非模态对话框相对于模态对话框，它的创建和销毁过程和模态对话框有一点区别，先看一下MSDN的原文：
When you implement a modeless dialog box, always override the OnCancel member function and call DestroyWindow from within it. Don’t call the base class CDialog::OnCancel, because it calls EndDialog, which will make the dialog box invisible but will not destroy it. You should also override PostNcDestroy for modeless dialog boxes in order to delete this, since modeless dialog boxes are usually allocated with new. Modal dialog boxes are usually constructed on the frame and do not need PostNcDestroy cleanup.
所以：
一、 在非模态对话框中override OnOK和OnCancel
protected:
virtual void OnOK();
virtual void OnCancel();
void CYourDlg::OnOK()
{
this->DestroyWindow();
}
void CYourDlg::OnCancel()
{
this->DestroyWindow();
}
二、 在非模态对话框中override PostNcDestroy
protected:
virtual void PostNcDestroy();
void CYourDlg::PostNcDestroy()
{
CDialog::PostNcDestroy();
delete this;
}
非模态对话框的创建代码一般如下：
CYourDlg *pDlg=new CYourDlg;
pDlg->Create(IDD_DLG_YOUR, this);
pDlg->ShowWindow(SW_SHOW);