模板组合框的“默认”文本

Question

我有一个基于数据模板的组合框，其中包含如下复选框：

    <ComboBox x:Name="cboComplex" Text="Select days...">
        <ComboBox.ItemTemplate>
            <DataTemplate>
                <StackPanel Orientation="Horizontal">
                    <CheckBox IsChecked="{Binding Path=IsSelected}" Width="20"/>
                    <TextBlock Text="{Binding DayOfWeek}" Width="100" />
                 </StackPanel>
            </DataTemplate>

        </ComboBox.ItemTemplate>
    </ComboBox>

我遇到的问题是我希望组合框显示“选择日期...”，然后在单击时显示列表。不幸的是，设置 Text 属性似乎没有效果。任何想法或帮助将不胜感激。

提前致谢！

西格

Answer 1

当 ComboBox 可编辑时使用 Text 属性。您可以通过向 ControlTemplate 添加一个元素来设置默认的“选择”类型消息，该元素仅在没有选择时显示然后消失。使用此方法，您无需担心修改您的集合或让用户尝试从列表中选择“选择”消息，因为它不是列表的一部分。我建议使用标签在每个实例或样式中设置您的消息，然后添加一个新的 TextBlock 以将其显示到默认模板中：

<TextBlock x:Name="SelectMessage" HorizontalAlignment="Left" Text="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=Tag}" VerticalAlignment="Center" Margin="{TemplateBinding Padding}" Visibility="Collapsed"/>

那么你可以这样使用它：

<ComboBox ItemsSource="{Binding MyList}" Template="{StaticResource ComboBoxMessageTemplate}" Tag="Select days..."/>

这是默认 Aero ComboBox 模板的完整 Blend 生成副本，其中包含更改。您还需要主题命名空间 (xmlns:Microsoft_Windows_Themes="clr-namespace:Microsoft.Windows.Themes;assembly=PresentationFramework.Aero") 和对 PresentationFramework.Aero 程序集的引用：

<Geometry x:Key="DownArrowGeometry">M 0 0 L 3.5 4 L 7 0 Z</Geometry>
<Style x:Key="ComboBoxReadonlyToggleButton" TargetType="{x:Type ToggleButton}">
    <Setter Property="OverridesDefaultStyle" Value="true"/>
    <Setter Property="IsTabStop" Value="false"/>
    <Setter Property="Focusable" Value="false"/>
    <Setter Property="ClickMode" Value="Press"/>
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="{x:Type ToggleButton}">
                <Microsoft_Windows_Themes:ButtonChrome x:Name="Chrome" SnapsToDevicePixels="true" Background="{TemplateBinding Background}" BorderBrush="{TemplateBinding BorderBrush}" RenderMouseOver="{TemplateBinding IsMouseOver}" RenderPressed="{TemplateBinding IsPressed}">
                    <Grid HorizontalAlignment="Right" Width="{DynamicResource {x:Static SystemParameters.VerticalScrollBarWidthKey}}">
                        <Path x:Name="Arrow" Fill="Black" HorizontalAlignment="Center" Margin="3,1,0,0" VerticalAlignment="Center" Data="{StaticResource DownArrowGeometry}"/>
                    </Grid>
                </Microsoft_Windows_Themes:ButtonChrome>
                <ControlTemplate.Triggers>
                    <Trigger Property="IsChecked" Value="true">
                        <Setter Property="RenderPressed" TargetName="Chrome" Value="true"/>
                    </Trigger>
                    <Trigger Property="IsEnabled" Value="false">
                        <Setter Property="Fill" TargetName="Arrow" Value="#AFAFAF"/>
                    </Trigger>
                </ControlTemplate.Triggers>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>

