模板组合框的“默认”文本 [英] 'Default' text for templated combo box

问题描述

我有一个基于数据模板的组合框，其中包含如下复选框：

I have a combo box that is based on a data template the includes check boxes like such:

    <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，我想让组合框显示选择天.. 。，然后单击时显示列表。不幸的是，设置Text属性似乎没有效果。任何想法或帮助将非常感谢。

The problem I'm having is that I'd like the combobox to display "Select days..." and then show the list when clicked. Unfortunately setting the Text property seems to have no effect. Any ideas or help would be greatly appreciated.

提前感谢！

Sieg

推荐答案

当ComboBox是可编辑的时，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，该元素只有在没有选择时才显示，然后消失。使用此方法，您不需要担心修改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将其显示为默认模板：

The Text property is used when the ComboBox is editable. You can set a default "Select" type message by adding an element to the ControlTemplate that shows up only when there is no selection and then disappears. Using this method you don't need to worry about modifying your collection or having a user try to pick the "Select" message from the list because it isn't part of the list. I'd recommend using the Tag to set your message on each instance or in a Style and then adding a new TextBlock to display it into the default template:

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

然后你可以这样使用：

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

这是一个完整的Blend生成的默认Aero ComboBox模板的副本与更改。你还需要主题命名空间（xmlns：Microsoft_Windows_Themes =clr-namespace：Microsoft.Windows.Themes; assembly = PresentationFramework.Aero）和PresentationFramework.Aero程序集的引用：

Here's a complete Blend generated copy of the default Aero ComboBox template with the changes. You'll also need the theme namespace (xmlns:Microsoft_Windows_Themes="clr-namespace:Microsoft.Windows.Themes;assembly=PresentationFramework.Aero") and a reference to the PresentationFramework.Aero assembly:

<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>

这篇关于模板组合框的“默认”文本的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！