The framework calls this member function when a nonsystem key is pressed.
A nonsystem key is a keyboard key that is pressed when the ALT key is not pressed or a keyboard key that is pressed when CWnd has the input focus.
Because of auto-repeat, more than one OnKeyDown call may occur before an OnKeyUp member function call is made. The bit that indicates the previous key state can be used to determine whether the OnKeyDown call is the first down transition or a repeated down transition.
For IBM Enhanced 101- and 102-key keyboards, enhanced keys are the right ALT and the right CTRL keys on the main section of the keyboard; the INS, DEL, HOME, END, PAGE UP, PAGE DOWN, and arrow keys in the clusters to the left of the numeric keypad; and the slash (/) and ENTER keys in the numeric keypad. Some other keyboards may support the extended-key bit in nFlags.
This member function is called by the framework to allow your application to handle a Windows message. The parameters passed to your function reflect the parameters received by the framework when the message was received. If you call the base-class implementation of this function, that implementation will use the parameters originally passed with the message and not the parameters you supply to the function.