Prism - EventAggregator.GetEvent<> .Subscribe（） - 使用泛型&约束上

问题描述

如果我使用诸如

的某些东西b
$ b

  eventAggregator.GetEvent< string>（）。订阅（MyMethod）
  

然后它一切正常，当事件被发布时，我的方法被触发。

然而，当移动到更复杂除了I字符串以外的对象我遇到了问题。

我有一堆类都来自接口（IRequest），例如

我有我的事件类设置如下

  public class MyEvent< TRequest> ：PubSubEvent< MyClass< TRequest>> TRequest：IRequest {} 
  

我有一个泛型类（MyClass），它使用IRequest的对象现在，让我说我发布了一个MyClass的事件，它使用了它内部的对象Profile：

  eventAggregator.GetEvent< MyEvent< Profile>>（）。Publish（myProfileObject）; 
  

在我的订阅中，我想要一个可以捕获MyEvent的所有事件的方法 - 不管T是否为配置文件或从IRequest派生的其他对象 - 这是我似乎有问题的地方。

在下面的例子中，第一个作品，但第二个没有 - 我最好喜欢使用与第二种类似的东西。

  eventAggregator.GetEvent< MyEvent< Profile>>（）。订阅（TEST1）; 
 void test1（MyClass< Profile> obj）
 {
 // Some some here 
} 
 
 eventAggregator.GetEvent< MyEvent< IRequest>> （）.Subscribe（TEST2）; 
 void test2< T>（MyClass< T> obj）其中T：IRequest 
 {
 //永远不会被调用
} 
  

我的假设是，因为配置文件派生自IRequest，那么它应该工作？但它不!! !!

任何帮助将不胜感激。

更新

如果我使用以下内容，它确实有效，但需要我为每种可用的IRequest创建一个单独的订阅 - 我只希望只有一个订阅。

  eventAggregator.GetEvent< MyEvent< Profile>>（）。Subscribe（test2）; 
 eventAggregator.GetEvent< MyEvent< User>>（）。Subscribe（test2）; 
  

解决方案

MyEvent< IRequest> 和 MyEvent< Profile> 不一样，所以EventAggregator不会将此视为同一事件。为了允许协变类型，你可以在C＃4中使用 out 修饰符来解决它。像这样的东西应该可以工作：

  public interface IMyClass< out T>其中T：IRequest {} 
 
 public class MyClass< T> ：IMyClass< T>其中T：IRequest {} 
 
 public class MyEvent< TValue> ：PubSubEvent< IMyClass< TValue>> TValue：IRequest {} 
  

然后你的事件聚合器看起来像这样：

  _eventAggregator.GetEvent< MyEvent< IRequest>>（）。Subscribe（Received）; 
 
 private void Received（IMyClass< IRequest> obj）
 {
 
} 
 
 _eventAggregator.GetEvent< MyEvent< IRequest>> （）.Publish（new MyClass< Profile>（））; 
  

这有帮助吗？

I am having an issue subscribing to events with the event Aggregator that comes as part of the prism framework.

If I use something such as

eventAggregator.GetEvent<string>().Subscribe(MyMethod)

then it all works ok, my method fires when an event has been published.

However, when moving to a more complex object other than I string I run into problems.

I have a bunch of classes that all derive from an Interface (IRequest) for example

I have my event class setup as follows

public class MyEvent<TRequest> : PubSubEvent<MyClass<TRequest>> where TRequest : IRequest {}

I have a generic class (MyClass) that uses an object of IRequest inside it - again, all seems to work ok at this point.

Now, lets say I publish an event of MyClass that uses the object Profile inside it:

eventAggregator.GetEvent<MyEvent<Profile>>().Publish(myProfileObject);

In my subscription I would like a method that can catch all events of MyEvent - Irrelevant of whether T is Profile or some other object that derives from IRequest - this is where I seem to be having problems.

In the following examples, the first works, but the second doesn't - I would ideally like to use something similar to the second.

eventAggregator.GetEvent<MyEvent<Profile>>().Subscribe(test1);
void test1 (MyClass<Profile> obj)
{
  //Some stuff here
}

eventAggregator.GetEvent<MyEvent<IRequest>>().Subscribe(test2);
void test2<T>(MyClass<T> obj) where T : IRequest
{
  //never gets called
}

My assumption is that because Profile derives from IRequest then it should work??? But it doesn't!!

Any help would be appreciated.

UPDATE
If I use the following, it does work, but would require me to create a separate subscription for each type of IRequest available - I'm looking to only have the one subscription.

eventAggregator.GetEvent<MyEvent<Profile>>().Subscribe(test2);
eventAggregator.GetEvent<MyEvent<User>>().Subscribe(test2);

解决方案

MyEvent<IRequest> and MyEvent<Profile> are not the same, so the EventAggregator doesn't see this as the same event. To allow for covariant types, you can fix it with the out modifier in C# 4. Something like this should work:

public interface IMyClass<out T> where T : IRequest { }

public class MyClass<T> : IMyClass<T> where T : IRequest { }

public class MyEvent<TValue> : PubSubEvent<IMyClass<TValue>> where TValue : IRequest { }

Then your event aggregator would look something like:

 _eventAggregator.GetEvent<MyEvent<IRequest>>().Subscribe(Received);

 private void Received(IMyClass<IRequest> obj)
 {

 }

_eventAggregator.GetEvent<MyEvent<IRequest>>().Publish(new MyClass<Profile>());

Does this help?

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