C# 如何为WPF中的所有子节点显示可见的TreeViewer箭头？

我附上了我的问题截图。所以参考它，我只需要在树视图中展开箭头图标，在第一次加载时所有节点都可见

问题是树视图项没有子项意味着箭头不可见。 但初始时间负载我需要箭头可见。用户展开后，它将隐藏。

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根节点有子节点。但其他人没有。因此，只有我可以加载扩展时间。

此行为放置在TreeViewItem的ControlTemplate中。只有一种方法可以改变它——改变TreeView项目的控制模板

我使用了默认模板和ToggleButton和TreeViewItem的样式

您只需在TreeViewItem的ControlTemplate中注释一个触发器：

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

<ControlTemplate TargetType="{x:Type TreeViewItem}" x:Key="ItemTemplate">
        <Grid>
            <Grid.ColumnDefinitions>
                <ColumnDefinition MinWidth="19" Width="Auto"/>
                <ColumnDefinition Width="Auto"/>
                <ColumnDefinition Width="*"/>
            </Grid.ColumnDefinitions>
            <Grid.RowDefinitions>
                <RowDefinition Height="Auto"/>
                <RowDefinition/>
            </Grid.RowDefinitions>
            <ToggleButton x:Name="Expander" ClickMode="Press" IsChecked="{Binding IsExpanded, RelativeSource={RelativeSource TemplatedParent}}" Style="{DynamicResource TreeViewItemToggleButtonStyle}"/>
            <Border x:Name="Bd" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Background="{TemplateBinding Background}" Grid.Column="1" Padding="{TemplateBinding Padding}" SnapsToDevicePixels="True">
                <ContentPresenter x:Name="PART_Header" ContentTemplate="{TemplateBinding HeaderTemplate}" Content="{TemplateBinding Header}" ContentStringFormat="{TemplateBinding HeaderStringFormat}" ContentSource="Header" HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"/>
            </Border>
            <ItemsPresenter x:Name="ItemsHost" Grid.ColumnSpan="2" Grid.Column="1" Grid.Row="1"/>
        </Grid>
        <ControlTemplate.Triggers>
            <Trigger Property="IsExpanded" Value="False">
                <Setter Property="Visibility" TargetName="ItemsHost" Value="Collapsed"/>
            </Trigger>
            <!-- Commented trigger -->
            <!--<Trigger Property="HasItems" Value="False">
                <Setter Property="Visibility" TargetName="Expander" Value="Hidden"/>
            </Trigger>-->
            <Trigger Property="IsSelected" Value="True">
                <Setter Property="Background" TargetName="Bd" Value="{DynamicResource {x:Static SystemColors.HighlightBrushKey}}"/>
                <Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.HighlightTextBrushKey}}"/>
            </Trigger>
            <MultiTrigger>
                <MultiTrigger.Conditions>
                    <Condition Property="IsSelected" Value="True"/>
                    <Condition Property="IsSelectionActive" Value="False"/>
                </MultiTrigger.Conditions>
                <Setter Property="Background" TargetName="Bd" Value="{DynamicResource {x:Static SystemColors.InactiveSelectionHighlightBrushKey}}"/>
                <Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.InactiveSelectionHighlightTextBrushKey}}"/>
            </MultiTrigger>
            <Trigger Property="IsEnabled" Value="False">
                <Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.GrayTextBrushKey}}"/>
            </Trigger>
        </ControlTemplate.Triggers>
    </ControlTemplate>

<Style TargetType="TreeViewItem">
    <EventSetter Event="Expanded" Handler="TreeViewItem_Expanded"/>
    <Setter Property="Template" Value="{DynamicResource ItemTemplate}"/>
</Style>

