组合框的选定值不适用于 DirectCast 或 CType

Question

我试图清除表单上对组合框的选择，但是当将 .SelectedValue 属性设置为 -1 时，我得到的是第一个值。

为了解释headerControls 和controlsList，我在运行时从配置文件创建所有控件，加载到controlsList，当我将控件添加到屏幕时，我还将它添加到headerControls

Public headerControls As New Dictionary(Of String, Control)

Try
    For each dynamicControl As KeyValuePair(Of Integer, CustomControl) In controlsList 
        Select dynamicControl.Value.ControlType.ToLower()
            Case "textbox"
                DirectCast(headerControls.Item(dynamicControl.Value.ControlName), TextBox).Text = ""
            Case "combobox"
                DirectCast(headerControls.Item(dynamicControl.Value.ControlName), ComboBox).SelectedValue = -1
        End Select
    Next
Catch ex As Exception
        'Error Handling
End Try

创建控件的代码：

Try
    For each dynamicControl As KeyValuePair(Of Integer, CustomControl) In controlsList 

        Select Case dynamicControl.Value.ControlType.ToLower()
            Case "textbox"
                Dim textBoxControl As New TextBox

                With textBoxControl
                    'Set Textbox properties here
                End With

                headerControls.Add(dynamicControl.Value.ControlName, textBoxControl)
                Controls.Add(textBoxControl)

            Case "combobox"
                Dim comboBoxControl As New ComboBox

                With comboBoxControl
                    'Set ComboBox properties here
                End With

                LoadCombo(comboBoxControl)

                headerControls.Add(dynamicControl.Value.ControlName, comboBoxControl)
                Controls.Add(comboBoxControl)

        End Select
    Next

Catch ex As Exception
    'Error Handling
End Try

清除文本框有效，但 ComboBox 显示的行为与我将文本框放在屏幕上并使用 .SelectedValue = -1

的行为不同

Answer 1

也许您应该检查SelectedValue 和SelectedIndex 之间的区别。将SelectedValue 设置为一个值不可能选择任何项目。如果您不想选择任何项目，则将SelectedIndex 设置为-1，将SelectedItem 设置为Nothing，或者，根据您的绑定，将SelectedValue 设置为Nothing。