Microsoft

Windows UI Events

Overview

The Windows UI event model provides a set of messages that are sent to window procedures (WndProc) when a user interacts with the graphical interface. These messages are the cornerstone of handling input, system notifications, and control-specific actions in native Win32 applications.

Common Events

MessageDescriptionMacro
WM_CREATESent when a window is being created.WM_CREATE
WM_DESTROYSent when a window is being destroyed.WM_DESTROY
WM_PAINTRequest to repaint the client area.WM_PAINT
WM_CLOSESent when a window is about to close.WM_CLOSE
WM_QUITPosted to exit the message loop.WM_QUIT

Keyboard Events

MessageDescription
WM_KEYDOWNKey pressed (repeatable).
WM_KEYUPKey released.
WM_CHARCharacter generated by a key press.
WM_SYSKEYDOWNSystem key pressed (e.g., ALT).
WM_SYSKEYUPSystem key released.

Mouse Events

MessageDescription
WM_LBUTTONDOWNLeft mouse button pressed.
WM_LBUTTONUPLeft mouse button released.
WM_RBUTTONDOWNRight mouse button pressed.
WM_RBUTTONUPRight mouse button released.
WM_MOUSEMOVEMouse cursor moved.
WM_MOUSEWHEELMouse wheel rotated.

Usage Example

The following minimal Win32 program demonstrates handling of basic UI events such as creation, painting, keyboard input, and mouse clicks.


// SimpleWinEvents.cpp
#include <windows.h>

LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
    switch (msg)
    {
        case WM_CREATE:
            SetWindowText(hwnd, L"UI Events Demo");
            return 0;

        case WM_PAINT:
        {
            PAINTSTRUCT ps;
            HDC hdc = BeginPaint(hwnd, &ps);
            TextOutW(hdc, 10, 10, L"Press any key or click the mouse.", 30);
            EndPaint(hwnd, &ps);
        }
        return 0;

        case WM_KEYDOWN:
            MessageBoxW(hwnd, L"Key pressed!", L"Keyboard", MB_OK);
            return 0;

        case WM_LBUTTONDOWN:
            MessageBoxW(hwnd, L"Left mouse button clicked!", L"Mouse", MB_OK);
            return 0;

        case WM_DESTROY:
            PostQuitMessage(0);
            return 0;
    }
    return DefWindowProcW(hwnd, msg, wParam, lParam);
}

int WINAPI wWinMain(HINSTANCE hInst, HINSTANCE, PWSTR, int nCmdShow)
{
    const wchar_t CLASS_NAME[] = L"DemoWindowClass";

    WNDCLASSW wc = { };
    wc.lpfnWndProc   = WndProc;
    wc.hInstance     = hInst;
    wc.lpszClassName = CLASS_NAME;
    wc.hCursor       = LoadCursor(nullptr, IDC_ARROW);
    RegisterClassW(&wc);

    HWND hwnd = CreateWindowExW(
        0, CLASS_NAME, L"UI Events Demo",
        WS_OVERLAPPEDWINDOW,
        CW_USEDEFAULT, CW_USEDEFAULT, 500, 300,
        nullptr, nullptr, hInst, nullptr);

    if (hwnd == nullptr) return 0;

    ShowWindow(hwnd, nCmdShow);
    UpdateWindow(hwnd);

    MSG msg;
    while (GetMessageW(&msg, nullptr, 0, 0))
    {
        TranslateMessage(&msg);
        DispatchMessageW(&msg);
    }
    return (int)msg.wParam;
}

Compile with:

cl /EHsc SimpleWinEvents.cpp user32.lib gdi32.lib