此结果视图：

下面我粘贴了所有的风格和节拍

切换按钮的样式：

<Style TargetType="{x:Type ToggleButton}" x:Key="TreeViewItemToggleButtonStyle">
        <Setter Property="Focusable" Value="False"/>
        <Setter Property="Width" Value="16"/>
        <Setter Property="Height" Value="16"/>
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type ToggleButton}">
                    <Border Background="Transparent" Height="16" Padding="5" Width="16">
                        <Path x:Name="ExpandPath" Data="M0,0 L0,6 L6,0 z" Fill="White" Stroke="#FF818181">
                            <Path.RenderTransform>
                                <RotateTransform Angle="135" CenterY="3" CenterX="3"/>
                            </Path.RenderTransform>
                        </Path>
                    </Border>
                    <ControlTemplate.Triggers>
                        <Trigger Property="IsChecked" Value="True">
                            <Setter Property="RenderTransform" TargetName="ExpandPath">
                                <Setter.Value>
                                    <RotateTransform Angle="180" CenterY="3" CenterX="3"/>
                                </Setter.Value>
                            </Setter>
                            <Setter Property="Fill" TargetName="ExpandPath" Value="#FF595959"/>
                            <Setter Property="Stroke" TargetName="ExpandPath" Value="#FF262626"/>
                        </Trigger>
                        <Trigger Property="IsMouseOver" Value="True">
                            <Setter Property="Stroke" TargetName="ExpandPath" Value="#FF27C7F7"/>
                            <Setter Property="Fill" TargetName="ExpandPath" Value="#FFCCEEFB"/>
                        </Trigger>
                        <MultiTrigger>
                            <MultiTrigger.Conditions>
                                <Condition Property="IsMouseOver" Value="True"/>
                                <Condition Property="IsChecked" Value="True"/>
                            </MultiTrigger.Conditions>
                            <Setter Property="Stroke" TargetName="ExpandPath" Value="#FF1CC4F7"/>
                            <Setter Property="Fill" TargetName="ExpandPath" Value="#FF82DFFB"/>
                        </MultiTrigger>
                    </ControlTemplate.Triggers>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>

TreeViewItem的控件模板：

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

<ControlTemplate TargetType="{x:Type TreeViewItem}" x:Key="ItemTemplate">
        <Grid>
            <Grid.ColumnDefinitions>
                <ColumnDefinition MinWidth="19" Width="Auto"/>
                <ColumnDefinition Width="Auto"/>
                <ColumnDefinition Width="*"/>
            </Grid.ColumnDefinitions>
            <Grid.RowDefinitions>
                <RowDefinition Height="Auto"/>
                <RowDefinition/>
            </Grid.RowDefinitions>
            <ToggleButton x:Name="Expander" ClickMode="Press" IsChecked="{Binding IsExpanded, RelativeSource={RelativeSource TemplatedParent}}" Style="{DynamicResource TreeViewItemToggleButtonStyle}"/>
            <Border x:Name="Bd" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Background="{TemplateBinding Background}" Grid.Column="1" Padding="{TemplateBinding Padding}" SnapsToDevicePixels="True">
                <ContentPresenter x:Name="PART_Header" ContentTemplate="{TemplateBinding HeaderTemplate}" Content="{TemplateBinding Header}" ContentStringFormat="{TemplateBinding HeaderStringFormat}" ContentSource="Header" HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"/>
            </Border>
            <ItemsPresenter x:Name="ItemsHost" Grid.ColumnSpan="2" Grid.Column="1" Grid.Row="1"/>
        </Grid>
        <ControlTemplate.Triggers>
            <Trigger Property="IsExpanded" Value="False">
                <Setter Property="Visibility" TargetName="ItemsHost" Value="Collapsed"/>
            </Trigger>
            <!-- Commented trigger -->
            <!--<Trigger Property="HasItems" Value="False">
                <Setter Property="Visibility" TargetName="Expander" Value="Hidden"/>
            </Trigger>-->
            <Trigger Property="IsSelected" Value="True">
                <Setter Property="Background" TargetName="Bd" Value="{DynamicResource {x:Static SystemColors.HighlightBrushKey}}"/>
                <Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.HighlightTextBrushKey}}"/>
            </Trigger>
            <MultiTrigger>
                <MultiTrigger.Conditions>
                    <Condition Property="IsSelected" Value="True"/>
                    <Condition Property="IsSelectionActive" Value="False"/>
                </MultiTrigger.Conditions>
                <Setter Property="Background" TargetName="Bd" Value="{DynamicResource {x:Static SystemColors.InactiveSelectionHighlightBrushKey}}"/>
                <Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.InactiveSelectionHighlightTextBrushKey}}"/>
            </MultiTrigger>
            <Trigger Property="IsEnabled" Value="False">
                <Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.GrayTextBrushKey}}"/>
            </Trigger>
        </ControlTemplate.Triggers>
    </ControlTemplate>

