我有一个自定义INotifyCollectionChanged
类,它基本上只包含标准ObservableCollection
。每当添加/删除某些内容时,CollectionChanged
事件都会按预期引发。但是,当我尝试使用WeakEventListener
侦听此事件时,侦听器永远不会收到该事件。为什么会发生这种情况?如何解决这个问题?
在下面的示例中,我希望抛出NotImplementedException
,但测试用例成功(这清楚地表明事件真的被提升)。如果您将集合更改为ObservableCollection
而不是Wrapper
,则会按预期抛出异常。
public class Test : IWeakEventListener
{
private class Wrapper : INotifyCollectionChanged
{
private readonly ObservableCollection<string> _internal
= new ObservableCollection<string>();
public void Add(string s)
{
_internal.Add(s);
}
public event NotifyCollectionChangedEventHandler CollectionChanged
{
add { _internal.CollectionChanged += value; }
remove { _internal.CollectionChanged -= value; }
}
}
public bool ReceiveWeakEvent(Type managerType, object sender, EventArgs e)
{
throw new NotImplementedException();
}
[Test]
public void CustomCollectionTest()
{
//change to new ObservableCollection<string>() and the exception gets thrown
var collection = new Wrapper();
var raised = false;
collection.CollectionChanged += (o, e) => raised = true;
CollectionChangedEventManager.AddListener(collection, this);
collection.Add("foobar");
Assert.True(raised);
}
}
可能相关但仍然没有答案:
Why WeakEventManager does not fire an event when the sender is not the nominal?
答案 0 :(得分:1)
至于原因,问题与this question中的问题相同。从本质上讲,在事件管理器中注册的源必须与事件的发送者相同。
作为此限制的解决方法,我只需要确保Wrapper
发送事件,而不是直接在包装集合上使用事件。
private class Wrapper : INotifyCollectionChanged
{
private readonly ObservableCollection<string> _internal
= new ObservableCollection<string>();
public Wrapper()
{
_internal.CollectionChanged += OnInternalChanged;
}
public void Add(string s)
{
_internal.Add(s);
}
private void OnInternalChanged(object sender, NotifyCollectionChangedEventArgs e)
{
var toRaise = CollectionChanged;
if (toRaise != null)
toRaise(this, e);
}
public event NotifyCollectionChangedEventHandler CollectionChanged;
}