Capturing keystrokes in child controls

Question

Hi

I have made a program in C with Visual C++ 2010 Express, and I need to capture keystrokes when child controls have focus. As I have understood, the way to do this is by what is called subclassing. I have tried to implement a solution given by Petzold in his book, chapter 9, but can’t make it work.

First I have changed the message loop in Winmain into the following:

 while( GetMessage(&msg, NULL, 0, 0)) {
    
	if(!IsDialogMessage(hwnd2,&msg)) 
    {                                    
       TranslateMessage(&msg);      
       DispatchMessage(&msg);
    }  
	  

I have read that this is necessary to make it possible to change focus by using the Tab key. Then I have the following callback function:

LRESULT CALLBACK KeyCatching (HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
	
{
if(message==WM_KEYDOWN) tescounter++; 
return CallWindowProc (KeyControl[0], hwnd, message, wParam, lParam) ;
}

I am for now only using a counter to check if I am able to capture any keystrokes at all. The rest I guess I can handle if I only can get it to work. Then I am calling this funtion in the WM_CREATE section in WndProc:

Control[0] = CreateWindow(TEXT("combobox"), NULL, 
                  WS_CHILD | WS_VISIBLE | WS_TABSTOP | CBS_DROPDOWN, 
                  0, 0, 0, 0, hwnd, NULL, g_hinst, NULL);  

		SendMessage(Control[0], CB_ADDSTRING, 0, (LPARAM) comboboxkeynoteitems[0]);
		SendMessage(Control[0], CB_ADDSTRING, 0, (LPARAM) comboboxkeynoteitems[1]);
		SendMessage(Control[0], CB_ADDSTRING, 0, (LPARAM) comboboxkeynoteitems[2]);
		SendMessage(Control[0], CB_ADDSTRING, 0, (LPARAM) comboboxkeynoteitems[3]);
		SendMessage(Control[0], CB_ADDSTRING, 0, (LPARAM) comboboxkeynoteitems[4]);
		SendMessage(Control[0], CB_ADDSTRING, 0, (LPARAM) comboboxkeynoteitems[5]);
		SendMessage(Control[0], CB_ADDSTRING, 0, (LPARAM) comboboxkeynoteitems[6]);
		SendMessage(Control[0], CB_ADDSTRING, 0, (LPARAM) comboboxkeynoteitems[7]);
		SendMessage(Control[0], CB_ADDSTRING, 0, (LPARAM) comboboxkeynoteitems[8]);
		SendMessage(Control[0], CB_ADDSTRING, 0, (LPARAM) comboboxkeynoteitems[9]);
		SendMessage(Control[0], CB_ADDSTRING, 0, (LPARAM) comboboxkeynoteitems[10]);
		SendMessage(Control[0], CB_ADDSTRING, 0, (LPARAM) comboboxkeynoteitems[11]);
		
		SendMessage(Control[0], CB_SETCURSEL, 0, 0); 


KeyControl[0] = (WNDPROC) SetWindowLongPtr (Control[0], GWL_WNDPROC, (LONG) KeyCatching) ;

Finally I have KeyControl as a global variable:

WNDPROC KeyControl[1];

I guess I then would have to make one instance of the call to the KeyCatching function for each of the controls that I want to capture keystrokes from.

However, this doesn' work, and I have come to the end of my reasoning and am stuck. Greatly appreciated if someone could help me with this.

Thanks in advance.

Sincerely

Answer 1

WM_KEYDOWN is reveived by the Edit control  of a CBS_DROPDOWN Combo Box

(the Combo Box receives Edit control notifications such EN_CHANGE in WM_COMMAND)

And if you want to subclass many Combo Boxes, use Superclassing instead (GetClassInfo() + RegisterClass())

Answer 2

Thank you very much. That solved it. Now works.

Sincerely

Answer 3

Since your problem has been resolved, please mark the thread answered.

Answer 4

Actually, there is one more issue related to this. The reason why I wanted to be able to catch keypresses in the child controls is that I want them to bring the focus back to the main window. So that pressing for instance a character key when a child control has the focus, the focus is automatically brought back to the main window. Is there any way to do this?

Thanks in advance.

Sincerely

Answer 5

Actually, there is one more issue related to this. The reason why I wanted to be able to catch keypresses in the child controls is that I want them to bring the focus back to the main window. So that pressing for instance a character key when a child control has the focus, the focus is automatically brought back to the main window. Is there any way to do this?

This is a different question.  It would be appropriate to mark the answer to close this thread and start a new thread for your next question.

Answer 6

Okay. I'll do that.

Sincerely