CreateDialogParamA 的DLGPROC参数类型转换无效怎么解决？

Question

CreateDialogParamA 的DLGPROC参数类型转换无效怎么解决？

CreateDialogParamA(AfxGetInstanceHandle(), MAKEINTRESOURCEA(IDD_DIALOG1), hwnd, (DLGPROC)GoToProc, NULL);

int iLine; // Receives line number.

BOOL fRelative; // Receives check box status.

BOOL CALLBACK CMainWindow::GoToProc(HWND hwndDlg, UINT message, WPARAM wParam, LPARAM lParam)

{

BOOL fError;

switch (message)

{

case WM_INITDIALOG:

    CheckDlgButton((INT)hwndDlg, IDC_BUTTON);

    return TRUE;

case WM_COMMAND:

    switch (LOWORD(wParam))

    {

    case IDOK:

        fRelative = IsDlgButtonChecked((INT)hwndDlg);

        iLine = GetDlgItemInt((INT)hwndDlg,0, fError);

        if (fError)

        {

            MessageBox(L"ok", L"hello", 123);

        

        }

        else

            // Notify the owner window to carry out the task. 

            return TRUE;

    case IDCANCEL:

        DestroyWindow();

        hwndGoto = NULL;

        return TRUE;

    }

}

return FALSE;

}

Answer 1

您好，

在C++中，将类的成员函数作为回调函数传递给另一个函数时，需要注意成员函数的类型和指针的类型之间的差异。因为成员函数有一个隐含的 this 指针参数，无法直接传递成员函数指针作为普通的回调函数。

使用静态成员函数或全局函数

INT_PTR CALLBACK MyDialogClass::s_DlgProc(
    HWND hdlg, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
 MyDialogClass *pThis; // our "this" pointer will go here
 if (uMsg == WM_INITDIALOG) {
  // Recover the "this" pointer which was passed as the last parameter
  // to the ...Dialog...Param function.
  pThis = reinterpret_cast<MyDialogClass*>(lParam);
  // Put the value in a safe place for future use
  SetWindowLongPtr(hdlg, DWLP_USER,
                   reinterpret_cast<LONG_PTR>(pThis));
 } else {
  // Recover the "this" pointer from where our WM_INITDIALOG handler
  // stashed it.
  pThis = reinterpret_cast<MyDialogClass*>(
              GetWindowLongPtr(hdlg, DWLP_USER));
 }
 if (pThis) {
  // Now that we have recovered our "this" pointer, let the
  // member function finish the job.
  return pThis->DlgProc(hwnd, uMsg, wParam, lParam);
 }
 // We don't know what our "this" pointer is, so just do the default
 // thing. Hopefully, we didn't need to customize the behavior yet.
 return FALSE; // returning FALSE means "do the default thing"
}

class MyWindowClass
{
 ... other class stuff goes here ...
 // This is the static callback that we register
 static LRESULT CALLBACK s_WndProc(
    HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam);
 // The static callback recovers the "this" pointer and then
 // calls this member function.
 LRESULT WndProc(
    HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam);
};
void MyWindowClass::SomeMemberFunction()
{
 // to register the class
 WNDCLASS wc;
 ... fill out the window class as normal ...
 wc.lpfnWndProc = MyWindowClass::s_WndProc;
 wc.lpszClassName = TEXT("MyWindowClass");
 RegisterClass(&wc);
 // to create a window
 hwnd = CreateWindow(TEXT("MyWindowClass"),
                     ... other parameters as usual ...,
                     this);
}
class MyDialogClass
{
 ... other class stuff goes here ...
 // This is the static callback that we register
 static INT_PTR CALLBACK s_DlgProc(
    HWND hdlg, UINT uMsg, WPARAM wParam, LPARAM lParam);
 // The static callback recovers the "this" pointer and then
 // calls this member function.
 INT_PTR DlgProc(
    HWND hdlg, UINT uMsg, WPARAM wParam, LPARAM lParam);
};
void MyDialogClass::SomeMemberFunction()
{
 // to create the dialog box
 DialogBoxParam(...  other parameters as usual ...,
                reinterpret_cast<LPARAM>(this));
}

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