我需要在DataGridView中获取ComboBox的选定值.我有部分工作,但如果我在网格中更改另一个ComboBox,我会得到一个Null Reference Exception.这是我的代码：
Private Sub dgvSampleList_EditingControlShowing(ByVal sender As Object,ByVal e As DataGridViewEditingControlShowingEventArgs) Handles dgvSampleList.EditingControlShowing
Dim comboBox As ComboBox = CType(e.Control,ComboBox)
If (comboBox IsNot Nothing) Then
'Remove an existing event-handler
RemoveHandler comboBox.SelectedIndexChanged,New EventHandler(AddressOf ComboBox_SelectedIndexChanged)
'Add the event handler.
AddHandler comboBox.SelectedIndexChanged,New EventHandler(AddressOf ComboBox_SelectedIndexChanged)
End If
End Sub
Private Sub ComboBox_SelectedIndexChanged(ByVal sender As Object,ByVal e As EventArgs)
Dim comboBox As ComboBox = CType(sender,ComboBox)
'Display selected value
MsgBox("ProgramID: " & comboBox.SelectedValue.ToString)
End Sub
这在第一次更改ComboBox时工作正常,但如果另一个ComboBox发生更改,则会生成Null Reference Exception.任何想法为什么会这样？注意：我在MSDN的讨论表中找到了大部分此代码.
谢谢！
彼得
当不必要时,最好避免使用全局变量.
在尝试访问comboBox的属性之前,您只需要测试comboBox是否为空：
Private Sub ComboBox_SelectedIndexChanged(ByVal sender As Object,ComboBox) 'Display selected value If comboBox IsNot Nothing Then MsgBox("ProgramID: " & comboBox.SelectedValue.ToString) End If End Sub
在我看来,当comboBox从旧值设置为新值时,将为旧组合框和新组合框调用此SelectedIndexChanged事件.我怀疑当它被旧的comboBox调用时,发送者为null / Nothing,因为它的值正在变化.也许.但无论发生什么,null都是null.在尝试访问其任何属性之前,只测试它不是null.