有关位图的问题

两个图片资源"pic"(ht)"gaga"(Ht)

int WINAPI WinMain(HINSTANCE hInstance,HINSTANCE hPrevInstance,LPSTR lpCmdLine,int nCmdShow)
{MSG msg;
Ht=LoadBitmap(hInstance,"gaga");
GetObject(Ht,sizeof(BITMAP),LPVOID(&bm));

ht=LoadBitmap(hInstance,"pic");
GetObject(ht,sizeof(BITMAP),LPVOID(&bm));}
...
...
case WM_CREATE:
hdc=GetDC(hwndmain);
hdcmem=CreateCompatibleDC(hdc);

ReleaseDC(hwndmain,hdc);
...
...
最后用bitblt输出
SelectObject(hdcmem,ht);
BitBlt(hdc,0,0,bm.bmWidth,bm.bmHeight,hdcmem,0,0,SRCCOPY);

...
...
SelectObject(hdcmem,Ht);
BitBlt(hdc,150,200,bm.bmWidth,bm.bmHeight,hdcmem,0,0,SRCAND);
invalidaterect刷新窗口以后，再用bitblt输出"gaga"，结果显示不出那张图片("gaga")了
这是为什么？和hdcmem有关吗？
诚恳的提问。