如何编写可以承载可变数量的子属性/元素/xaml 标签的行为

如何解决如何编写可以承载可变数量的子属性/元素/xaml 标签的行为

我创建了一个需要接收可变数量输入的 Interaction.Behavior 行为。

为此，该行为有一个 List<> Dependency 属性来接收内容：

private static readonly DependencyPropertyKey FocusTargetsPropertyKey = DependencyProperty.RegisterReadOnly("Targets",typeof(List<FocusTarget>),typeof(StatefulFocusManagerBehavior),new PropertyMetadata(new List<FocusTarget>()));

public static readonly DependencyProperty FocusTargetsProperty = FocusTargetsPropertyKey.DependencyProperty;

public List<FocusTarget> Targets
{
    get => (List<FocusTarget>)this.GetValue(FocusTargetsProperty);
    set => this.SetValue(FocusTargetsProperty,value);
}

并且内容是作为派生自 FocusTarget 的类 FrameworkElement 实现的：

public class FocusTarget : FrameworkElement
{
    
    #region DepProp: FocusTarget

    public static readonly DependencyProperty FocusTargetProperty = DependencyProperty.Register("Target",typeof(FrameworkElement),typeof(FocusTarget),new PropertyMetadata(null));

    public FrameworkElement Target
    {
        get => (FrameworkElement)this.GetValue(FocusTargetProperty);
        set => this.SetValue(FocusTargetProperty,value);
    }

    #endregion

    #region DepProp: StateName

    public static readonly DependencyProperty StateNameProperty = DependencyProperty.Register("StateName",typeof(string),new PropertyMetadata(null));

    public string StateName
    {
        get => (string)this.GetValue(StateNameProperty);
        set => this.SetValue(StateNameProperty,value);
    }

    #endregion
}

行为声明如下：

<b:Interaction.Behaviors>
    <behav:StatefulFocusManagerBehavior FocusTarget="{Binding ElementName=txtResponse}">
        <behav:StatefulFocusManagerBehavior.Targets>
            <behav:FocusTarget Target="{Binding ElementName=txtResponse}"  StateName="Text"  />
            <behav:FocusTarget Target="{Binding ElementName=QnAToggle}"    StateName="Toggle"/>
        </behav:StatefulFocusManagerBehavior.Targets>
    </behav:StatefulFocusManagerBehavior>
</b:Interaction.Behaviors>

现在是有效的：

• behav:StatefulFocusManagerBehavior 的 FocusTarget 属性绑定按预期工作
• behav:FocusTarget 实例的属性 StateName 已按预期设置
• behav:FocusTarget 实例的 Target 属性始终设置为 null

我确实怀疑这可能是 DataContext 问题，但无法验证或排除它，让我对可能的问题和解决方案感到困惑。

我尝试设置 DataContext，但此绑定不起作用并给我空值：

<behav:FocusTarget Target="{Binding ElementName=txtResponse}"   
                   StateName="Text"
                   DataContext="{Binding DataContext,RelativeSource={RelativeSource AncestorType=UserControl}}"  />

解决方法

从行为集合继承数据上下文和访问元素不会这样，因为集合不在可视化树中，也不是启用绑定的 FrameworkElement 或 Freezable。

将 FocusTargetsProperty 更改为 FreezableCollection<FocusTarget> 而不是 List<FocusTarget>。此外，请确保在构造函数中分配集合的新实例。

public class StatefulFocusManagerBehavior : Behavior<FrameworkElement>
{
   private static readonly DependencyPropertyKey FocusTargetsPropertyKey = DependencyProperty.RegisterReadOnly("Targets",typeof(FreezableCollection<FocusTarget>),typeof(StatefulFocusManagerBehavior),new PropertyMetadata(null));

   public static readonly DependencyProperty FocusTargetsProperty = FocusTargetsPropertyKey.DependencyProperty;

   public FreezableCollection<FocusTarget> Targets
   {
      get => (FreezableCollection<FocusTarget>)this.GetValue(FocusTargetsProperty);
      set => this.SetValue(FocusTargetsProperty,value);
   }

   public StatefulFocusManagerBehavior()
   {
      SetValue(FocusTargetsPropertyKey,new FreezableCollection<FocusTarget>());
   }
}

然后，不是从 FrameworkElement 中的 FocusTarget 继承，而是从 Freezable 派生。

public class FocusTarget : Freezable
{
   protected override Freezable CreateInstanceCore()
   {
      return new FocusTarget();
   }

   // ...your other code.
}