窗口WM_PAINT 消息,始终不触发. 为什么?

[fkestrel]

创建窗口后, WM_PAINT消息始终不触发, 创建窗口后,UpdateWindow(hWnd)也未触发WM_PAINT消息. 请问这是为什么?
整体源码如下:

#include <windows.h>

void Show (HWND hwnd, HDC hdc, int xText, int yText, int iMapMode, TCHAR *szMapMode)
{
	TCHAR szBuffer[60];
	RECT  rect;

	SaveDC(hdc);
	SetMapMode(hdc, iMapMode);
	GetClientRect(hwnd, &rect);
	DPtoLP(hdc, (PPOINT)&rect, 2);

	RestoreDC(hdc, -1);
	TextOut(hdc, xText, yText, szBuffer,
		wsprintf(szBuffer, TEXT("%-20s %7d %7d %7d %7d"), szMapMode,
		rect.left, rect.right, rect.top, rect.bottom));
}

LRESULT CALLBACK WndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
	static TCHAR szHeading[] = TEXT("Mapping Mode Left Right Top Bottom");
	static TCHAR szUndLine[] = TEXT("------------ ---- ----- --- ------");
	static int cxChar, cyChar;
	HDC			hdc;
	PAINTSTRUCT	ps;
	TEXTMETRIC	tm;
	TCHAR		szBuf[64];

	switch (message)
	{
	case WM_CREATE:
		hdc = GetDC(hwnd);
		if (hdc == NULL)
			MessageBox(NULL, TEXT("GetDc Fail!"), TEXT("Err"), MB_OK);
		SelectObject(hdc, GetStockObject(SYSTEM_FIXED_FONT));

		GetTextMetrics(hdc, &tm);
		cxChar = tm.tmAveCharWidth;
		cyChar = tm.tmHeight + tm.tmExternalLeading;

		ReleaseDC(hwnd, hdc);
		return 0;

	case WM_PRINT:
		hdc = BeginPaint(hwnd, &ps);
		SelectObject(hdc, GetStockObject(SYSTEM_FIXED_FONT));
		SetMapMode(hdc, MM_ANISOTROPIC);
		SetWindowExtEx(hdc, 1, 1, NULL);
		SetViewportExtEx(hdc, cxChar, cyChar, NULL); 

		TextOut(hdc, 1, 1, szHeading, lstrlen(szHeading));
		TextOut(hdc, 1, 2, szUndLine, lstrlen(szUndLine));

		Show(hwnd, hdc, 1, 3, MM_TEXT, TEXT("TEXT(pixels)"));
		Show(hwnd, hdc, 1, 4, MM_LOMETRIC, TEXT("LOMETRIC(.lmn)"));
		Show(hwnd, hdc, 1, 5, MM_HIMETRIC, TEXT("HIMETRIC(.01mm)"));
		Show(hwnd, hdc, 1, 6, MM_LOENGLISH, TEXT("LOENGLISH(.01 in)"));
		Show(hwnd, hdc, 1, 7, MM_HIENGLISH, TEXT("HIENGLISH(.001 in)"));
		Show(hwnd, hdc, 1, 8, MM_TWIPS, TEXT("TWIPS(1/1400 in)"));

		EndPaint(hwnd, &ps);
		return 0;

	case WM_SIZE:
		wsprintf(szBuf, TEXT("x:%d y:%d"), LOWORD(lParam), HIWORD(lParam));
			//MessageBox(NULL, szBuf, TEXT("Size"), MB_OK);
		break;

	case WM_DESTROY:
		PostQuitMessage(0);
		return 0;
	}
	return DefWindowProc(hwnd, message, wParam, lParam);
}

int WINAPI WinMain(__in HINSTANCE hInstance, __in_opt HINSTANCE hPrevInstance, __in_opt LPSTR lpCmdLine, __in int nShowCmd )
{
	static TCHAR szWinTitle[] = TEXT("WinMain");
	HWND		hWnd;
	MSG			msg;
	WNDCLASS	wndClass;

	wndClass.style				= CS_HREDRAW | CS_VREDRAW;
	wndClass.lpszClassName		= szWinTitle;
	wndClass.lpfnWndProc		= WndProc;
	wndClass.cbClsExtra			= 0;
	wndClass.cbWndExtra			= 0;
	wndClass.hInstance			= hInstance;
	wndClass.hIcon				= LoadIcon(NULL, MAKEINTRESOURCE(IDI_ICON2));
	wndClass.hCursor			= LoadCursor(NULL, IDC_ARROW);
	wndClass.hbrBackground		= (HBRUSH)GetStockObject(WHITE_BRUSH);
	//wndClass.hbrBackground		= (HBRUSH)(COLOR_BTNFACE + 1);
	wndClass.lpszMenuName		= NULL;

	if (!RegisterClass(&wndClass))
	{
		MessageBox(NULL, TEXT("RegisterClass Fail!!"), TEXT("Err"), MB_OK);
		return 0;
	}

	hWnd = CreateWindow(szWinTitle, TEXT("WinMain"),
						WS_OVERLAPPEDWINDOW,
						CW_USEDEFAULT, CW_USEDEFAULT,
						CW_USEDEFAULT, CW_USEDEFAULT,
						NULL, NULL, hInstance, NULL);
	ShowWindow(hWnd, nShowCmd);
	UpdateWindow(hWnd);

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

	return msg.wParam;
}

[赵4老师]

请检查每个函数调用的返回值。

[酱油党]

//case WM_PRINT:
// as you code , please case WM_PAINT not WM_PRINT
写差了，不是WM_PRINT
而是WM_PAINT 

[飞天御剑流]

主要问题如二楼所说拼写错误，此外补充一下，UpdateWindow并不是一定发送WM_PAINT的，存在无效区域才会发送WM_PAINT消息。

[fkestrel]

[Quote=引用 2 楼 的回复:]

C/C++ code
//case WM_PRINT:
// as you code , please case WM_PAINT not WM_PRINT
写差了，不是WM_PRINT
而是WM_PAINT
[/Quote]

晕. 不细心呐,不细心!! 谢谢!!