如何引用C＃中的事件 [英] How to reference an event in C#

问题描述

我有以下类，它有一个公共事件叫做 LengthChanged ：

I have the following class, which has one public event called LengthChanged:

class Dimension
{
    public int Length
    {
        get
        {
            return this.length;
        }
        set
        {
            if (this.length != value)
            {
                this.length = value;
                this.OnLengthChanged ();
            }
    }

    protected virtual void OnLengthChanged()
    {
        var handler = this.LengthChanged;
        if (handler != null)
        {
            handler (this, System.EventArgs.Empty);
        }
    }

    public event System.EventHandler LengthChanged;

    private int length;
}

我想能够注册/注销这个事件的处理程序方法称为 Observer ，它们不了解 Dimension 类的任何内容。我想出了两个场景，其中没有一个是非常令人满意的：

I would like to be able to register/unregister handlers for this event in a method called Observer, which does not know anything about the Dimension class. I have come up with two scenarios, none of which are really satisfying:

1. 定义界面 ILengthChanged 与 LengthChanged 事件，然后确保维度实现 ILengthChanged 。那么我必须为我定义的每个接口提供 Observer 方法的一个实现。这绝对不够通用。我真的希望能够简单地传递一个 System.EventHandler 事件的引用。

1. Define an interface ILengthChanged with the LengthChanged event, then make sure Dimension implements ILengthChanged. Then I have to provide one implementation of the Observer method for every interface I define. This by no way generic enough. I'd really want to be able to simply pass in a reference to a System.EventHandler event.

使用 System.Action< System.EventHandler> 回调注册和注销 Observer 方法中的事件处理程序，就像这样：

Use System.Action<System.EventHandler> callbacks for registering and unregistering the event handler in the Observer method, just like that:

class Foo
{
public void Observer（System.Action register，
System.Action unregister）
{
注册（this.MyEventHandler）;

class Foo { public void Observer(System.Action register, System.Action unregister) { register (this.MyEventHandler);

    // keep track of the unregister callback, so that we can unregister
    // our event handler later on, if needed...
}

private void MyEventHandler(object sender, System.EventArgs e)
{
    ...
}

}

然后将这样调用：

Foo foo = ...;
Dimension dim = ...;

foo.Observer (x => dim.LengthChanged += x, x => dim.LengthChanged -= x);

当执行时，确实会最终连接 LengthChanged 事件与内部事件处理程序 MyEventHandler 。但这不是很优雅。我会喜欢能够写这个：

and which, when executed, will indeed end up wiring the LengthChanged event with the internal event handler MyEventHandler. But this is not very elegant. I would have loved to be able to write this instead:

Foo foo = ...;
Dimension dim = ...;

foo.Observer (dim.LengthChanged);

但我不知道如何实现。也许我错过了一些非常明显的东西？我想，一些动态魔术可以做这个伎俩，不知何故，但这不会执行编译时类型检查：我不希望 Observer 传递对不满足 System.EventHandler 事件签名的事件的引用。

but I've no idea how this could be achieved. Maybe I am missing something really obvious here? I guess that some dynamic magic could do the trick, somehow, but this would not enforce compile-time type checking: I don't want the users of Observer to pass in references to events which do not satisfy the System.EventHandler event signature.

推荐答案

不幸的是，没有一个这样做的方法。事件一般不是.NET的一流公民 - 尽管F＃试图在那里推广它们。

Unfortunately there isn't really a way of doing this. Events aren't first class citizens in .NET in general - although F# tries to promote them there.

传递订阅/取消订阅委托或使用指示活动名称（后者通常较短，但在编译时显然较不安全）。

Either pass in the subscribe/unsubscribe delegate or using a string indicating the name of the event. (The latter is often shorter, but obviously less safe at compile-time.)

这些是反向扩展需要 - 如果有一个更干净的方法，我确定他们会使用它：（

Those are the approaches which Reactive Extensions takes - if there were a cleaner way of doing it, I'm sure they would be using that :(

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