Question

What is the difference between onKey(), OnKeyDown() and dispatchKeyEvent() methods provided by Android?
I Would like to know when and where each of these can be used.
Please shed some light into this.

Answer 1

Tracing the source code of the 5.1 Source for the View Class. It would seem that dispatchKeyEvent() is the first method called by the system. Overloading it will prevent any and all key events from being called unless the base version is called.

dispatchKeyEvent()‘s first move is to attempt to pass the event to an onKeyListener if there is one. This is when onKey() is called. If the onKey() implementation returns true, dispatchKeyEvent() will return there and other events will not be called.

If there is no onKeyListener or the onKeyListener‘s onKey() method returned false, dispatchKeyEvent() will then call the KeyEvent‘s dispatch() method. Which will then in turn call all the methods in the KeyEvent.Callback interface on your view. This includes onKeyDown() and onKeyUp().