UnHooking Events with Lambdas in C#

问题:

I often run into a situation where I want to subscribe to an event, but I want to use a lambda to do so:

public class Observable
{
    public event EventHandler SomethingHappened;

    public void DoSomething()
    {
        // Do Something...
        OnSomethingHappened();
    }
}

// Somewhere else, I hook the event
observable.SomethingHappened += (sender, args) => Console.WriteLine("Something Happened");

The problem I run into is that I don't know how to unhook the event. Since the lambda creates an anonymous delegate under the hood, I have nothing to call -= on.

Now, I could just create a method:

private void SomethingHappened(object sender, EventArgs args)
{
    Console.WriteLine("Something Happened");
}

And then I can hook/unhook all I want:

observable.SomethingHappened += SomethingHappened;
observable.SomethingHappened -= SomethingHappened;

But I'd really, really, really like to use my lambda instead. In a more complicated example, lambdas come in really handy here.

I am pretty sure that I am out of luck... but I was wondering if anyone out there has figured out a way to do this?

回答1:

Unforutantely there is not a great way to do this. You are really stuck with one of two options

• Use a method as you described
• Assign the lambda to a variable and use the variable to add / remove the event

回答2:

This question was already asked

• How to unsubscribe from an event which uses a lambda expression?
• Unsubscribe anonymous method in C#

The answer is: put your lambda in a variable.

EventHandler handler = (sender, args) => Console.WriteLine("Something Happened");
observable.SomethingHappened +=  handler;
observable.SomethingHappened -=  handler;

回答3:

Well, if you know your code is the only one hooking up the event, assigning null to the event variables will remove all delegates (but can be very bad form if you want the code to be extensible).

Otherwise, you should just keep the lambda around in a separate variable and use that to unhook the event.