Avoiding use of null
How do you avoid the "Invalid use of null" error when reading null values from a database?If you try to retrieve a null value (empty field) from a database, you will get the error: "Invalid use of Null". Here is one way to get around this problem: ..
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TextBox.Text = MyTest.Fields("TestFld") & ""
. For example, to create CEdit control, you can do the following:
1) add a member variable m_ec_myedit to your dialog .h file;
2) I assume that your dialog templete has some control with ID = IDC_ABOVE_DYNAMIC_EDIT, and you want your dynamically created edit control to have the same width and be placed under IDC_ABOVE_DYNAMIC_EDIT. Then add the following code under the call to CDialog::OnInitDialog() in your overriden OnInitDialog():
GetDlgItem(IDC_ABOVE_DYNAMIC_EDIT)->GetWindowRect(rect);
ScreenToClient(rect);
CRect rectNew(rect.left, rect.bottom+5, rect.right, rect.bottom+35);
m_myEdit.CreateEx(WS_EX_CLIENTEDGE, "EDIT", NULL
/*lpszWindowName*/,
WS_CHILD|WS_VISIBLE|WS_GROUP|WS_TABSTOP|WS_BORDER, rectNew.left, rectNew.top,
rectNew.Width(), rectNew.Height(), this->GetSafeHwnd(), NULL, NULL);
m_myEdit.ShowWindow(SW_SHOW);
It's that simple. The only thing that differs for different control classes is window styles. Usually, you can find the most important of style and extended style constants in online help.
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