c - 如何更新窗口内的文本？

Question

我正在尝试创建我的第一个 GUI 应用程序。我只想显示一个文本(可能是一个数字)，然后循环更改/更新它。我找到了一些创建和显示窗口的基本示例，其中包含一些文本，但如何更新文本？有人可以给我看一个简单的例子吗？一个很好的例子是显示时间。

提前致谢!

更新:这是我的代码。这没什么特别的，我只是从 MSDN 上拿了一个例子。

#include <windows.h>  
#include <stdlib.h>
#include <string.h>
#include <tchar.h>

static TCHAR szWindowClass[] = _T( "win32app" );
static TCHAR szTitle[] = _T( "Win32 Guided Tour Application" );

HINSTANCE hInst;

LRESULT CALLBACK WndProc( HWND, UINT, WPARAM, LPARAM );

int WINAPI WinMain( HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow )
{
WNDCLASSEX wcex;

wcex.cbSize = sizeof( WNDCLASSEX );
wcex.style = CS_HREDRAW | CS_VREDRAW;
wcex.lpfnWndProc = WndProc;
wcex.cbClsExtra = 0;
wcex.cbWndExtra = 0;
wcex.hInstance = hInstance;
wcex.hIcon = LoadIcon( hInstance, MAKEINTRESOURCE( IDI_APPLICATION ) );
wcex.hCursor = LoadCursor( NULL, IDC_ARROW );
wcex.hbrBackground = ( HBRUSH )( COLOR_WINDOW + 1 );
wcex.lpszMenuName = NULL;
wcex.lpszClassName = szWindowClass;
wcex.hIconSm = LoadIcon( wcex.hInstance, MAKEINTRESOURCE( IDI_APPLICATION ) );

if ( !RegisterClassEx( &wcex ) )
{
    MessageBox( NULL, _T( "Call to RegisterClassEx failed!" ), _T( "Win32 Guided Tour" ), NULL );

    return 1;
}

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

HWND hWnd = CreateWindow( szWindowClass, szTitle, WS_OVERLAPPEDWINDOW, CW_USEDEFAULT, CW_USEDEFAULT, 500, 100, NULL, NULL, hInstance, NULL );

if ( !hWnd )
{
    MessageBox( NULL, _T( "Call to CreateWindow failed!" ), _T( "Win32 Guided Tour" ), NULL );

    return 1;
}

ShowWindow( hWnd, nCmdShow );
UpdateWindow( hWnd );

HDC hdc;
PAINTSTRUCT ps;
// Main message loop:
MSG msg;
char test[ 100 ] = { 0 };
int i = 0;
while ( GetMessage( &msg, NULL, 0, 0 ) )
{
    i++;
    hdc = BeginPaint( hWnd, &ps );
    sprintf(test, "%d", i);
    TextOutA( hdc, 5, 5, test, strlen( test ) );

    EndPaint( hWnd, &ps );
    TranslateMessage( &msg );
    DispatchMessage( &msg );
}

return ( int )msg.wParam;
}

LRESULT CALLBACK WndProc( HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam )
 {
PAINTSTRUCT ps;
HDC hdc;
TCHAR greeting[] = _T( "Hello, World!" );

switch ( message )
{
    case WM_PAINT:
        hdc = BeginPaint( hWnd, &ps );

        TextOut( hdc, 5, 5, greeting, _tcslen( greeting ) );

        EndPaint( hWnd, &ps );
        break;
    case WM_DESTROY:
        PostQuitMessage( 0 );
        break;
    default:
        return DefWindowProc( hWnd, message, wParam, lParam );
        break;
}

return 0;
}

Answer 1

1) Do not do the drawing in your loop.
2) Only draw in WM_PAINT
3) Create a variable that contains what you want to draw
4) If you want to redraw your window, call InvalidateRect(hWnd, NULL, NULL) and it will post a WM_PAINT message to your window proc.
5) I'd suggest creating a timer that redraws maybe once every 5 seconds. Ideally, you would redraw when something changes the state of your data.  If you redraw every time through your message loop, it's going to continuously redraw and be very unresponsive.