将TreeViewItem标记为可扩展，没有Items

Question

与主题一样。我想更改TreeViewItem的视图样式。没有项目箭头是不可见的。我希望在不添加任何空白项目的情况下使其可见。

Answer 1

不知道你的意思

  

不添加任何空白项目

但是，您可以添加项目，但将其Visibility设置为Collapsed：

 <TreeView>
     <TreeViewItem>
            <TextBlock Text="A"/>
     </TreeViewItem>
     <TreeViewItem>
            <TextBlock Text="A" Visibility="Collapsed"/>
     </TreeViewItem>
 </TreeView>

另一种方法：

使用this style并删除此部分：

 <Trigger Property="HasItems"
          Value="false">
          <Setter TargetName="Expander"
                  Property="Visibility"
                  Value="Hidden" />
 </Trigger>

修改

<Window x:Class="Test.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:local="clr-namespace:Test" 
    xmlns:scm="clr-namespace:System.ComponentModel;assembly=WindowsBase"
    mc:Ignorable="d"
    Title="MainWindow">

<Window.Resources>
    <Color x:Key="WindowColor">#FFE8EDF9</Color>
    <Color x:Key="ContentAreaColorLight">#FFC5CBF9</Color>
    <Color x:Key="ContentAreaColorDark">#FF7381F9</Color>

    <Color x:Key="DisabledControlLightColor">#FFE8EDF9</Color>
    <Color x:Key="DisabledControlDarkColor">#FFC5CBF9</Color>
    <Color x:Key="DisabledForegroundColor">#FF888888</Color>

    <Color x:Key="SelectedBackgroundColor">#FFC5CBF9</Color>
    <Color x:Key="SelectedUnfocusedColor">#FFDDDDDD</Color>

    <Color x:Key="ControlLightColor">White</Color>
    <Color x:Key="ControlMediumColor">#FF7381F9</Color>
    <Color x:Key="ControlDarkColor">#FF211AA9</Color>

    <Color x:Key="ControlMouseOverColor">#FF3843C4</Color>
    <Color x:Key="ControlPressedColor">#FF211AA9</Color>


    <Color x:Key="GlyphColor">#FF444444</Color>
    <Color x:Key="GlyphMouseOver">sc#1, 0.004391443, 0.002428215, 0.242281124</Color>

    <!--Border colors-->
    <Color x:Key="BorderLightColor">#FFCCCCCC</Color>
    <Color x:Key="BorderMediumColor">#FF888888</Color>
    <Color x:Key="BorderDarkColor">#FF444444</Color>

    <Color x:Key="PressedBorderLightColor">#FF888888</Color>
    <Color x:Key="PressedBorderDarkColor">#FF444444</Color>

    <Color x:Key="DisabledBorderLightColor">#FFAAAAAA</Color>
    <Color x:Key="DisabledBorderDarkColor">#FF888888</Color>

    <Color x:Key="DefaultBorderBrushDarkColor">Black</Color>

    <!--Control-specific resources.-->
    <Color x:Key="HeaderTopColor">#FFC5CBF9</Color>
    <Color x:Key="DatagridCurrentCellBorderColor">Black</Color>
    <Color x:Key="SliderTrackDarkColor">#FFC5CBF9</Color>

    <Color x:Key="NavButtonFrameColor">#FF3843C4</Color>

    <LinearGradientBrush x:Key="MenuPopupBrush"
                   EndPoint="0.5,1"
                   StartPoint="0.5,0">
        <GradientStop Color="{DynamicResource ControlLightColor}"
              Offset="0" />
        <GradientStop Color="{DynamicResource ControlMediumColor}"
              Offset="0.5" />
        <GradientStop Color="{DynamicResource ControlLightColor}"
              Offset="1" />
    </LinearGradientBrush>

