WM_COMMAND catch button press in c++ win32

Question

I'm trying to get the button press event in c++ win32 using WM_Command

HWND hBtn;
HWND  hBtnParent = HWND("UploadVideo");
HWND SelectVideoBTN, UploadBTN;
HWND hWnd;

HINSTANCE hUpload;
WNDCLASSEX wcexUpload;
int nCmdShowUpload = 1;
using namespace std;

LRESULT CALLBACK WindowProcedure(HWND, UINT, WPARAM, LPARAM);
LRESULT CALLBACK WindowProcedure(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    loader::alert("rrr");
    switch (message)
    {
    case WM_COMMAND:
        if (LOWORD(wParam) == WORD(SelectVideoBTN)) {
            loader::alert("hello");
        }
        break;
    default:
        return DefWindowProc(hwnd, message, wParam, lParam);
    }
    return 0;
}

SelectVideoBTN = CreateWindow(
            L"BUTTON",  // Predefined class; Unicode assumed 
            L"Select Video's",      // Button text 
            WS_TABSTOP | WS_VISIBLE | WS_CHILD | BS_DEFPUSHBUTTON,  // Styles 
            10,         // x position 
            460,         // y position 
            100,        // Button width
            25,        // Button height
            hWnd,     // Parent window
            NULL,       // No menu.
            (HINSTANCE)GetWindowLong(hWnd, GWL_HINSTANCE),
            NULL);      // Pointer not needed.

        UploadBTN = CreateWindow(
            L"BUTTON",  // Predefined class; Unicode assumed 
            L"Upload",      // Button text 
            WS_TABSTOP | WS_VISIBLE | WS_CHILD | BS_DEFPUSHBUTTON,  // Styles 
            390,         // x position 
            460,         // y position 
            100,        // Button width
            25,        // Button height
            hWnd,     // Parent window
            NULL,       // No menu.
            (HINSTANCE)GetWindowLong(hWnd, GWL_HINSTANCE),
            NULL);      // Pointer not needed.

I've been looking at this example - http://forums.devshed.com/programming-42/create-button-clicked-148407.html - but I can't quite get it to work, it won't even call the CALLBACK WindowProcedure - is there anyone who could help me?

The buttons are present on the window I've created, I create the window by doing -

WNDCLASSEX vidUploader;

    vidUploader.cbSize = sizeof(WNDCLASSEX);

    vidUploader.style = CS_HREDRAW | CS_VREDRAW;
    vidUploader.lpfnWndProc = WndProc;
    vidUploader.cbClsExtra = 0;
    vidUploader.cbWndExtra = 0;
    vidUploader.hInstance = hUpload;
    vidUploader.hIcon = LoadIcon(hUpload, MAKEINTRESOURCE(IDI_P2GOVIDEOUPLOADER20));
    vidUploader.hCursor = LoadCursor(NULL, IDC_ARROW);
    vidUploader.hbrBackground = (HBRUSH)(COLOR_WINDOW + 1);
    vidUploader.lpszMenuName = MAKEINTRESOURCE(IDC_P2GOVIDEOUPLOADER20);
    vidUploader.lpszClassName = (LPCWSTR)(L"UploadVideo");
    vidUploader.hIconSm = LoadIcon(wcexUpload.hInstance, MAKEINTRESOURCE(IDI_SMALL));

    RegisterClassEx(&vidUploader);

    hInst = hUpload; // Store instance handle in our global variable

and then to create the window

    hWnd = CreateWindow((LPCWSTR)(L"UploadVideo"), (LPCWSTR)(L"Upload Video's"), WS_OVERLAPPEDWINDOW, CW_USEDEFAULT, CW_USEDEFAULT, 500, 100, NULL, NULL, hUpload, NULL);
if (!hWnd)
        {
            MessageBox(NULL, _T("Call to CreateWindow failed!"), _T("Win32 Guided Tour"), NULL);

            return 1;
        }


    // The parameters to ShowWindow explained:
    // hWnd: the value returned from CreateWindow
    // nCmdShow: the fourth parameter from WinMain
    ShowWindow(hWnd,
        nCmdShowUpload);

    UpdateWindow(hWnd);

Speechless

Answer 1

Child windows (i.e. windows with the WS_CHILD window style) are identified by a unique numeric value, often called control ID or window ID. It is passed to the parent when it receives a WM_COMMAND message, for example. You never assigned a control ID to your button controls, though, and the parent window cannot identify them. In case of a child window, the hMenu parameter in the call to CreateWindow is overloaded to carry the unique identifier:

hMenu
For a child window, hMenu specifies the child-window identifier, an integer value used by a dialog box control to notify its parent about events. The application determines the child-window identifier; it must be unique for all child windows with the same parent window.

