主题：判断窗口下的所有控件的.Value都不为空

For Each c As object  In e.Form.Controls

    If Typeof c Is WinForm.TextBox OrElse Typeof c Is WinForm.ComboBox OrElse Typeof c Is WinForm.DateTimePicker  Then '判断控件是否是文本框

        If c.Value = Nothing Then

            MessageBox.Show(c.name & "控件不能为空!")

            c.Select()

            Return

        End If

    End If

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