    <LinearGradientBrush x:Key="ProgressBarIndicatorAnimatedFill"
                   StartPoint="0,0"
                   EndPoint="1,0">
        <LinearGradientBrush.GradientStops>
            <GradientStopCollection>
                <GradientStop Color="#000000FF"
                  Offset="0" />
                <GradientStop Color="#600000FF"
                  Offset="0.4" />
                <GradientStop Color="#600000FF"
                  Offset="0.6" />
                <GradientStop Color="#000000FF"
                  Offset="1" />
            </GradientStopCollection>
        </LinearGradientBrush.GradientStops>
    </LinearGradientBrush>
    <Style x:Key="ExpandCollapseToggleStyle"
     TargetType="ToggleButton">
        <Setter Property="Focusable"
        Value="False" />
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="ToggleButton">
                    <Grid Width="15"
            Height="13"
            Background="Transparent">
                        <VisualStateManager.VisualStateGroups>
                            <VisualStateGroup x:Name="CheckStates">
                                <VisualState x:Name="Checked">
                                    <Storyboard>
                                        <ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="(UIElement.Visibility)"
                                               Storyboard.TargetName="Collapsed">
                                            <DiscreteObjectKeyFrame KeyTime="0"
                                          Value="{x:Static Visibility.Hidden}" />
                                        </ObjectAnimationUsingKeyFrames>
                                        <ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="(UIElement.Visibility)"
                                               Storyboard.TargetName="Expanded">
                                            <DiscreteObjectKeyFrame KeyTime="0"
                                          Value="{x:Static Visibility.Visible}" />
                                        </ObjectAnimationUsingKeyFrames>
                                    </Storyboard>
                                </VisualState>
                                <VisualState x:Name="Unchecked" />
                                <VisualState x:Name="Indeterminate" />
                            </VisualStateGroup>
                        </VisualStateManager.VisualStateGroups>
                        <Path x:Name="Collapsed"
              HorizontalAlignment="Left"
              VerticalAlignment="Center"
              Margin="1,1,1,1"
              Data="M 4 0 L 8 4 L 4 8 Z">
                            <Path.Fill>
                                <SolidColorBrush Color="{DynamicResource GlyphColor}" />
                            </Path.Fill>
                        </Path>
                        <Path x:Name="Expanded"
              HorizontalAlignment="Left"
              VerticalAlignment="Center"
              Margin="1,1,1,1"
              Data="M 0 4 L 8 4 L 4 8 Z"
              Visibility="Hidden">
                            <Path.Fill>
                                <SolidColorBrush Color="{DynamicResource GlyphColor}" />
                            </Path.Fill>
                        </Path>
                    </Grid>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>
    <Style x:Key="TreeViewItemFocusVisual">
        <Setter Property="Control.Template">
            <Setter.Value>
                <ControlTemplate>
                    <Border>
                        <Rectangle Margin="0,0,0,0"
                   StrokeThickness="5"
                   Stroke="Black"
                   StrokeDashArray="1 2"
                   Opacity="0" />
                    </Border>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>
    <Style x:Key="{x:Type TreeViewItem}"
     TargetType="{x:Type TreeViewItem}">
        <Setter Property="Background"
        Value="Transparent" />
        <Setter Property="HorizontalContentAlignment"
        Value="{Binding Path=HorizontalContentAlignment,
  RelativeSource={RelativeSource AncestorType={x:Type ItemsControl}}}" />
        <Setter Property="VerticalContentAlignment"
        Value="{Binding Path=VerticalContentAlignment,
  RelativeSource={RelativeSource AncestorType={x:Type ItemsControl}}}" />
        <Setter Property="Padding"
        Value="1,0,0,0" />
        <Setter Property="Foreground"
        Value="{DynamicResource {x:Static SystemColors.ControlTextBrushKey}}" />
        <Setter Property="FocusVisualStyle"
        Value="{StaticResource TreeViewItemFocusVisual}" />
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type TreeViewItem}">
                    <Grid>
                        <Grid.ColumnDefinitions>
                            <ColumnDefinition MinWidth="19"
                            Width="Auto" />
                            <ColumnDefinition Width="Auto" />
                            <ColumnDefinition Width="*" />
                        </Grid.ColumnDefinitions>
                        <Grid.RowDefinitions>
                            <RowDefinition Height="Auto" />
