VB.NET-Datagridview组合框过滤器和空值

Question

我已经阅读了DataGridView Cascading/Dependent ComboBox Columns的帖子，并使用datagridview和2列组合框进行了相同的项目，其中第二个组合框通过选择第一个组合框进行了过滤。 我很想有可能在第二个组合框中取消选择，如果用户选择错误，第二个组合框可以清除选择...

这里有我使用的代码： 1）第一个组合框为FASE 2）第二个组合框是SOTTOFASE

Private Sub DataGridView1_EditingControlShowing(sender As Object, e As DataGridViewEditingControlShowingEventArgs) Handles DataGridView1.EditingControlShowing
        Dim grid = DirectCast(sender, DataGridView)
        If (grid.CurrentCell.ColumnIndex = 1) Then 'State column
            Dim combo = DirectCast(e.Control, DataGridViewComboBoxEditingControl)
            If (grid.CurrentRow.Cells(0).Value IsNot DBNull.Value) Then

                Dim dvStates = New DataView(MondoDBDataSet1.Tables("SOTTOFASI"), $"n_fase = '{grid.CurrentRow.Cells(0).Value}'", "n_fase ASC", DataViewRowState.CurrentRows)
                combo.DataSource = dvStates
                combo.ValueMember = "n_sottofase"
                combo.DisplayMember = "sottofase"

            Else
                combo.DataSource = Nothing
            End If
        End If
    End Sub

感谢帮助！

这是3个步骤的图像：

Datagridview steps

解决方案： 我已实现事件KeyUp，并在按下按钮“ del”时将单元格值设置为“ dbnull”

Private Sub DataGridView1_KeyUp(sender As Object, e As KeyEventArgs) Handles DataGridView1.KeyUp
    If GetAsyncKeyState(Keys.Delete) Then

        Dim CellCombo As DataGridViewComboBoxCell

        If DataGridView1.Rows(DataGridView1.CurrentRow.Index).Cells(1).Value <> -1 Then
            CellCombo = DataGridView1.Rows(DataGridView1.CurrentRow.Index).Cells(1)
            CellCombo.Value = DBNull.Value

        End If

    End If
End Sub