确保C#中的多播委托执行列表顺序? [英] Assuring multicast delegate execution list order in C#?
问题描述
经过阅读后,我了解到处理程序调用顺序与预订顺序相同,但不能保证.
所以可以说我有:
public event MYDEl ev;
和订户这样做:
ev+=GetPaper;
ev+=Print;
ev+=EjectPaper;
保存+确保执行列表顺序的最佳实践机制是什么?
What is the best practice mechanism of preserving +assuring the execution list order ?
推荐答案
If it's a field-like event, it will use simple delegate combination as per Delegate.Combine
, and that is guaranteed to preserve subscription order. From the docs for the return value:
具有调用列表的新委托,该调用列表按此顺序连接a和b的调用列表.
A new delegate with an invocation list that concatenates the invocation lists of a and b in that order.
一般而言对于事件,不能保证任何事情-这取决于实现.哎呀,它可能会忽略您进行的所有订阅.但实际上,任何理智的实现都会保留顺序.
In general for events, nothing is guaranteed - it's up to the implementation. Heck, it could ignore every subscription you ever make. In reality though, any sane implementation will preserve ordering.
一个恶作剧事件实现的示例:
Sample of a mischievous event implementation:
public class BadEventPublisher
{
public event EventHandler Evil
{
add { Console.WriteLine("Mwahahaha!"); }
remove { }
}
protected virtual void OnEvil(EventArgs e)
{
Console.WriteLine("Who cares? Subscriptions are ignored!");
}
}
这就像编写一个属性(例如)从getter返回一个随机数并忽略setter中的值一样.这更多的是理论上的问题,而不是实际的问题.
This is just like writing a property which (say) returns a random number from the getter and ignores the value in the setter. It's more of a theoretical problem than a real one.
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