C# WeakEventManager保留对订阅服务器的引用
我一直在使用WeakEventManager来避免内存泄漏,并开始过度使用它们。 我为INotifyPropertyChanged创建了扩展方法,例如:C# WeakEventManager保留对订阅服务器的引用,c#,closures,weakeventmanager,C#,Closures,Weakeventmanager,我一直在使用WeakEventManager来避免内存泄漏,并开始过度使用它们。 我为INotifyPropertyChanged创建了扩展方法,例如: public static void AddWeakPropertyChanged(this INotifyPropertyChanged item, Action handler) { PropertyChangedEventManager.AddHandler(item, (s, e) => handler(e.PropertyN
public static void AddWeakPropertyChanged(this INotifyPropertyChanged item, Action handler)
{
PropertyChangedEventManager.AddHandler(item, (s, e) => handler(e.PropertyName), string.Empty);
}
现在我很快意识到,这是行不通的。事实上,您不能真正使用匿名方法来处理弱事件。(如果我理解正确,那么编译器会为它创建一个“闭包类”(用来保存引用的值),该类具有处理程序,但由于您的闭包类没有在任何地方被引用,因此GC会将其清除,并且不会调用事件处理程序)
问题1:对吗?我的意思是,如果对弱事件处理程序使用匿名方法(或lambda),则仅当GC没有同时运行时才调用该处理程序(例如,它是不确定的)
嗯,我想是的,所以我做了一些单元测试来确保我做对了。在我进行以下单元测试之前,似乎一切正常:
class DidRun
{
public bool Value { get; set; }
}
class TestEventPublisher
{
public event EventHandler<EventArgs> MyEvent;
public void RaiseMyEvent()
{
if (MyEvent != null)
MyEvent(this, EventArgs.Empty);
}
}
class TestClosure
{
public DidRun didRun { get; set; }
public EventHandler<EventArgs> Handler { get; private set; }
public TestClosure()
{
this.Handler = new EventHandler<EventArgs>((s, e) => didRun.Value = true);
}
}
[TestMethod]
public void TestWeakReference()
{
var raiser = new TestEventPublisher();
var didrun = new DidRun();
var closure = new TestClosure { didRun = didrun };
WeakEventManager<TestEventPublisher, EventArgs>.AddHandler(raiser, "MyEvent", closure.Handler);
closure = null;
GC.Collect();
GC.Collect();
raiser.RaiseMyEvent();
Assert.AreEqual(false, didrun.Value);
}
迪德伦班
{
公共布尔值{get;set;}
}
类测试发布器
{
公共事件事件处理程序;
公共无效的RaiseMyEvent()
{
if(MyEvent!=null)
MyEvent(这个,EventArgs.Empty);
}
}
类TestClosure
{
public DidRun{get;set;}
公共事件处理程序{get;private set;}
公共测试关闭()
{
this.Handler=neweventhandler((s,e)=>didRun.Value=true);
}
}
[测试方法]
public void TestWeakReference()
{
var raiser=newtestEventPublisher();
var didrun=新的didrun();
var closure=newtestclosure{didRun=didRun};
WeakEventManager.AddHandler(raiser,“MyEvent”,closure.Handler);
闭包=空;
GC.Collect();
GC.Collect();
raiser.RaiseMyEvent();
aresequal(false,didrun.Value);
}
问题#2:有人能解释我为什么这次考试不及格吗
期望:这里我没有任何闭包(为了确保发生了什么,我取出了闭包),我只是有一个对象(闭包),它用WeakEventManager订阅一个事件,然后我删除了对它的引用(closure=null;)
我希望2个GC.Collect()调用能够清理我的旧闭包类,这样WeakEventManager就会删除订阅服务器,而不会运行处理程序,但测试失败。有什么想法吗
编辑:抱歉,通用参数不可见,现在它们是如果没有对lambda的引用,GC将收集围绕lambda创建的闭包,这是正确的 在单元测试中,您清空了
TestClosure
的本地实例,但是您将处理程序的硬引用传递给了WeakEventManager,而不是TestClosure
的实例。所以处理者继续生活
我相信这些例子说明了您在关闭时遇到的问题:
class DidRun
{
public bool Value { get; set; }
}
class TestEventPublisher
{
public event EventHandler<EventArgs> MyEvent;
public void RaiseMyEvent()
{
if (MyEvent != null)
MyEvent(this, EventArgs.Empty);
}
}
class TestClosure
{
static public EventHandler<EventArgs> Register(TestEventPublisher raiser, DidRun didrun)
{
EventHandler<EventArgs> handler = (s, e) => didrun.Value = true;
WeakEventManager<TestEventPublisher, EventArgs>.AddHandler(raiser, "MyEvent", handler);
return handler;
}
}
[TestMethod]
public void Test1()
{
var raiser = new TestEventPublisher();
var didrun = new DidRun();
TestClosure.Register(raiser, didrun);
// The reference to the closure 'handler' is not being held,
// it may or may not be GC'd (indeterminate result)
raiser.RaiseMyEvent();
Assert.IsTrue(didrun.Value);
}
[TestMethod]
public void Test2()
{
var raiser = new TestEventPublisher();
var didrun = new DidRun();
// The reference to the closure 'handler' is not being held, it's GC'd
TestClosure.Register(raiser, didrun);
GC.Collect();
GC.Collect();
raiser.RaiseMyEvent();
Assert.IsFalse(didrun.Value);
}
[TestMethod]
public void Test3()
{
var raiser = new TestEventPublisher();
var didrun = new DidRun();
// Keep local copy of handler to prevent it from being GC'd
var handler = TestClosure.Register(raiser, didrun);
GC.Collect();
GC.Collect();
raiser.RaiseMyEvent();
Assert.IsTrue(didrun.Value);
}
哇,非常感谢,我对此感到困惑,实际上我忽略了,传入的值是对处理程序的硬引用。现在我明白了。再次感谢你的帮助!!!这同样适用于本地方法,即它们也不能用作事件处理程序,原因基本相同。
// ConditionalWeakTable will hold the 'value' as long as the 'key' is not marked for GC
static private ConditionalWeakTable<INotifyPropertyChanged, EventHandler<PropertyChangedEventArgs>> _eventMapping =
new ConditionalWeakTable<INotifyPropertyChanged, EventHandler<PropertyChangedEventArgs>>();
public static void AddWeakPropertyChanged(this INotifyPropertyChanged item, Action<string> handlerAction)
{
EventHandler<PropertyChangedEventArgs> handler;
// Remove any existing handler for this item in case it's registered more than once
if (_eventMapping.TryGetValue(item, out handler))
{
_eventMapping.Remove(item);
PropertyChangedEventManager.RemoveHandler(item, handler, string.Empty);
}
handler = (s, e) => handlerAction(e.PropertyName);
// Save handler (closure) to prevent GC
_eventMapping.Add(item, handler);
PropertyChangedEventManager.AddHandler(item, handler, string.Empty);
}
class DidRun
{
static public string Value { get; private set; }
public void SetValue(string value) { Value = value; }
}
[TestMethod]
public void Test4()
{
var property = new ObservableObject<string>();
var didrun = new DidRun();
property.AddWeakPropertyChanged(
(x) =>
{
didrun.SetValue("Property Name = " + x);
});
GC.Collect();
GC.Collect();
property.Value = "Hello World";
Assert.IsTrue(DidRun.Value != null);
}