wpf组合框默认值

Question

当 SelectedValue 为 Null 时，我正在尝试将组合框选定项默认设置为索引 = 0。数据触发器有什么问题？错误：无法识别 SelectedIndex 属性

 <ComboBox x:Name="ACombobox" ItemsSource="{Binding Mode=OneWay, Source={StaticResource AList}}" 
                    DisplayMemberPath="TypeName" SelectedValuePath="TypeName" 
                    SelectedValue="{Binding  AnObj.Type, Mode=TwoWay}"  >
                        <ComboBox.Triggers>
                            <DataTrigger Binding="{Binding}" Value="{x:Null}">
                                <Setter Property="SelectedIndex" Value="0" />
                            </DataTrigger>
                        </ComboBox.Triggers>
                    </ComboBox>

Answer 1

您应该通过创建如下样式触发器来完成

<ComboBox x:Name="ACombobox" ItemsSource="{Binding Mode=OneWay, Source={StaticResource AList}}" 
                DisplayMemberPath="TypeName" SelectedValuePath="TypeName" 
                SelectedValue="{Binding  AnObj.Type, Mode=TwoWay}"  >
    <Style TargetType="ComboBox">
        <Style.Triggers>
            <DataTrigger Binding="{Binding}" Value="{x:Null}">
                <Setter Property="SelectedIndex" Value="0" />
            </DataTrigger>
        </Style.Triggers>
    </Style>
</ComboBox>

错误说 it does not have a qualifying type name 因此，当您设置 TargetType="ComboBox"

时，通过创建一个应用于组合框的样式

<ComboBox x:Name="ACombobox" ItemsSource="{Binding AList}"
            DisplayMemberPath="TypeName" SelectedValuePath="TypeName" 
            SelectedValue="{Binding  AnObj.Type, Mode=TwoWay}"   >
  <ComboBox.Resources>
    <Style TargetType="ComboBox">
        <Style.Triggers>
            <DataTrigger Binding="{Binding SelectedItem}" Value="{x:Null}">
                <Setter Property="SelectedIndex" Value="0" />
            </DataTrigger>
        </Style.Triggers>
    </Style>
  </ComboBox.Resources>
</ComboBox>

这对我有用。

静态资源示例

     <Window.Resources>
        <x:Array x:Key="StringList" Type="System:String">
            <System:String>Line 1</System:String>
            <System:String>Line 2</System:String>
            <System:String>Line 3</System:String>
            <System:String>Line 4</System:String>
       </x:Array>       
    </Window.Resources>
    <ComboBox ItemsSource="{StaticResource StringList}" >
      <ComboBox.Resources>
        <Style TargetType="ComboBox">
            <Style.Triggers>
                <Trigger Property="SelectedItem" Value="{x:Null}">
                    <Setter Property="SelectedIndex" Value="0"/>
                </Trigger>
            </Style.Triggers>
        </Style>
    </ComboBox.Resources>
  </ComboBox>

wpf组合框默认值

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