In other words, your application picks a numeric value to assign to controls. Since the lower IDs are used by the dialog manager already (e.g. IDOK), it is common practice to start assigning control IDs starting at 100 (see Why do dialog editors start assigning control IDs with 100?).

In your WM_COMMAND handler you can then compare LOWORD(wParam) to the identifier assigned to your button controls.

You need to apply the following changes to your code.

// Declare control IDs. This is usually done in a file called Resource.h
#define IDC_SELECT_VIDEO (100)

Change your window creation code:

SelectVideoBTN = CreateWindow(
            L"BUTTON",  // Predefined class; Unicode assumed 
            L"Select Video's",      // Button text 
            WS_TABSTOP | WS_VISIBLE | WS_CHILD | BS_DEFPUSHBUTTON,  // Styles 
            10,         // x position 
            460,        // y position 
            100,        // Button width
            25,         // Button height
            hWnd,       // Parent window
            (HMENU)IDC_SELECT_VIDEO, // Assign appropriate control ID
            (HINSTANCE)GetWindowLong(hWnd, GWL_HINSTANCE),
            NULL);      // Pointer not needed.

Check for the control ID in your WM_COMMAND handler:

    switch (message)
    {
    case WM_COMMAND:
        if (LOWORD(wParam) == IDC_SELECT_VIDEO) {
            loader::alert("hello");
        }
        break;
    default:
        return DefWindowProc(hwnd, message, wParam, lParam);
    }

---

If your window procedure isn't called at all, this could mean that you aren't dispatching messages on the calling thread. A GUI thread always needs a message loop. The standard message loop suffices:

MSG msg = {0};
while (GetMessage(&msg, NULL, 0, 0))
{
    TranslateMessage(&msg);
    DispatchMessage(&msg);
}

Cootie

I've done what you said, but when I put the .dll file into the program (I'm creating a plugin) the window is generated on load, but when I click on the buttons they don't work, I've edited my question – Speechless

@Gerwin: Please don't change a question in a way, that invalidates a published answer. I reverted your edits to the initial version. If you have a new question, click the Ask Question button. If you want to add more information, you can also edit your question if it doesn't change the core issue. – Cootie

Alright, thank you for the information I just have 1 issue, I can't use a message loop, because it would make the program stuck in the loop & not load the rest of the program, as I'm creating a plugin – Speechless

Then the thing that loads your plugin needs to run a message loop. – Dong

@JonathanPotter there's no alternative method? – Speechless

You can't have a window without a message loop. Something has to run it. You could try using a separate thread I guess but that could get messy. – Dong

@JonathanPotter the developers recommended creating a seperate thread, I'll give that a shot, thank you :) – Speechless

Just FYI, using a Control ID is not the only way to identify a child control. WM_COMMAND and WM_NOTIFY messages that are sent to a parent window carry the child control's HWND as well, eg: case WM_COMMAND: if (HWND(lParam) == SelectVideoBTN) { ... } – Immediate

For a poorly worded question, this is a very good answer! – Pearse

Thanks for the link to the Raymond Chen article, I couldn't find any documentation on MSDN explicitly stating that user-set control IDs couldn't be certain values (and was encountering strange bugs in my own code as a result). – Wilbur

Answer 2

According to Documents of MSDN, the lParam returns handle to the control (window) and the low word (LOWORD) of wParam returns the identifier of the control and high word (HIWORD) of wParam returns notification code in WM_COMMAND message.

Method 1 Without Identifier

If else:

case WM_COMMAND: {

     if((HWND)lParam==SelectVideoBTN) {
        printf("Button was clicked!\n"); //Do whatever you wish
     }

}

Method 2 With Identifier

Step 1: Declare a global Macro with identifier value. The name and ID can be anything you wish but it must be unique throughout the project. Like this...

#define VDOBTN_ID 440 

Then, Step2:

case WM_COMMAND: {

  switch(LOWORD(wParam)){
      case VDOBTN_ID:{
        printf("Button was clicked\n"); // Do whatever you wish
        break;
      }
  }

}

With if else, it should look like this...

case WM_COMMAND: {

  if(LOWORD(wParam)==VDOBTN_ID){
    printf("Button was clicked\n"); // Do whatever you wish
  }

}

If it's not for specific purpose , I personally prefer and recommend the first method as it simplifies the procedure and eliminates the need of another Macro definition and observation of HIWORD and LOWORDs. Comments and corrections are welcome...

Acromegaly