box, then click on OK. Also, save the project as firstcontrol.vbp. Instead of a FRM file, you save ActiveX controls in CTL files. Select the Save UserControl1 item in the file menu to save the control as firstcontrol.ctl. Here’s what appears in that file on disk:


VERSION 6.00
Begin VB.UserControl UserControl1
ClientHeight = 3600
ClientLeft = 0
ClientTop = 0
ClientWidth = 4800
ScaleHeight = 3600
ScaleWidth = 4800
End
Attribute VB_Name = "UserControl1"
Attribute VB_GlobalNameSpace = False
Attribute VB_Creatable = True
Attribute VB_PredeclaredId = False
Attribute VB_Exposed = True


Now that we’ve seen how to create a new ActiveX control, it’s time to make it do something. We’ll see how that works in the next topic.

Designing An ActiveX Control From Scratch
The testing department is on the phone. Your new ActiveX control looks fine, but why doesn’t it do anything? Should it? you ask. Yes, they say.

You can design the appearance of your ActiveX control entirely from scratch, creating an entirely new control, never seen before. In that case, you’re responsible for creating the control’s appearance from scratch. Later, you can add events to your control, as well as methods and properties, as we’ll see later in this chapter.
To design the appearance of your entirely new control, you can use the Visual Basic graphics methods that the UserControl object supports, such as Circle, Line, PSet, Print, Cls, and Point. You can also display an image in the UserControl object by setting its Picture property.
Let’s see an example. Here, we’ll just draw two lines to crisscross an ActiveX control and draw a black box in the middle. Create a new ActiveX control now, and double-click it at design time to open the code window to the UserControl_Initialize function:


Private Sub UserControl_Initialize()

End Sub


This function is just like the Form Load procedure that we’re familiar with. Set the control’s AutoRedraw property to True so we can draw graphics from UserControl_Initialize, and then draw the lines to crisscross the control, using the Line method and ScaleWidth and ScaleHeight just as you would in a Visual Basic form:


Private Sub UserControl_Initialize()
Line (0, 0)-(ScaleWidth, ScaleHeight)
Line (0, ScaleHeight)-(ScaleWidth, 0)
...
End Sub


Next, we draw a filled-in black box in the center of the control this way:



Private Sub UserControl_Initialize()
Line (0, 0)-(ScaleWidth, ScaleHeight)
Line (0, ScaleHeight)-(ScaleWidth, 0)
Line (ScaleWidth / 4, ScaleHeight / 4)-(3 * ScaleWidth / 4, _
3 * ScaleHeight / 4), , BF
End Sub


Let’s test this new ActiveX control now in the Microsoft Internet Explorer (assuming you have that browser installed). To do that, just select the Run menu’s Start item now. Doing so opens the Project Properties dialog box, shown in Figure 20.3.


Figure 20.3  The Project Properties window.
Leave UserControl1 in the Start Component box, and make sure the Use Existing Browser box is clicked, then click on OK. This registers our control with Windows, creates a temporary HTML page with the control embedded in it, and starts the Internet Explorer, as you see in Figure 20.4.


Figure 20.4  Our first ActiveX control.
You can see our new ActiveX control in Figure 20.4. Now we’ve created our first ActiveX control and designed its appearance from scratch. If we wanted to, we could add events, properties, and methods to this control (we’ll see how to do so later in this chapter).

Here’s the temporary HTML page that Visual Basic creates to display our ActiveX control; note that our control is registered with Windows and has its own ID, so this page can use the HTML <OBJECT> tag to embed one of our controls in the page:


<HTML>
<BODY>
<OBJECT classid="clsid:B2A69D3B-D38C-11D1-8881-E45E08C10000">
</OBJECT>
</BODY>
</HTML>






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