不能打开cfiledialog [英] Cant open cfiledialog

问题描述

我在MFC库的源文件winocc.cpp中的函数GetDlgItem中收到消息未处理的异常抛出：读取访问冲突。这是nullptr

 CWnd * CWnd :: GetDlgItem（int nID）const 
 {
 ASSERT（:: IsWindow（m_hWnd））; 
 
 if（m_pCtrlCont == NULL）
返回CWnd :: FromHandle（:: GetDlgItem（m_hWnd，nID））; 
 else 
返回m_pCtrlCont-> GetDlgItem（nID）; 
} 

此功能来自：

 _AfxActivationWndProc（HWND hWnd，UINT nMsg，WPARAM wParam，LPARAM lParam）
 {
 WNDPROC oldWndProc =（WNDPROC）:: GetProp（hWnd，_afxOldWndProc）; 
 ASSERT（oldWndProc！= NULL）; 
 
 LRESULT lResult = 0; 
 TRY 
 {
 BOOL bCallDefault = TRUE; 
开关（nMsg）
 {
案例WM_INITDIALOG：
 {
 DWORD dwStyle; 
 CRect rectOld; 
 CWnd * pWnd = CWnd :: FromHandle（hWnd）; 
 _AfxPreInitDialog（pWnd，& rectOld，& dwStyle）; 
 bCallDefault = FALSE; 
  lResult =  CallWindowProc （oldWndProc，hWnd，nMsg，wParam，lParam）;  
 _AfxPostInitDialog（pWnd，rectOld，dwStyle）; 
} 
休息; 

我尝试过：



我无法观察 m_pCtrlCont 的值，而this的值为NULL

解决方案

< blockquote>如果 this 的值为NULL，那么当你做错了。



m_pCtrlCont用于CFileDialog的一些高级用法，以增强带有附加窗口的对话框。



我猜你没有实例化CFileDialog对象，但使用了NULL指针。在你创建对话框的地方开始调试。



看一下带有示例的Microsoft文档。

I get the message "Unhandled exception thrown: read access violation. this was nullptr " in function GetDlgItem in source file "winocc.cpp" from MFC library

CWnd* CWnd::GetDlgItem(int nID) const
{
	ASSERT(::IsWindow(m_hWnd));

	if (m_pCtrlCont == NULL)
		return CWnd::FromHandle(::GetDlgItem(m_hWnd, nID));
	else
		return m_pCtrlCont->GetDlgItem(nID);
}

This function is called from :

_AfxActivationWndProc(HWND hWnd, UINT nMsg, WPARAM wParam, LPARAM lParam)
{
	WNDPROC oldWndProc = (WNDPROC)::GetProp(hWnd, _afxOldWndProc);
	ASSERT(oldWndProc != NULL);	

	LRESULT lResult = 0;
	TRY
	{
		BOOL bCallDefault = TRUE;
		switch (nMsg)
		{
		case WM_INITDIALOG:
			{
				DWORD dwStyle;
				CRect rectOld;
				CWnd* pWnd = CWnd::FromHandle(hWnd);
				_AfxPreInitDialog(pWnd, &rectOld, &dwStyle);
				bCallDefault = FALSE;
				lResult = CallWindowProc(oldWndProc, hWnd, nMsg, wParam, lParam);
				_AfxPostInitDialog(pWnd, rectOld, dwStyle);
			}
			break;

What I have tried:

I cant watch the value of m_pCtrlCont and the value of "this" is NULL

解决方案

If the value of this is NULL happens, when you had done something very wrong.

The m_pCtrlCont is used for some advanced use of the CFileDialog to enhance the dialog with a addtional windows.

I guess that you havent instanciated the CFileDialog object, but used pointer which is NULL. Start debugging where you create the dialog.

Take a look at the Microsoft documentation with an example.

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