我一直在思考,在适当的情况下,是否值得使用类似以下内容(粗略概念代码)来实现弱事件:
class Foo {
private WeakEvent<EventArgs> _explodedEvent = new WeakEvent<EventArgs>();
public event WeakEvent<EventArgs>.EventHandler Exploded {
add { _explodedEvent += value; }
remove { _explodedEvent -= value; }
}
private void OnExploded() {
_explodedEvent.Invoke(this, EventArgs.Empty);
}
public void Explode() {
OnExploded();
}
}
使用更传统的C#语法允许其他类对事件进行订阅和取消订阅,而在内部实际上是通过弱引用来实现:
static void Main(string[] args) {
var foo = new Foo();
foo.Exploded += (sender, e) => Console.WriteLine("Exploded!");
foo.Explode();
foo.Explode();
foo.Explode();
Console.ReadKey();
}
WeakEvent<TEventArgs>
帮助类定义如下:
public class WeakEvent<TEventArgs> where TEventArgs : EventArgs {
public delegate void EventHandler(object sender, TEventArgs e);
private List<WeakReference> _handlers = new List<WeakReference>();
public void Invoke(object sender, TEventArgs e) {
foreach (var handler in _handlers)
((EventHandler)handler.Target).Invoke(sender, e);
}
public static WeakEvent<TEventArgs> operator + (WeakEvent<TEventArgs> e, EventHandler handler) {
e._handlers.Add(new WeakReference(handler));
return e;
}
public static WeakEvent<TEventArgs> operator - (WeakEvent<TEventArgs> e, EventHandler handler) {
e._handlers.RemoveAll(x => (EventHandler)x.Target == handler);
return e;
}
}
这是一个好的方法吗?这种方法有什么不良副作用吗?