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GUI for .NET Primer
Controls in Forms : Control sources : ABL-derived controls

ABL-derived controls

An ABL-derived control extends an existing .NET control by customization. ABL-derived controls can be created in the Visual Designer and added to the Visual Designer Toolbox through PROPATH. ABL-derived controls can be added to a form just like any other .NET control.
An example of an ABL-derived control can be something as simple as an OK button. The OK button can be created as a class that inherits from the System.Windows.Forms.Button class. You can then set properties to change the button's shape, color, font, and so on. The button subscribes to the Click event which is then assigned to an event handler method. When dropped onto a .NET form, you can set the form's AcceptButton property to the OK button object reference.
If you are familiar with the object-oriented extensions to ABL, working with .NET objects looks very familiar since the syntax is the same. All .NET objects are referenced by specifying the namespace followed by the .NET object name.