Inheriting from Forms and User Controls

Visual Studio .NET allows you to add an inherited form or control as a new item to a project. When you add such an item, it will display the Inheritance Picker dialog, which lists appropriate classes from the solutions in your project (this includes all the forms you have defined, or all the user controls, if you are creating an inherited control). Inheriting from a form or a user control requires the relevant projects in your solution to have been built. If classes you expect to see are missing from the list, check that your solution builds without errors. The Inheritance Picker also provides a Browse button, so that you can derive from classes defined in components outside your solution.

Once you have selected your base class, the usual Forms Designer will be shown, just as it would be for a normal form or composite control. But rather than displaying a blank canvas, the editor will show the contents of the base class—your new user interface element will initially look exactly like its base class. Not surprising, as inherited classes always have all their base class’s members.

Of course, inheritance allows us to extend the functionality of the base class, not just to replicate it, so the editor lets us add new controls to the derived class. The editor annotates base class controls with a small icon, as shown on the text box and button in Figure 6-1, to enable you to tell the difference between controls from the base class and controls ...

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