C＃：初始化事件处理程序与虚拟 [英] C#: Initializing an event handler with a dummy

问题描述

我见过这种代码一些地方：

I've seen this sort of code some places:

public event SomeEventHandler SomeEvent = (s, e) => { };

是一个做事的推荐的方式？这是什么解决的，它有任何值得注意的副作用吗？请问我还要做null检查？或者是，正是我不必做任何更多？ ？将垃圾收集还是因为它应该工作

Is that a recommended way of doing things? What does it solve, and does it have any noteworthy side effects? Will I still have to do null checks? Or is that exactly what I don't have to do any more? Will garbage collection still work as it should?

---

例如：

private PropertyChangedEventHandler propertyChanged;
private readonly object propertyChangedLock = new object();
public event PropertyChangedEventHandler PropertyChanged
{
    add
    {
        lock (propertyChangedLock)
            propertyChanged += value;
    }
    remove
    {
        lock (propertyChanged)
            propertyChanged -= value;
    }
}
protected void OnPropertyChanged(string propertyName)
{
    PropertyChangedEventHandler handler;
    lock (propertyChangedLock)
        handler = propertyChanged;

    if (handler != null)
        handler(this, new PropertyChangedEventArgs(propertyName));
}

我能改第一行成这样：

Could I change the first line into this:

private PropertyChangedEventHandler propertyChanged = (s, e) => { };

然后跳过OnPropertyChanged方法空检查？如果我再跳过空支票可能我随后也跳了锁？如果是这样，会给我这样的：

And then skip the null-check in the OnPropertyChanged method? And if I then skip the null-check could I then also skip the lock? If so that would give me this:

protected void OnPropertyChanged(string propertyName)
{
    propertyChanged(this, new PropertyChangedEventArgs(propertyName));
}

请问服用初始化到时是安全的？还是有一些副作用，我错过了什么？

Would that be safe when taking the initialization into account? Or are there some side effects I have missed?

推荐答案

尽管你不需要做无效的检查，如果你真的要尽量使事件线程安全的，你还需要将其锁获取：

While you don't need to do the nullity checks, if you really want to try to make the event thread-safe, you still need to fetch it in a lock:

protected void OnPropertyChanged(string propertyName)
{
    PropertyChangedEventHandler handler;
    lock (propertyChangedLock)
    {
        handler = propertyChanged;
    }
    handler(this, new PropertyChangedEventArgs(propertyName));
}

否则，你可能没有获取最新的价值 - 如果事件处理程序正在在不同的线程增加，理论上可以引发事件永远永远不会调用新的处理程序。在实践中，我相信你会几乎总是跑不掉而不锁，但在内存模型项你应该有部分的排序围栏。

我个人建议你不要的尝试的使事件线程安全的。

Personally I recommend that you don't try to make the events thread-safe.

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