如何將事件處理程序委託轉換爲具有不同簽名的事件處理程序代理

Question

我正在編寫的代碼實際上是一種WPF行爲，用於從網格控件（SelectedItems，因爲我們知道，它不是可綁定屬性）中獲取所選項目。我實際上使用Telerik RadGridView，但我希望行爲對於任何具有SelectionChanged事件的事件來說都是通用的。但是，不同的控件對SelectionChanged事件處理程序具有不同的簽名（RadGridView使用Telerik.Windows.Controls.SelectionChangeEventArgs，而標準的GridView使用System.Windows.Controls.SelectionChangedEventArgs）。我們可以確定的一件事是事件參數將來自EventArgs（實際上我們可以確定它將從RoutedEventArgs派生）。然而，雖然我可以編寫一個將RoutedEventArgs作爲其第二個參數的常規事件處理程序，但是我可以使用反射來獲取SelectionChangedEvent的EventInfo，但是我無法使用精確性將該處理程序掛接到該事件事件處理程序的簽名 - 在本例中爲RadGridView處理程序。

這是我的代碼。我已經包含了所有內容，但重要的是SelectItemPropertyChanged，它是DependencyObject PropertyChangedCallback，它嘗試將事件處理程序SelectionChangedHandler連接到SelectionChangedEvent。 （SelectionChangedHandler中的代碼與這個問題無關，但我已經將它留在了這裏，這很清楚我在做什麼）。

public static class SelectedItemsChangedBehaviour{ 
public static readonly DependencyProperty SelectItemsProperty = 
    DependencyProperty.RegisterAttached("SelectItems", typeof(bool), typeof(SelectedItemsChangedBehaviour), 
    new FrameworkPropertyMetadata(false, new PropertyChangedCallback(SelectItemPropertyChanged))); 

public static void SetSelectItems(DependencyObject dependencyObject, bool selectItems) 
{ 
    dependencyObject.SetValue(SelectItemsProperty, selectItems); 
} 

public static bool GetSelectItems(DependencyObject dependencyObject) 
{ 
    return (bool)dependencyObject.GetValue(SelectItemsProperty); 
} 

private static void SelectItemPropertyChanged(DependencyObject dependencyObject, DependencyPropertyChangedEventArgs dependencyPropertyChangedEventArgs) 
{ 
    // No common base for all classes with SelectionChanged event so use reflection 
    EventInfo selectionChangedEventInfo = dependencyObject.GetType().GetEvent("SelectionChanged"); 
    if (selectionChangedEventInfo == null) 
    { 
     throw new ArgumentException("Must have a SelectionChanged event."); 
    } 

    if ((bool)dependencyPropertyChangedEventArgs.OldValue) 
    { 
     // This is what I want to do, but it throws because the handler signature is wrong 
     selectionChangedEventInfo.RemoveEventHandler(dependencyObject, (RoutedEventHandler)SelectionChangedHandler); 

     // This works fine because it is of the right type for the RadGridView but is not general 
     //selectionChangedEventInfo.RemoveEventHandler(dependencyObject, (EventHandler<Telerik.Windows.Controls.SelectionChangeEventArgs>)SelectionChangedHandler); 
    } 
    if ((bool)dependencyPropertyChangedEventArgs.NewValue) 
    { 
     // This is what I want to do, but it throws because the handler signature is wrong 
     selectionChangedEventInfo.AddEventHandler(dependencyObject, (RoutedEventHandler)SelectionChangedHandler); 

     // This works fine because it is of the right type for the RadGridView but is not general 
     //selectionChangedEventInfo.AddEventHandler(dependencyObject, (EventHandler<Telerik.Windows.Controls.SelectionChangeEventArgs>)SelectionChangedHandler); 
    } 
} 

private static void SelectionChangedHandler(object sender, RoutedEventArgs eventArgs) 
{ 
    // No common base for all classes with AddedItems/RemovedItems (eg. System.Windows.Controls.SelectionChangedEventArgs/Telerik.Windows.Controls.SelectionChangeEventArgs 
    PropertyInfo addedItemsInfo = eventArgs.GetType().GetProperty("AddedItems"); 
    PropertyInfo removedItemsInfo = eventArgs.GetType().GetProperty("RemovedItems"); 
    if (addedItemsInfo == null || removedItemsInfo == null) 
    { 
     throw new ArgumentException("Must have AddedItems and RemovedItems"); 
    } 
    foreach (object item in (IEnumerable)addedItemsInfo.GetValue(eventArgs, null)) 
    { 
     ((ISelectable)item).IsSelected = true; 
    } 
    foreach (object item in (IEnumerable)removedItemsInfo.GetValue(eventArgs, null)) 
    { 
     ((ISelectable)item).IsSelected = false; 
    } 
} 

我已經嘗試了各種方法來使用反射來獲取正確的簽名的該處理程序，從而創建一個委託到正確的類型，但我不能讓它工作 - 的addEventHandler（和RemoveEventHandler）拋出InvalidArgumentException，全堆棧跟蹤，如下所示：

{「類型‘System.Windows.RoutedEventHandler’的對象不能被轉換爲類型‘System.EventHandler`1 [Telerik.Windows.Controls.SelectionChangeEventArgs]’ 。「}

at System.RuntimeType.TryChangeType（Object value，Binder binder，CultureInfo culture，Boolea n needsSpecialCast）

有誰能提醒？

Answer 1

調用AddEventHandler時，需要將代表轉換爲事件的EventHandlerType。這裏有一個示例應用程序：

using System; 
using System.Reflection; 
using System.Threading; 

namespace App 
{ 
    class Program 
    { 
     public event EventHandler<ThreadExceptionEventArgs> E; 

     static void Main() 
     { 
      new Program().Run(); 
     } 

     private void Run() 
     { 
      EventInfo e = typeof(Program).GetEvent("E"); 
      EventHandler untypedHandler = OnE; 
      Delegate typedHandler = Delegate.CreateDelegate(e.EventHandlerType, 
       untypedHandler.Target, untypedHandler.Method); 
      e.AddEventHandler(this, typedHandler); 
      E(this, new ThreadExceptionEventArgs(new Exception("Hello world!"))); 
     } 

     private void OnE (object sender, EventArgs args) 
     { 
      Console.WriteLine(((ThreadExceptionEventArgs)args).Exception.Message); 
     } 
    } 
}