1

我需要在 DataGridView 中获取 ComboBox 的选定值。我让它部分工作，但如果我更改网格中的另一个 ComboBox，我会得到一个空引用异常。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，但如果更改另一个 ComboBox，则会生成空引用异常。任何想法为什么会发生这种情况？注意：我在 MSDN 的讨论表单中找到了大部分代码。

谢谢！

彼得

4

3 回答 3

2

最好在不需要时避免使用全局变量。

在尝试访问以下属性之前，您只需要测试是否没有组合框comboBox：

Private Sub ComboBox_SelectedIndexChanged(ByVal sender As Object, ByVal e As EventArgs)
    Dim comboBox As ComboBox = CType(sender, 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，新旧组合框都会调用此 SelectedIndexChanged 事件。我怀疑当它被调用 oldcomboBox时，发件人是 null/Nothing 因为它的值正在改变。也许。但无论发生什么，空值就是空值。在尝试访问它的任何属性之前，只需测试它不为空。

于 2013-10-02T20:39:39.677 回答
1

尝试检查comboBox.SelectedItem.ToString而不是comboBox.SelectedValue.ToString

希望有帮助。

于 2011-06-13T14:55:22.427 回答
0

我有同样的问题。通过对代码进行小的更改进行整理。

声明一个全局变量

Dim comboBoxCol As New DataGridViewComboBoxColumn
Dim gol As Integer = 0



 Dim comboBox As ComboBox
    Private Sub dgvSampleList_EditingControlShowing(ByVal sender As Object, ByVal e As DataGridViewEditingControlShowingEventArgs) Handles DGVItems.EditingControlShowing
        comboBox = CType(e.Control, ComboBox)

        If (comboBox IsNot Nothing) Then

            'Add the event handler.  
            AddHandler comboBox.SelectedIndexChanged, New EventHandler(AddressOf ComboBox_SelectedIndexChanged)
            gol = 1
            'AddHandler comboBox.SelectionChangeCommitted, New EventHandler(AddressOf ComboBox_SelectedIndexChanged)
        End If
    End Sub

    Private Sub ComboBox_SelectedIndexChanged(ByVal sender As Object, ByVal e As EventArgs)
        comboBox = CType(sender, ComboBox)
        If gol = 1 Then
            Dim item As String = comboBox.Text
            MsgBox(item)
            gol = 0
        End If
  End Sub
于 2011-12-14T12:35:17.420 回答