爲什麼我的RoutedEvent使用DependencyProperty的舊值？

Question

我需要提出更改UserControl（稱爲MenuButton）的DP（稱爲CurrentItem）值的事件以通知另一個UserControl更改其Title DP。一切正常，但舊值的CurrentItem用於目標DP。我如何強制它使用CurrentItem DP的新值？

---

public partial class MenuButton : UserControl 
{ 
    ... 

    public struct ZoneMenuItem 
    { 
     public string MenuTitle 
     { 
      get; 
      set; 
     } 

     public string ZoneTitle 
     { 
      get; 
      set; 
     } 

     public ZoneMenuItem(string menuTitle, string zoneTitle) 
     { 
      this = new ZoneMenuItem(); 

      this.MenuTitle = menuTitle; 
      this.ZoneTitle = zoneTitle; 
     } 
    } 

    #region ________________________________________ CurrentItemChanged RoutedEvent 

    public event RoutedEventHandler CurrentItemChanged 
    { 
     add { AddHandler(CurrentItemChangedEvent, value); } 
     remove { RemoveHandler(CurrentItemChangedEvent, value); } 
    } 

    public static readonly RoutedEvent CurrentItemChangedEvent = 
     EventManager.RegisterRoutedEvent("CurrentItemChanged", RoutingStrategy.Direct, typeof(RoutedEventHandler), typeof(MenuButton)); 

    #endregion 

    #region ________________________________________ CurrentItem DependencyProperty 

    public ZoneMenuItem CurrentItem 
    { 
     get { return (ZoneMenuItem)GetValue(CurrentItemProperty); } 
     set { SetValue(CurrentItemProperty, value); } 
    } 

    public static readonly DependencyProperty CurrentItemProperty = 
     DependencyProperty.Register("CurrentItem", 
            typeof(ZoneMenuItem), 
            typeof(MenuButton), 
            new FrameworkPropertyMetadata(new ZoneMenuItem(), FrameworkPropertyMetadataOptions.None, OnCurrentItemPropertyChanged)); 

    private static void OnCurrentItemPropertyChanged(DependencyObject sender, DependencyPropertyChangedEventArgs e) 
    { 
     MenuButton instance = sender as MenuButton; 

     if (instance != null) 
     { 
      instance.RaiseEvent(new RoutedEventArgs(MenuButton.CurrentItemChangedEvent)); 
     } 
    } 

    #endregion 
} 

如上所示，我上CurrentItem屬性改變引發的事件。它在另一個用戶控件使用像這樣：

<i:EventTrigger SourceName="menuButton" EventName="CurrentItemChanged"> 
    <ei:ChangePropertyAction TargetObject="{Binding}" PropertyName="Title"> 
     <ei:ChangePropertyAction.Value> 
      <Binding ElementName="menuButton" Path="CurrentItem.ZoneTitle"/> 
     </ei:ChangePropertyAction.Value> 
    </ei:ChangePropertyAction> 
</i:EventTrigger> 

其中

xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity" 
xmlns:ei="http://schemas.microsoft.com/expression/2010/interactions" 

---

更新1：

我通過使用代碼隱藏，而不是找到了一個解決方法是利用交互觸發。 （爲什麼它的工作？！）

menuButton.CurrentItemChanged += menuButton_CurrentItemChanged; 


private void menuButton_CurrentItemChanged(object sender, RoutedEventArgs e) 
{ 
    this.Title = (sender as MenuButton).CurrentItem.ZoneTitle; 
} 

---

更新2：

我試圖用一個EventTrigger只做所有任務在XAML，但它的行爲完全一樣一個交互觸發器！

<vc:MenuButton x:Name="menuButton" VerticalAlignment="Center" Margin="3,3,0,0"> 
    <vc:MenuButton.Triggers> 
     <EventTrigger SourceName="menuButton" RoutedEvent="vc:MenuButton.CurrentItemChanged"> 
      <BeginStoryboard> 
       <Storyboard> 
        <StringAnimationUsingKeyFrames Storyboard.Target="{Binding}" Storyboard.TargetProperty="Title"> 
         <DiscreteStringKeyFrame KeyTime="0" Value="{Binding ElementName=menuButton, Path=CurrentItem.ZoneTitle}"/> 
        </StringAnimationUsingKeyFrames> 
       </Storyboard> 
      </BeginStoryboard> 
     </EventTrigger> 
    </vc:MenuButton.Triggers> 
</vc:MenuButton> 

這太奇怪了！爲什麼這些觸發器具有與事件處理程序不同的行爲？

Answer 1

如果我沒有忽視其他，那麼原因可能是因爲結構是按值傳遞的。這個原因有兩個副本。一個用於你的綁定和其他原始的綁定。這意味着，如果你的綁定更新了內存中的結構而不是原來的結構。