通过进程ID获取进程主窗口句柄

typedef struct tagWNDINFO
{
DWORD   dwProcessId;
HWND   hWnd;
}WNDINFO, *LPWNDINFO;

BOOL CALLBACK YourEnumProc(HWND hWnd, LPARAM lParam)
{
DWORD dwProcessId;
GetWindowThreadProcessId(hWnd, &dwProcessId);
LPWNDINFO pInfo = (LPWNDINFO)lParam;
if(dwProcessId == pInfo->dwProcessId)
{
pInfo->hWnd = hWnd;
return FALSE;
}
return TRUE;
}

HWND GetProcessMainWnd(DWORD dwProcessId)
{
WNDINFO wi;
wi.dwProcessId = dwProcessId;
wi.hWnd = NULL;
EnumWindows(YourEnumProc, (LPARAM)&wi);
return wi.hWnd;
}