自定义TreeViewItem设置DefaultStyleKeyProperty后无法在TreeView显示求助

问题场景 #

我创建了带自定义图片属性的TreeViewTestItem，代码如下：

class TreeViewTestItem : TreeViewItem, INotifyPropertyChanged
{
    public ImageSource _image;
    public ImageSource Image
    {
        get
        {
            return _image;
        }
        set
        {
            _image = value;
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs("Image"));
        }
    }

    static TreeViewTestItem()
    {
            DefaultStyleKeyProperty.OverrideMetadata(typeof(TreeViewTestItem), new FrameworkPropertyMetadata(typeof(TreeViewTestItem)));
    }

    public TreeViewTestItem()
    {
            PreviewMouseDown += TreeViewTestItem_PreviewMouseDown;
            _image = (ImageSource)new ImageSourceConverter().ConvertFrom(new Uri(@"pack://application:,,,/DEBUG;component/Resources/Icons/square.png"));
    }
}

在Themes/Generic.xaml中定义了对应样式：

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                    xmlns:local="clr-DEBUG.Views.Controls">

    <Style TargetType="{x:Type local:TreeViewTestItem}" BasedOn="{StaticResource {x:Type TreeViewItem}}">
        <Setter Property="HeaderTemplate">
            <Setter.Value>
                <DataTemplate>
                    <StackPanel Orientation="Horizontal" Margin="0,0,0,3">
                        <Image Source="{Binding RelativeSource={RelativeSource Mode=FindAncestor, AncestorType={x:Type local:TreeViewTestItem}}, Path=Image, Mode=TwoWay}" VerticalAlignment="Center" Width="30" Height="30" />
                        <TextBlock Text="{Binding RelativeSource={RelativeSource Mode=FindAncestor, AncestorType={x:Type TreeViewItem}}, Path=Header}" VerticalAlignment="Center" Margin="5,0,0,0" FontSize="18" />
                    </StackPanel>
                </DataTemplate>
            </Setter.Value>
        </Setter>
    </Style>
</ResourceDictionary>

TestView中TreeView绑定ViewModel的集合：

<Window x:Class="DEBUG.Views.TestView"
        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:src="clr-namespace:DEBUG.Views.Controls"
        xmlns:local="clr-namespace:DEBUG.Views"
        mc:Ignorable="d">
[...]
<TreeView ItemsSource="{Binding TreeViewTests}">
            </TreeView>
</Window>

ViewModel填充集合的代码：

class TestViewModel : MVVMHelper
{
    public ObservableCollection<TreeViewTestItem> TreeViewTests { get; set; }
    [...]
    public TestViewModel(List<Test> testList)
    {
        TreeViewTests = new ObservableCollection<TreeViewTestItem>();
    }
    private void AddTestNode(TreeViewTestItem treeItem, List<Test> testList)
    {
        foreach (Test test in testList)
            {
                TreeViewTestItem tvi = new TreeViewTestItem();
                tvi.Test = test;
                tvi.Header = test.LibelleEn;

                if (treeItem == null)
                {
                    TreeViewTests.Add(tvi);
                }
                else
                {
                    treeItem.Items.Add(tvi);
                }
                AddTestNode(tvi, test.ListeTest);
            }
    }
}

核心问题：保留TreeViewTestItem静态构造函数中的DefaultStyleKeyProperty.OverrideMetadata代码时，TreeView为空；移除后能正常显示，但自定义样式无法生效。尝试过移动自定义项位置、直接在视图中设置样式均无效，无异常抛出。

解决方案 #

1. 显式合并Generic.xaml资源字典 #

WPF自动加载Themes/Generic.xaml可能因项目结构或命名空间问题失效，可在App.xaml中显式合并：

<Application.Resources>
    <ResourceDictionary>
        <ResourceDictionary.MergedDictionaries>
            <ResourceDictionary Source="/DEBUG;component/Themes/Generic.xaml"/>
        </ResourceDictionary.MergedDictionaries>
    </ResourceDictionary>
</Application.Resources>

注意将DEBUG替换为你的实际程序集名称。

2. 修正HeaderTemplate的绑定逻辑 #

设置DefaultStyleKey后，RelativeSource查找可能失效，可直接绑定到当前TreeViewTestItem实例：

<Style TargetType="{x:Type local:TreeViewTestItem}" BasedOn="{StaticResource {x:Type TreeViewItem}}">
    <Setter Property="HeaderTemplate">
        <Setter.Value>
            <DataTemplate DataType="{x:Type local:TreeViewTestItem}">
                <StackPanel Orientation="Horizontal" Margin="0,0,0,3">
                    <Image Source="{Binding Image, Mode=TwoWay}" VerticalAlignment="Center" Width="30" Height="30" />
                    <TextBlock Text="{Binding Header}" VerticalAlignment="Center" Margin="5,0,0,0" FontSize="18" />
                </StackPanel>
            </DataTemplate>
        </Setter.Value>
    </Setter>
</Style>

通过指定DataType，让DataTemplate直接绑定到控件实例，避免查找上下文问题。

3. 检查命名空间与程序集匹配 #

确保Generic.xaml中的xmlns:local命名空间与TreeViewTestItem所在程序集完全一致。若控件命名空间为DEBUG.Views.Controls但程序集名称不同，需补充程序集信息：

xmlns:local="clr-namespace:DEBUG.Views.Controls;assembly=YourActualAssemblyName"

4. 确认样式继承完整逻辑 #

自定义样式必须通过BasedOn="{StaticResource {x:Type TreeViewItem}}"继承原生TreeViewItem的所有布局、交互逻辑，否则重写DefaultStyleKey后控件可能因缺失基础模板无法渲染。

内容的提问来源于stack exchange，提问作者Alex