AvaloniaUI动态XAML绑定ExpandoObject属性不更新问题

问题根源 #

Avalonia的绑定引擎依赖静态属性元数据（反射或TypeDescriptor）解析绑定路径，而ExpandoObject的动态属性无法被该引擎正确识别，导致出现Could not find a matching property accessor错误，同时属性变更也无法被绑定系统监听。

解决方案：自定义动态属性容器 #

替换ExpandoObject为继承DynamicObject并实现INotifyPropertyChanged的自定义类，手动处理属性读写和变更通知，让Avalonia绑定系统能正确识别动态属性。

1. 创建自定义动态属性类 #

using System.ComponentModel;
using System.Dynamic;
using System.Runtime.CompilerServices;

public class DynamicPropertyBag : DynamicObject, INotifyPropertyChanged
{
    private readonly Dictionary<string, object?> _properties = new();

    public event PropertyChangedEventHandler? PropertyChanged;

    // 处理动态属性读取逻辑
    public override bool TryGetMember(GetMemberBinder binder, out object? result)
    {
        return _properties.TryGetValue(binder.Name, out result);
    }

    // 处理动态属性写入逻辑，触发变更通知
    public override bool TrySetMember(SetMemberBinder binder, object? value)
    {
        _properties[binder.Name] = value;
        OnPropertyChanged(binder.Name);
        return true;
    }

    // 提供索引器，方便绑定系统访问属性
    public object? this[string key]
    {
        get => _properties.TryGetValue(key, out var val) ? val : null;
        set
        {
            _properties[key] = value;
            OnPropertyChanged(key);
        }
    }

    private void OnPropertyChanged([CallerMemberName] string? propertyName = null)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
}

2. 更新ViewModel #

将原ExpandoObject替换为自定义的DynamicPropertyBag：

using CommunityToolkit.Mvvm.ComponentModel;
using System.Diagnostics;

namespace DynamicBindingControls.ViewModels; 

public partial class DynamicSettingsGroupVM : ViewModelBase {
  [ObservableProperty]
  private string _name;
  // 替换为自定义动态属性容器
  public dynamic DynamicSettingsProperties { get; set; } = new DynamicPropertyBag();

  public DynamicSettingsGroupVM(string aName) {
    Name = aName;
    ((INotifyPropertyChanged)DynamicSettingsProperties).PropertyChanged += HandlePropertyChanges;
  }

  private void HandlePropertyChanges(object? sender, PropertyChangedEventArgs e) {
    var bag = DynamicSettingsProperties as DynamicPropertyBag;
    Trace.WriteLine($"{e.PropertyName} has changed to {bag?[e.PropertyName]}.");
  }
}

3. 调整绑定方式 #

使用索引器语法绑定动态属性，确保Avalonia能正确解析路径：

public void CreateDynamicSettings() {
  var myDC = DataContext as ViewModels.DynamicSettingsGroupVM;

  var props = myDC.DynamicSettingsProperties as DynamicPropertyBag;
  props["DynaProp"] = "Brand new";
  // 使用索引器语法绑定动态属性
  var settingField = new TextBox {
    [!TextBox.TextProperty] = new Binding("DynamicSettingsProperties['DynaProp']")
  };

  stpDynamicFields.Children.Add(settingField);
}

验证效果 #

运行应用后：

• TextBox会正确显示初始值Brand new
• 修改TextBox内容时，调试日志会输出属性变更信息
• 绑定的双向同步功能正常工作

内容的提问来源于stack exchange，提问作者Eric Eggers