<Style TargetType="TreeViewItem">
    <EventSetter Event="Expanded" Handler="TreeViewItem_Expanded"/>
    <Setter Property="Template" Value="{DynamicResource ItemTemplate}"/>
</Style>

TreeView项目的样式：

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

<ControlTemplate TargetType="{x:Type TreeViewItem}" x:Key="ItemTemplate">
        <Grid>
            <Grid.ColumnDefinitions>
                <ColumnDefinition MinWidth="19" Width="Auto"/>
                <ColumnDefinition Width="Auto"/>
                <ColumnDefinition Width="*"/>
            </Grid.ColumnDefinitions>
            <Grid.RowDefinitions>
                <RowDefinition Height="Auto"/>
                <RowDefinition/>
            </Grid.RowDefinitions>
            <ToggleButton x:Name="Expander" ClickMode="Press" IsChecked="{Binding IsExpanded, RelativeSource={RelativeSource TemplatedParent}}" Style="{DynamicResource TreeViewItemToggleButtonStyle}"/>
            <Border x:Name="Bd" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Background="{TemplateBinding Background}" Grid.Column="1" Padding="{TemplateBinding Padding}" SnapsToDevicePixels="True">
                <ContentPresenter x:Name="PART_Header" ContentTemplate="{TemplateBinding HeaderTemplate}" Content="{TemplateBinding Header}" ContentStringFormat="{TemplateBinding HeaderStringFormat}" ContentSource="Header" HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"/>
            </Border>
            <ItemsPresenter x:Name="ItemsHost" Grid.ColumnSpan="2" Grid.Column="1" Grid.Row="1"/>
        </Grid>
        <ControlTemplate.Triggers>
            <Trigger Property="IsExpanded" Value="False">
                <Setter Property="Visibility" TargetName="ItemsHost" Value="Collapsed"/>
            </Trigger>
            <!-- Commented trigger -->
            <!--<Trigger Property="HasItems" Value="False">
                <Setter Property="Visibility" TargetName="Expander" Value="Hidden"/>
            </Trigger>-->
            <Trigger Property="IsSelected" Value="True">
                <Setter Property="Background" TargetName="Bd" Value="{DynamicResource {x:Static SystemColors.HighlightBrushKey}}"/>
                <Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.HighlightTextBrushKey}}"/>
            </Trigger>
            <MultiTrigger>
                <MultiTrigger.Conditions>
                    <Condition Property="IsSelected" Value="True"/>
                    <Condition Property="IsSelectionActive" Value="False"/>
                </MultiTrigger.Conditions>
                <Setter Property="Background" TargetName="Bd" Value="{DynamicResource {x:Static SystemColors.InactiveSelectionHighlightBrushKey}}"/>
                <Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.InactiveSelectionHighlightTextBrushKey}}"/>
            </MultiTrigger>
            <Trigger Property="IsEnabled" Value="False">
                <Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.GrayTextBrushKey}}"/>
            </Trigger>
        </ControlTemplate.Triggers>
    </ControlTemplate>

<Style TargetType="TreeViewItem">
    <EventSetter Event="Expanded" Handler="TreeViewItem_Expanded"/>
    <Setter Property="Template" Value="{DynamicResource ItemTemplate}"/>
</Style>

窗口：

<Grid>
    <TreeView>
        <TreeViewItem Header="Root" IsExpanded="True">
            <TreeViewItem Header="Inner 1"/>
            <TreeViewItem Header="Inner 2"/>
        </TreeViewItem>
    </TreeView>
</Grid>