C++ Why Sendmessage doesnt work?

问题

In C#, this SendMessage function raise up volume successfull:

[DllImport("user32.dll")]
public static extern IntPtr SendMessage(IntPtr hWnd, int Msg, int wParam, int lParam);

SendMessage(Handle, 0x319, (int)Handle, APPCOMMAND_VOLUME_UP);

But in C++, this SendMessage function dont work, that is volume doesnt rise up:

// HWND hwnd = CreateWindow(...
SetWindowText(hwnd, "Hi"); // Worked
SendMessage(hwnd, WM_APPCOMMAND, (int)hwnd, APPCOMMAND_VOLUME_UP); // Don't work

What do I wrong? Can you help me how to fix it? Thank you!

Full code:

#include <windows.h>
HHOOK _hhook;
HWND hwnd;
HINSTANCE _hInstance;

KBDLLHOOKSTRUCT kbdStruct;

LRESULT __stdcall HookCallback(int nCode, WPARAM wParam, LPARAM lParam)
{
    if (nCode >= 0)
    {
        if (wParam == WM_KEYDOWN)
        {
            // lParam is the pointer to the struct containing the data needed, so cast and assign it to kdbStruct.
            kbdStruct = *((KBDLLHOOKSTRUCT*)lParam);
            // a key (non-system) is pressed.
            if (kbdStruct.vkCode == VK_F1)
            {
                // F1 is pressed!
                SetWindowText(hwnd, "Hi");
                SendMessage(hwnd, WM_APPCOMMAND, (WPARAM)hwnd, APPCOMMAND_VOLUME_UP);
                //MessageBox(NULL, "F1 is pressed!", "key pressed", MB_ICONINFORMATION);
            }
        }
    }
    return CallNextHookEx(_hhook, nCode, wParam, lParam);
}

LRESULT CALLBACK WndProc( HWND hwnd, UINT message, WPARAM wparam, LPARAM lparam );
int WINAPI WinMain( HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR szCmdLine, int iCmdShow );

int WINAPI WinMain( HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR szCmdLine, int iCmdShow ) 
{
    WNDCLASS wc;
    wc.cbClsExtra = 0;
    wc.cbWndExtra = 0;
    wc.hbrBackground = (HBRUSH)GetStockObject( WHITE_BRUSH );
    wc.hCursor = LoadCursor( NULL, IDC_HAND );
    wc.hIcon = LoadIcon( NULL, IDI_APPLICATION );
    wc.hInstance = hInstance;
    wc.lpfnWndProc = WndProc;
    wc.lpszClassName = TEXT("Philip");
    wc.lpszMenuName = 0;
    wc.style = CS_HREDRAW | CS_VREDRAW;

    RegisterClass( &wc );
    hwnd = CreateWindow(
        TEXT("Philip"),
        TEXT("Hello World!"),
        WS_OVERLAPPEDWINDOW,
        10, 10,
        500, 200,
        NULL, NULL,
        hInstance, NULL );

    ShowWindow(hwnd, iCmdShow );
    UpdateWindow(hwnd);

    _hhook = SetWindowsHookEx(WH_KEYBOARD_LL, HookCallback, NULL, 0);

    MSG msg;
    while( GetMessage( &msg, NULL, 0, 0 ) )
    {
        TranslateMessage( &msg );
        DispatchMessage( &msg );
    }
    return msg.wParam;
}

LRESULT CALLBACK WndProc(   HWND hwnd,
                            UINT message,
                            WPARAM wparam,
                            LPARAM lparam )
{

    switch( message )
    {

    case WM_DESTROY:
        PostQuitMessage( 0 ) ;
        return 0;
        break;


    }
    return DefWindowProc( hwnd, message, wparam, lparam );
}

回答1:

You need to use MAKELPARAM macro to pass APPCOMMAND_VOLUME_UP to SendMessage MAKELPARAM(0,APPCOMMAND_VOLUME_UP) Final version should look like

SendMessage(hwnd, WM_APPCOMMAND, (WPARAM)hwnd, MAKELPARAM(0,APPCOMMAND_VOLUME_UP));

回答2:

After some investigation I was able to get this working. The problem stems from passing an improperly formed lParam value. The command itself resides in the upper 16 bits of the value but you are not accounting for this. The following change should get you on your way:

SendMessage(hwnd, WM_APPCOMMAND, (WPARAM)hwnd, APPCOMMAND_VOLUME_UP << 16);

来源：https://stackoverflow.com/questions/16110295/c-why-sendmessage-doesnt-work

标签

c++

winapi

handle

sendmessage

hwnd