KeyBehaviors

KeyBehaviors is a sample that illustrates how to attach behaviors to an MEventTarget so that the behaviors get first chance at the events. In this sample, a subclass of MEventTarget and MKeyEventHandler is defined, TKeyFilterBehavior, that "swallows" certain key events. When this behavior is adopted by another MEventTarget, it prevents those key events from reaching it. In this sample the TKeyInputView class from the previous examples is asked to adopt the behavior.

Running the sample

Execute KeyBehaviorsSApp. With the window active, type some text. Only events that pass the filter (those that match characters in the string 'Taligent') are passed on to the view. Close the window to quit.

Files and classes

TKeyInputView, defined in KeyInputView.h and KeyInputView.C, is much the same as TKeyInputView from KeyEventsInViews. The main difference is that it displays the key text, rather than the key code.

TKeyFilterBehavior, defined in KeyFilterBehavior.h and KeyFilterBehavior.C, derrives from MEventTarget and MKeyEventHandler and overrides KeyDown to filter out events that don't generate characters in the target text 'Taligent'. A true result from KeyDown indicates that the event is handled, effectively "swallowing" it.

KeyBehaviorMain.C simply instantiates the TKeyInputView and TKeyFilterBehavior, and has the view adopt it with MEventHandler::AdoptBehavior.

Notes

By using behaviors, the TKeyInputView class can be unaware of the behavior class, and conversely the behavior class can be unaware of the view.

The list of attached behaviors can be updated dynamically. Behaviors can even themselves have behaviors, so that you can in theory construct complicated behaviors from simpler parts.

Because the event is not const, behaviors can also modify the event passed to them.

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