如何显示WPF中所有子节点的treeviewItem扩展器箭头显示？

Question

I attached my problem screen shot. So refer it, i need only expand arrow icon in tree view visible to all nodes in first time Load.

Problem is that tree view items don't have children means arrow not visible . But Initial time load i need that arrow visible. After user expand it will hide.

Root have child nodes. But others not have. So Expand time only i can load.

Answer 1

This behaviour places in ControlTemplate of TreeViewItem. And there is only one way to change it - change control template of your TreeViewItem.

I used default template and style of ToggleButton and TreeViewItem.

You shoud just comment one trigger in ControlTemplate of TreeViewItem:

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

This result view: Result view

Below I paste all styles and tempaltes.

Style of ToggleButton:

<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>

ControlTemplate of TreeViewItem:

<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 of TreeViewItem:

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

Window:

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