今天在使用DataGrid的下拉列表列時因設定SelectedValueBinding="{Binding 觸發沿, Mode=OneWay}"，導致下拉列表一直無法顯示，查詢半天最後發現將Mode改成TwoWay，問題解決。

<DataGrid VerticalAlignment="Stretch" x:Name="dgItems"
      Height="Auto"
      SelectionUnit="FullRow" SelectionMode="Extended" CanUserAddRows="False"
      DataContext="{Binding}"
 
 Width="Auto" AutoGenerateColumns="False"
      FontSize="16" AlternatingRowBackground="LightBlue"
      AlternationCount="2" Margin="10, 10" Background="Transparent"
      ScrollViewer.VerticalScrollBarVisibility="Visible">
    <DataGrid.Resources>
        <col:ArrayList x:Key="key_triggerList"
 
>
            <col:DictionaryEntry Key="上升沿" Value="上升沿"/>
            <col:DictionaryEntry Key="下降沿" Value="下降沿"/>
        </col:ArrayList>
        <col:ArrayList x:Key="key_attenuatorList">
            <col:DictionaryEntry Key=" 0dB" Value="0"/>
            <col:DictionaryEntry
 
 Key="20dB" Value="20"/>
            <col:DictionaryEntry Key="40dB" Value="40"/>
            <col:DictionaryEntry Key="60dB" Value="60"/>
        </col:ArrayList>
    </DataGrid.Resources>
    <DataGrid.Columns>
        <DataGridTextColumn Header="IP" Width="120*" Binding="{Binding IP, Mode=OneWay}" />
        <DataGridComboBoxColumn Header="觸發沿" Width="80*" IsReadOnly="False" DisplayMemberPath="Key" SelectedValuePath="Value" SelectedValueBinding="{Binding 觸發沿, Mode=TwoWay}"  ItemsSource="{StaticResource key_triggerList}"/>
        <DataGridTextColumn Header="觸發電平(V)" IsReadOnly="False"  Width="80*" Binding="{Binding 觸發電平, Mode=TwoWay}" />
        <DataGridComboBoxColumn Header="衰減器" IsReadOnly="False" Width="80*" DisplayMemberPath="Key" SelectedValuePath="Value" SelectedValueBinding="{Binding 衰減器, Mode=TwoWay}" ItemsSource="{StaticResource key_attenuatorList}"/>
    </DataGrid.Columns>
</DataGrid>

注意在xaml的<window/>節增加

<window xmlns:col="clr-namespace:System.Collections;assembly=mscorlib">

</window>