问题描述

为什么我的程序一开始窗口空白，需要改变大小或者最小化，谁能解释这个和一般的程序的不同

#include
#include

#define NUM 1000
#define TWOPI (2 * 3.14159)

LRESULT CALLBACK WndProc(HWND UINT WPARAM LPARAM);

int WINAPI WinMain(HINSTANCE hInstance HINSTANCE hPrevInstance
PSTR szCmdLine int iCmdShow)
{
static TCHAR szAppName[] = TEXT(""SineWave"");
HWND hwnd;
MSG msg;
WNDCLASS wndclass;

wndclass.style = CS_HREDRAW | CS_VREDRAW;wndclass.lpfnWndProc = WndProc;wndclass.cbClsExtra = 0;wndclass.cbWndExtra = 0;wndclass.hInstance = hInstance;wndclass.hIcon = LoadIcon(NULL IDI_APPLICATION);wndclass.hCursor = LoadCursor(NULL IDC_ARROW);wndclass.hbrBackground = (HBRUSH)GetStockObject(WHITE_BRUSH);wndclass.lpszMenuName = NULL;wndclass.lpszClassName = szAppName;if (!RegisterClass(&wndclass)){    MessageBox(NULL TEXT(""Program requires Windows NT!"")        szAppName MB_ICONERROR);    return 0;}hwnd = CreateWindow(szAppName TEXT(""Sine Wave Using Polyline"")    WS_OVERLAPPEDWINDOW    CW_USEDEFAULT CW_USEDEFAULT    CW_USEDEFAULT CW_USEDEFAULT    NULL NULL hInstance NULL);ShowWindow(hwnd iCmdShow);UpdateWindow(hwnd);while (GetMessage(&msg NULL 0 0)){    TranslateMessage(&msg);    DispatchMessage(&msg);}return msg.wParam;

}

LRESULT CALLBACK WndProc(HWND hwnd UINT message WPARAM wParam LPARAM lParam)
{
static int cxClient cyClient;
HDC hdc;
int i;
PAINTSTRUCT ps;
POINT apt[NUM];

switch (message){case WM_SIZE:    cxClient = LOWORD(lParam);    cyClient = HIWORD(lParam);    return 0;case WM_PAINT:    hdc = BeginPaint(hwnd &ps);    MoveToEx(hdc 0 cyClient / 2 NULL);    LineTo(hdc cxClient cyClient / 2);    for (i = 0; i < NUM; i++)    {        apt[i].x = i * cxClient / NUM;        apt[i].y = (int)(cyClient / 2 * (1 - sin(TWOPI * i / NUM)));    }    Polyline(hdc apt NUM);    return 0;case WM_DESTROY:    PostQuitMessage(0);    return 0;}return DefWindowProc(hwnd message wParam lParam);

}

解决方案

调用InvalidateRect强制刷新下客户区