                            <RowDefinition />
                        </Grid.RowDefinitions>
                        <VisualStateManager.VisualStateGroups>
                            <VisualStateGroup x:Name="SelectionStates">
                                <VisualState x:Name="Selected">
                                    <Storyboard>
                                        <ColorAnimationUsingKeyFrames Storyboard.TargetName="Bd"
                                              Storyboard.TargetProperty="(Panel.Background).
                  (SolidColorBrush.Color)"
                                              >
                                            <EasingColorKeyFrame KeyTime="0"
                                       Value="{StaticResource SelectedBackgroundColor}" />
                                        </ColorAnimationUsingKeyFrames>
                                    </Storyboard>
                                </VisualState>
                                <VisualState x:Name="Unselected" />
                                <VisualState x:Name="SelectedInactive">
                                    <Storyboard>
                                        <ColorAnimationUsingKeyFrames Storyboard.TargetName="Bd"
                                              Storyboard.TargetProperty="(Panel.Background).
                  (SolidColorBrush.Color)">
                                            <EasingColorKeyFrame KeyTime="0"
                                       Value="{StaticResource SelectedUnfocusedColor}" />
                                        </ColorAnimationUsingKeyFrames>
                                    </Storyboard>
                                </VisualState>
                            </VisualStateGroup>
                            <VisualStateGroup x:Name="ExpansionStates">
                                <VisualState x:Name="Expanded">
                                    <Storyboard>
                                        <ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="(UIElement.Visibility)"
                                               Storyboard.TargetName="ItemsHost">
                                            <DiscreteObjectKeyFrame KeyTime="0"
                                          Value="{x:Static Visibility.Visible}" />
                                        </ObjectAnimationUsingKeyFrames>
                                    </Storyboard>
                                </VisualState>
                                <VisualState x:Name="Collapsed" />
                            </VisualStateGroup>
                        </VisualStateManager.VisualStateGroups>
                        <ToggleButton x:Name="Expander"
                      Style="{StaticResource ExpandCollapseToggleStyle}"
                      ClickMode="Press"
                      IsChecked="{Binding IsExpanded, 
          RelativeSource={RelativeSource TemplatedParent}}"/>
                        <Border x:Name="Bd"
                Grid.Column="1"
                Background="{TemplateBinding Background}"
                BorderBrush="{TemplateBinding BorderBrush}"
                BorderThickness="{TemplateBinding BorderThickness}"
                Padding="{TemplateBinding Padding}">
                            <ContentPresenter x:Name="PART_Header"
                            ContentSource="Header"
                            HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"/>
                        </Border>
                        <ItemsPresenter x:Name="ItemsHost"
                        Grid.Row="1"
                        Grid.Column="1"
                        Grid.ColumnSpan="2"
                        Visibility="Collapsed" />
                    </Grid>
                    <ControlTemplate.Triggers> 
                        <MultiTrigger>
                            <MultiTrigger.Conditions>
                                <Condition Property="HasHeader"
                       Value="false" />
                                <Condition Property="Width"
                       Value="Auto" />
                            </MultiTrigger.Conditions>
                            <Setter TargetName="PART_Header"
                  Property="MinWidth"
                  Value="75" />
                        </MultiTrigger>
                        <MultiTrigger>
                            <MultiTrigger.Conditions>
                                <Condition Property="HasHeader"
                       Value="false" />
                                <Condition Property="Height"
                       Value="Auto" />
                            </MultiTrigger.Conditions>
                            <Setter TargetName="PART_Header"
                  Property="MinHeight"
                  Value="19" />
                        </MultiTrigger>
                    </ControlTemplate.Triggers>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>
</Window.Resources>

<Grid>
    <TreeView>
        <TreeViewItem>
            <TextBlock Text="A"/>
        </TreeViewItem>
        <TreeViewItem />
    </TreeView>
</Grid>
</Window>