Determine which control a message came from

This is a discussion on Determine which control a message came from within the Windows Programming forums, part of the Platform Specific Boards category; I have a dialog with several checkboxes. The code that is executed when one of the checkboxes is clicked is ...

  1. #1
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    Determine which control a message came from

    I have a dialog with several checkboxes. The code that is executed when one of the checkboxes is clicked is very similar for all checkboxes. I would like to be able to set the ON_BN_CLICKED macro for all my checkboxes to execute the same function then determine from which checkbox the message came.
    Does anyone know of a way to determine what control a message came from?

  2. #2
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    Take a look at the Windows Programming Reference, the part about buttons/notification messages:

    Code:
    When the user selects a button, its state changes, and the button sends notification messages to its parent window. For example, a push button control sends the BN_CLICKED notification message whenever the user chooses the button. In all cases, the low-order word of the wParam parameter contains the control identifier, the high-order word of wParam contains the notification code, and the lParam parameter contains the control window handle.
    Also take a look at how BM_CLICKED message is sent:

    Code:
    The parent window of the button receives this notification message through the WM_COMMAND message.
    So just get the WM_COMMAND message and search for a HIWORD(wParam) that matches BN_CLICKED; there you will have the checkbox id as LOWORD(wParam) and the checkbox handle as lParam

    Hope that helps

  3. #3
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    The LOWORD(wParam) will only be vaild if the child control had the HMENU param set (to an ID number) when it was created (or the control was created using a resource editor that stores a list of ID numbers in resource.h).

    Code:
    case WM_COMMAND:
    
    int CtrlID = LOWORD(wParam);
    
    switch (CtrlID)
    {
         case CB_NUM1:
         case CB_NUM2:
         .....
         case CB_NUMX:
            if(HIWORD(wParam) == BN_CLICKED)
            {
                  return  DoCBProcessing(CtrlID);//handler determines return to OS
            }
         break;
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  4. #4
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    Quote Originally Posted by roakes499 View Post
    I have a dialog with several checkboxes. The code that is executed when one of the checkboxes is clicked is very similar for all checkboxes. I would like to be able to set the ON_BN_CLICKED macro for all my checkboxes to execute the same function then determine from which checkbox the message came.
    Does anyone know of a way to determine what control a message came from?
    Here's a section of the resource file that creates a dialog box...
    Code:
    SETUP0 DIALOGEX DISCARDABLE 8, 18, 299, 178
    STYLE DS_SHELLFONT|WS_CHILD|WS_VISIBLE
    EXSTYLE WS_EX_CONTROLPARENT|WS_EX_TOPMOST
    FONT 8, "Tahoma", 0, 0, 1
    {
      CONTROL "", 4001, "ListBox", LBS_MULTIPLESEL|LBS_SORT|LBS_NOINTEGRALHEIGHT|LBS_NOTIFY|WS_VSCROLL|WS_BORDER|WS_TABSTOP, 22, 19, 256, 44
      CONTROL "Add", 4002, "Button", BS_FLAT|WS_TABSTOP, 22, 65, 50, 14
      CONTROL "Remove", 4003, "Button", BS_FLAT|WS_TABSTOP, 92, 65, 50, 14
      CONTROL "Clear", 4004, "Button", BS_FLAT|WS_TABSTOP, 228, 65, 50, 14
      CONTROL "", 4005, "ListBox", LBS_MULTIPLESEL|LBS_SORT|LBS_NOINTEGRALHEIGHT|LBS_NOTIFY|WS_VSCROLL|WS_BORDER|WS_TABSTOP, 22, 107, 256, 44
      CONTROL "Add", 4006, "Button", BS_FLAT|WS_TABSTOP, 22, 153, 50, 14
      CONTROL "Remove", 4007, "Button", BS_FLAT|WS_TABSTOP, 92, 153, 50, 14
      CONTROL "Clear", 4008, "Button", BS_FLAT|WS_TABSTOP, 228, 153, 50, 14
      CONTROL " VC++  Program paths for X86 ", 4050, "Button", BS_GROUPBOX, 12, 7, 275, 79, WS_EX_TRANSPARENT
      CONTROL " VC++ Program paths for X64 ", 4051, "Button", BS_GROUPBOX, 12, 94, 275, 79
    }
    See all the numbers starting with 4001 ... 4051 ... those are control ID numbers that are passed to message tosser in the lowword of the WM_COMMAND message's WPARAM. So you need to

    Code:
    switch (LOWORD(wParam))
       case ...
    As Novacain has already explained.

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