一个简单CMemDC的错误（高手请进，也许一看即知问题所在）

Question

class CMemDC
{
public:
CMemDC()
{
hMemDC = CreateCompatibleDC(NULL);
hBitmap = CreateCompatibleBitmap(hMemDC, 16, 16);
hOldBitmap = (HBITMAP)SelectObject(hMemDC, hBitmap); SetTextColor(hMemDC, RGB(255,0,0));
TextOut(hMemDC, 0, 0, _T("OK"), 2);
}
virtual ~CMemDC()
{
SelectObject(hMemDC, hOldBitmap);
DeleteObject(hBitmap);
DeleteDC(hMemDC);
}public:
HDC hMemDC;
HBITMAP hBitmap;protected:
HBITMAP hOldBitmap;
};class CMyDlg
{
CMemDC memDC;
};BOOL CMyDlg::OnInitDialog()
{
CStatic *pImage=(CStatic*)GetDlgItem(IDC_IMAGE);
pImage->SetBitmap(memDC.hBitmap);
}
问题是：pImage->SetBitmap(memDC.hBitmap);为什么不起效？
而且，我把CMemDC中所有代码都移入CMyDlg::OnInitDialog()，却又能看到效果。

Answer 1

class CMemDC
{
public:
    CMemDC()
    {
        hMemDC = CreateCompatibleDC(NULL);
        hBitmap = CreateCompatibleBitmap(hMemDC, 16, 16);
        hOldBitmap = (HBITMAP)SelectObject(hMemDC, hBitmap);        SetTextColor(hMemDC, RGB(255,0,0));
        TextOut(hMemDC, 0, 0, _T("OK"), 2);
        SelectObject(hMemDC, hOldBitmap);
    }
    virtual ~CMemDC()
    {
        
        DeleteObject(hBitmap);
        DeleteDC(hMemDC);
    }public:
    HDC hMemDC;
    HBITMAP hBitmap;protected:
    HBITMAP hOldBitmap;
};试试