The UserControl Object

The UserControl object is the basis for any custom ActiveX control. It provides the container that holds all the rest of the control's features. You may initiate your project's UserControl in one of two ways:

• Begin your project as an ActiveX Control project (see Figure 13.1).

• Add a UserControl object to your existing project (see Figure 13.2).

If you chose to add a UserControl to your project, then the project is probably not an ActiveX project to begin with. This may be exactly the situation you desire if you've chosen to implement your ActiveX control as part of another project (see "ActiveX Controls in Other Projects"). If, however, you wish to convert your project to an ActiveX control project, all you need to do is change the Project Type option on the General tab of the Project Property dialog box (see Figure 13.3).

FIGURE 13.1 Beginning your project as an ActiveX Control project.

FIGURE 13.2 Adding a UserControl object to your project

FIGURE 13.3 Adjusting the project type

Programming with a UserControl is a lot like programming with a form. The UserControl object has its own Designer Window in the VB design-time environment, just like a form does, and a UserControl appears as one of your project's elements in the Project Explorer. It appears under a special node labeled "User Controls." You place constituent controls on the surface of the User Control from the toolbox, just as you do when programming with a form.

The UserControl has its own properties, which we discuss in some of the following sections. You can access these properties at design-time just like you'd access the design-time properties of a form:

Make sure that you've selected the UserControl object itself (and not one of its constituent controls), and then go to the Properties Window by pressing F4 or right-clicking the mouse.

To access a UserControl 's event procedures, make sure that you've selected the UserControl itself (and not one of its constituent controls), then double-click the mouse to view UserControl code.

• Giving Your Control a Custom Bitmap

• Accessing Ready-Made Control Features with the UserControl's Extender Object

• Getting Information About Your Control's Environment with the Ambient Object and the AmbientChanged Event

• Comparison of the Ambient and Extender Objects

NOTE - Referring to the UserControl 's Members in Code : When you write code in the UserControl, you can refer to the UserControl's own built-in members (properties and methods) by referring to the members alone without reference to the UserControl object. For example:

BackColor = vbRed

This is similar to the way that you can program within a Form. Note, however, that the Me keyword does not work in a UserControl (you will receive a compile- time error if you use Me).