如何在一行中安全取消订阅动作？

Question

I would like to know if I can unsubscribe from a C# Action in a safe way in just one line of code instead of having to write this:

if(publisher.RaiseCustomEvent != null)
{
    publisher.RaiseCustomEvent -= HandleCustomEvent; 
}

A simple example:

public class Publisher
{
    public Action RaiseCustomEvent;

    public MyClass() { }
}

public class Subscriber
{
    Publisher _publisher;
    public Subscriber()
    {
        _publisher = new Publisher();
        _publisher.RaiseCustomEvent += HandleCustomEvent;
    }

    // ...

    public void Dispose()
    {
        // DO this safely in one line
        if(_publisher.RaiseCustomEvent != null)
        {
            _publisher.RaiseCustomEvent -= HandleCustomEvent; 
        }
    }
}

Answer 1

if I can unsubscribe from a C# Action in a safe way in just one line of code

Yes, you don't even need the null check:

//if(publisher.RaiseCustomEvent != null)
{
    publisher.RaiseCustomEvent -= HandleCustomEvent; 
}

and then you can clean that up of course.
This is null-safe, probably not thread-safe.

Since an event starts out as null you have to be able to subscribe with += on a null delegate. The same holds for unsubscribing.

I don't even think it matters whether RaiseCustomEvent is an event or an Action field. But please be clear about that.

You do of course have to make sure that you raise the event in a null-safe way, either with if ( ... != null) or with a ?.Invoke() .

---

Now that you have posted the code, your RaiseCustomEvent is a public field. That has some drawbacks with regard to encapsulation. Using an event is the common practice:

public class Publisher
{
    //public Action RaiseCustomEvent;      
    public event Action RaiseCustomEvent;              
}

This will only allow += and -= , and prevents overwriting with RaiseCustomEvent = MySingleMethod