如何取消注册我的Lambda回调？

Question

如果我创建一个lambda回调,如下所示:

var someInstance = new SomeObject();

someInstance.Finished += (obj, args) =>
{
      // Do something

      // Deregister here
};

someInstance.DoAction();

我如何取消注册回调作为实际处理程序代码的一部分？这种模式是理想的,因为我可以确保它尽快释放.

我见过类似的问题但不是直接解决这类例子的问题.

Answer 1

有点像,

var someInstance = new SomeObject();

EventHandler myDelegate = null;
myDelegate = (obj, args) =>
{
      // Do something

      // Deregister here
      someInstance.Finished -= myDelegate;
};
someInstance.Finished += myDelegate;

someInstance.DoAction();

Answer 2

如果您想要取消注册,那么最好将lambda定义为Action,以便您可以编写:

someInstance.Finished += MyCustomAction;

然后

someInstance.Finished -= MyCustomAction;

Answer 3

您可以MethodInfo.GetCurrentMethod在lambda中使用以检索lambda的MethodInfo.

使用MethodInfo,您可以使用Delegate.CreateDelegate获取代表lambda的正确类型的委托.

使用委托,您可以取消注册lambda,而无需将函数存储在变量中或使其成为命名方法.

class MyClass 
{
    public event EventHandler TheEvent;

    void TestIt()
    {
        TheEvent += (sender, eventargs) => 
            {
            Console.WriteLine("Handled!"); // do something in the handler

            // get a delegate representing this anonymous function we are in
            var fn = (EventHandler)Delegate.CreateDelegate(
                             typeof(EventHandler), sender, 
                             (MethodInfo)MethodInfo.GetCurrentMethod());

            // unregister this lambda when it is run
            TheEvent -= fn;
        };


        // first time around this will output a line to the console
        TheEvent(this, EventArgs.Empty);

        // second time around there are no handlers attached and it will throw a NullReferenceException
        TheEvent(this, EventArgs.Empty);
    }

}