Avalonia TreeDataGrid如何将HierarchicalExpanderColumn中ToggleButton点击区域扩至整单元格？

方法1：自定义CellTemplate，让ToggleButton占满单元格 #

直接替换HierarchicalExpanderColumn的CellTemplate，用布局容器包裹HierarchicalExpander，让内部切换按钮拉伸至整个单元格，同时保留层级缩进效果：

<TreeDataGrid.Columns>
    <HierarchicalExpanderColumn
        Header="Name"
        ItemsPath="Children">
        <HierarchicalExpanderColumn.CellTemplate>
            <DataTemplate>
                <Grid>
                    <!-- 用Margin模拟层级缩进，对应TreeDataGrid的默认缩进逻辑 -->
                    <HierarchicalExpander
                        Margin="{Binding Level, Converter={StaticResource LevelToIndentConverter}}"
                        HorizontalAlignment="Stretch"
                        VerticalAlignment="Stretch"
                        IsExpanded="{Binding IsExpanded}"
                        ItemsSource="{Binding Children}">
                        <HierarchicalExpander.Template>
                            <ControlTemplate>
                                <ToggleButton
                                    HorizontalAlignment="Stretch"
                                    VerticalAlignment="Stretch"
                                    IsChecked="{TemplateBinding IsExpanded}"
                                    Template="{StaticResource HierarchicalExpanderToggleButtonTemplate}">
                                    <!-- 单元格内容，示例为文本 -->
                                    <TextBlock Text="{Binding Name}" />
                                </ToggleButton>
                            </ControlTemplate>
                        </HierarchicalExpander.Template>
                    </HierarchicalExpander>
                </Grid>
            </DataTemplate>
        </HierarchicalExpanderColumn.CellTemplate>
    </HierarchicalExpanderColumn>
</TreeDataGrid.Columns>

注：LevelToIndentConverter是自定义转换器，根据节点层级计算缩进值，比如每层增加20px左外边距

方法2：利用单元格事件冒泡触发切换 #

给TreeDataGrid添加CellPointerPressed事件，在事件处理中找到对应单元格的HierarchicalExpander，主动触发切换逻辑：

private void TreeDataGrid_CellPointerPressed(object sender, PointerPressedEventArgs e)
{
    var cell = e.Source as DataGridCell;
    if (cell?.DataContext is YourTreeNodeViewModel node)
    {
        var expander = cell.FindDescendantOfType<HierarchicalExpander>();
        if (expander != null)
        {
            expander.IsExpanded = !expander.IsExpanded;
            e.Handled = true;
        }
    }
}

同时在XAML中绑定事件：

<TreeDataGrid CellPointerPressed="TreeDataGrid_CellPointerPressed" ... />

方法3：重写HierarchicalExpander的默认样式 #

修改HierarchicalExpander的默认控件模板，让内部切换按钮占满整个控件空间，消除多余间距：

<Style TargetType="HierarchicalExpander">
    <Setter Property="Template">
        <ControlTemplate TargetType="HierarchicalExpander">
            <ToggleButton
                HorizontalAlignment="Stretch"
                VerticalAlignment="Stretch"
                IsChecked="{TemplateBinding IsExpanded}"
                Padding="0">
                <Grid>
                    <Grid.ColumnDefinitions>
                        <ColumnDefinition Width="Auto" />
                        <ColumnDefinition Width="*" />
                    </Grid.ColumnDefinitions>
                    <!-- 展开/折叠图标 -->
                    <Path
                        Grid.Column="0"
                        Data="{StaticResource TreeArrow}"
                        Margin="0 2"
                        Width="12"
                        Height="12"
                        Fill="{TemplateBinding Foreground}"
                        RenderTransformOrigin="0.5,0.5">
                        <Path.RenderTransform>
                            <RotateTransform Angle="{Binding IsExpanded, RelativeSource={RelativeSource TemplatedParent}, Converter={StaticResource BooleanToAngleConverter}}" />
                        </Path.RenderTransform>
                    </Path>
                    <!-- 内容区域 -->
                    <ContentPresenter
                        Grid.Column="1"
                        Margin="4 0 0 0"
                        HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"
                        VerticalAlignment="{TemplateBinding VerticalContentAlignment}"
                        Content="{TemplateBinding Content}" />
                </Grid>
            </ToggleButton>
        </ControlTemplate>
    </Setter>
</Style>

该样式让ToggleButton完全覆盖HierarchicalExpander区域，点击单元格内任意位置都会触发切换。

内容的提问来源于stack exchange，提问作者Tobias Rieper