如何实现WPF TreeView中TextBlock文本的正确自动换行？

方案1：修改TreeViewItem模板实现自动拉伸（推荐） #

默认TreeViewItem的内容区域不会自动填充可用宽度，导致TextBlock无法适配缩进后的剩余空间换行。通过自定义TreeViewItem的ControlTemplate，让内容区域占满TreeView的剩余宽度，配合TextBlock的TextWrapping="Wrap"即可实现正确换行：

<TreeView>
    <!-- 自定义TreeViewItem样式，让内容区域拉伸 -->
    <TreeView.ItemContainerStyle>
        <Style TargetType="TreeViewItem">
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="TreeViewItem">
                        <Grid>
                            <Grid.ColumnDefinitions>
                                <!-- 左侧缩进/展开按钮列 -->
                                <ColumnDefinition Width="Auto" MinWidth="19"/>
                                <!-- 内容列，占剩余全部宽度 -->
                                <ColumnDefinition Width="*"/>
                            </Grid.ColumnDefinitions>
                            <Grid.RowDefinitions>
                                <RowDefinition Height="Auto"/>
                                <RowDefinition Height="*"/>
                            </Grid.RowDefinitions>
                            
                            <ToggleButton x:Name="Expander" 
                                          ClickMode="Press" 
                                          IsChecked="{Binding IsExpanded, RelativeSource={RelativeSource TemplatedParent}}"
                                          Style="{StaticResource ExpandCollapseToggleStyle}"/>
                            
                            <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" 
                                                  ContentSource="Header" 
                                                  HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" 
                                                  SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"/>
                            </Border>
                            
                            <ItemsPresenter x:Name="ItemsHost" Grid.Column="1" Grid.Row="1"/>
                        </Grid>
                        
                        <ControlTemplate.Triggers>
                            <Trigger Property="IsExpanded" Value="false">
                                <Setter Property="Visibility" TargetName="ItemsHost" Value="Collapsed"/>
                            </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>
                </Setter.Value>
            </Setter>
        </Style>
    </TreeView.ItemContainerStyle>
    
    <!-- 你的TreeViewItem -->
    <TreeViewItem Header="Message ID">
        <TextBlock Text="The message ID determines which messages should be assigned the values in this row. This should be a hex value and applies only to the fourth byte and onwards of message data." 
                   TextWrapping="Wrap" 
                   HorizontalAlignment="Stretch"/>
    </TreeViewItem>
</TreeView>

核心逻辑是让TreeViewItem的内容列（Grid.Column="1"）设置为Width="*"，TextBlock设置HorizontalAlignment="Stretch"后会自动填充TreeView的剩余宽度，完美适配缩进，不会出现截断。

方案2：使用值转换器计算可用宽度 #

如果不想修改TreeViewItem模板，可以通过值转换器动态计算TextBlock的最大宽度（减去TreeView的缩进和内边距）：

步骤1：创建值转换器 #

using System;
using System.Globalization;
using System.Windows.Data;

namespace YourNamespace
{
    public class SubtractIndentConverter : IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            if (value is double treeViewWidth && double.TryParse(parameter?.ToString(), out double indent))
            {
                // 减去缩进值，确保最小宽度不为0
                return Math.Max(20, treeViewWidth - indent);
            }
            return value;
        }

        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        {
            throw new NotImplementedException();
        }
    }
}

步骤2：在XAML中声明转换器 #

<Window.Resources>
    <local:SubtractIndentConverter x:Key="SubtractIndentConverter"/>
</Window.Resources>

步骤3：绑定TextBlock的MaxWidth #

给TreeView命名后，绑定其ActualWidth并传入缩进参数（比如40，根据你的TreeView缩进调整）：

<TreeView x:Name="MainTreeView">
    <TreeViewItem Header="Message ID">
        <TextBlock Text="The message ID determines which messages should be assigned the values in this row. This should be a hex value and applies only to the fourth byte and onwards of message data." 
                   TextWrapping="Wrap"
                   MaxWidth="{Binding ElementName=MainTreeView, Path=ActualWidth, Converter={StaticResource SubtractIndentConverter}, ConverterParameter=40}"/>
    </TreeViewItem>
</TreeView>

可根据实际缩进大小调整ConverterParameter的值，确保文本不会被截断。

内容的提问来源于stack exchange，提问作者Joshua Banks