<ControlTemplate x:Key="ComboBoxMessageTemplate" TargetType="{x:Type ComboBox}">
    <Grid x:Name="MainGrid" SnapsToDevicePixels="true">
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="*"/>
            <ColumnDefinition MinWidth="{DynamicResource {x:Static SystemParameters.VerticalScrollBarWidthKey}}" Width="0"/>
        </Grid.ColumnDefinitions>
        <Popup x:Name="PART_Popup" Margin="1" AllowsTransparency="true" IsOpen="{Binding IsDropDownOpen, RelativeSource={RelativeSource TemplatedParent}}" Placement="Bottom" PopupAnimation="{DynamicResource {x:Static SystemParameters.ComboBoxPopupAnimationKey}}" Grid.ColumnSpan="2">
            <Microsoft_Windows_Themes:SystemDropShadowChrome x:Name="Shdw" MaxHeight="{TemplateBinding MaxDropDownHeight}" MinWidth="{Binding ActualWidth, ElementName=MainGrid}" Color="Transparent">
                <Border x:Name="DropDownBorder" Background="{DynamicResource {x:Static SystemColors.WindowBrushKey}}" BorderBrush="{DynamicResource {x:Static SystemColors.WindowFrameBrushKey}}" BorderThickness="1">
                    <ScrollViewer CanContentScroll="true">
                        <ItemsPresenter SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" KeyboardNavigation.DirectionalNavigation="Contained"/>
                    </ScrollViewer>
                </Border>
            </Microsoft_Windows_Themes:SystemDropShadowChrome>
        </Popup>
        <ToggleButton Style="{StaticResource ComboBoxReadonlyToggleButton}" Background="{TemplateBinding Background}" BorderBrush="{TemplateBinding BorderBrush}" Grid.ColumnSpan="2" IsChecked="{Binding IsDropDownOpen, Mode=TwoWay, RelativeSource={RelativeSource TemplatedParent}}"/>
        <ContentPresenter HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" Margin="{TemplateBinding Padding}" VerticalAlignment="{TemplateBinding VerticalContentAlignment}" IsHitTestVisible="false" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" Content="{TemplateBinding SelectionBoxItem}" ContentStringFormat="{TemplateBinding SelectionBoxItemStringFormat}" ContentTemplate="{TemplateBinding SelectionBoxItemTemplate}" ContentTemplateSelector="{TemplateBinding ItemTemplateSelector}"/>
        <TextBlock x:Name="SelectMessage" HorizontalAlignment="Left" Text="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=Tag}" VerticalAlignment="Center" Margin="{TemplateBinding Padding}" Visibility="Collapsed"/>
    </Grid>
    <ControlTemplate.Triggers>
        <Trigger Property="SelectedItem" Value="{x:Null}">
            <Setter Property="Visibility" TargetName="SelectMessage" Value="Visible"/>
        </Trigger>
        <Trigger Property="HasDropShadow" SourceName="PART_Popup" Value="true">
            <Setter Property="Margin" TargetName="Shdw" Value="0,0,5,5"/>
            <Setter Property="Color" TargetName="Shdw" Value="#71000000"/>
        </Trigger>
        <Trigger Property="HasItems" Value="false">
            <Setter Property="Height" TargetName="DropDownBorder" Value="95"/>
        </Trigger>
        <Trigger Property="IsEnabled" Value="false">
            <Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.GrayTextBrushKey}}"/>
            <Setter Property="Background" Value="#FFF4F4F4"/>
        </Trigger>
        <Trigger Property="IsGrouping" Value="true">
            <Setter Property="ScrollViewer.CanContentScroll" Value="false"/>
        </Trigger>
    </ControlTemplate.Triggers>
</ControlTemplate>

Answer 2

在组合框中显示默认文本

 <ComboBox Height="23" HorizontalAlignment="Left" Margin="180,18,0,0" Name="cmbExportData" VerticalAlignment="Top" Width="148" ItemsSource="{Binding}" Text="-- Select Value --" AllowDrop="False" IsEditable="True" IsManipulationEnabled="False" IsReadOnly="True" />

• 设置组合框的文本属性
• 标记为IsEditable = true
• 标记为IsReadOnly = true

Answer 3

您必须在基础集合类中创建一个新项目，其值为“Select Days...”，索引 [0] 并将所选索引更改为 0。

    <ComboBox x:Name="cboComplex" SelectedIndex="0">
        <ComboBox.ItemTemplate>
            <DataTemplate>
                <StackPanel Orientation="Horizontal">
                    <CheckBox IsChecked="{Binding Path=IsSelected}" Width="20"/>
                    <TextBlock Text="{Binding DayOfWeek}" Width="100" />
                 </StackPanel>
            </DataTemplate>

        </ComboBox.ItemTemplate>
    </ComboBox>

或者另一种选择是在其上放置一个带有文本“Select Days...”的标签，然后监听 OnSelectionChanged 事件，如果 SelectedIndex 不是 -1，则将标签可见性更改为 false，否则为真。例如

    private void MyListBox_SelectionChanged(object sender, SelectionChangedEventArgs e)
    {
        if (MyListBox.SelectedIndex >= 0)
        {
            MyListBoxInitialLabel.Visibility = Visibility.Hidden;
        }
        else
        {
            MyListBoxInitialLabel.Visibility = Visibility.Visible;
        }
    }