When to use callbacks instead of events in c#?

Question

Forgive me if this a stupid question, I admit I haven\'t thought about it much.

But when would you favour using a callback (i.e, passing in a Func or Action), as oppo

Answer 1

Generally, I use a callback if it is required, whereas an event is used when it should be optional. Don't expose an event if you're expecting there to always be something listening.

Consider the following:

public class MyClass_Event
{
    public event EventHandler MakeMeDoWork;

    public void DoWork()
    {
        if (MakeMeDoWork == null)
            throw new Exception("Set the event MakeMeDoWork before calling this method.");
        MakeMeDoWork(this, EventArgs.Empty);
    }
}

versus:

public class MyClass_Callback
{
    public void DoWork(EventHandler callback)
    {
        if (callback == null)
            throw new ArgumentException("Set the callback.", "callback"); // better design
        callback(this, EventArgs.Empty);
    }
}

The code is almost the same as the callback can be passed as null, but at least the exception thrown can be more relevant.