[英]Are Events in C# structs?
So I have a dictionary of EventHandlers, yet I find that when I attach to an event before adding the keyvaluepair to the dictionary, everything works fine. 所以我有一个EventHandlers的字典,但我发现当我在将keyvaluepair添加到字典之前附加到一个事件时,一切正常。 But if I add the keyvaluepair and then update the value of the eventhandler, the dictionary does not update. 但是,如果我添加keyvaluepair然后更新eventhandler的值,则字典不会更新。
public static event EventHandler TestEvent;
private static Dictionary<int, EventHandler> EventMapping = new Dictionary<int, EventHandler>();
//TestEvent += GTKWavePipeClient_TestEvent;
EventMapping.Add(0, TestEvent);
TestEvent += GTKWavePipeClient_TestEvent;
//test event is non null now. keyvaluepair in EventMapping has a value of null
Delegate types like EventHandler
are immutable types. 像EventHandler
这样的委托类型是不可变类型。 When you use assignment ( =
) or compound assignment ( +=
), a new instance is created. 使用赋值( =
)或复合赋值( +=
)时,将创建一个新实例。
The dictionary holds on to the old instance. 字典保留旧实例。
Delegate types are reference types, but the important thing here is their immutability. 委托类型是引用类型,但重要的是它们的不变性。
When you have an event
, the use of the +=
syntax is not even an assignment. 当你有一个event
,使用+=
语法甚至不是一个赋值。 It is an invocation of the add
accessor or of the event. 它是add
accessor或event的调用。 It will reassign the backing field (new instance) in a thread-safe way. 它将以线程安全的方式重新分配支持字段(新实例)。
Remember that you can author your event accessors yourself. 请记住,您可以自己编写事件访问者。 For example: 例如:
public static event EventHandler TestEvent
{
add
{
lock (lockObj)
{
EventHandler oldDel;
if (EventMapping.TryGetValue(0, out oldDel))
EventMapping[0] = oldDel + value;
else
EventMapping.Add(0, value);
}
}
remove
{
lock (lockObj)
{
EventHandler oldDel;
if (EventMapping.TryGetValue(0, out oldDel))
EventMapping[0] = oldDel - value;
}
}
}
private static readonly object lockObj = new object();
private static Dictionary<int, EventHandler> EventMapping = new Dictionary<int, EventHandler>();
With that code, when you go: 使用该代码,当你去:
TestEvent += GTKWavePipeClient_TestEvent;
your add
accessor is called with "implicit" parameter EventHandler value
set to GTKWavePipeClient_TestEvent
. 使用“隐式”参数EventHandler value
设置为GTKWavePipeClient_TestEvent
来调用您的add
访问GTKWavePipeClient_TestEvent
。
Delegates are immutable. 代表是不可改变的。 You are assigning a new object to TestEvent when invoking += to attach an event. 在调用+ =附加事件时,您正在为TestEvent分配新对象。 So in your non-working scenario, you have a different object within the Dictionary than the object which has the attached event. 因此,在非工作场景中,Dictionary中的对象与具有附加事件的对象不同。
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