The framework calls this member function when the user double-clicks the middle mouse button.
Only windows that have the CS_DBLCLKS WNDCLASS style will receive OnMButtonDblClk calls. This is the default for all Microsoft Foundation Class windows. Windows generates an OnMButtonDblClk call when the user presses, releases, and then presses the middle mouse button again within the system's double-click time limit. Double-clicking the middle mouse button actually generates four events: WM_MBUTTONDOWN and WM_MBUTTONUP messages, the WM_MBUTTONDBLCLK call, and another WM_MBUTTONUP message.
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.