How to ensure an event is only subscribed to once

Question

I would like to ensure that I only subscribe once in a particular class for an event on an instance.

For example I would like to be able to do the following:

Answer 1

I did this recently and I'll just drop it here so it stays:

private bool subscribed;

if(!subscribed)
{
    myClass.MyEvent += MyHandler;
    subscribed = true;
} 

private void MyHandler()
{
    // Do stuff
    myClass.MyEvent -= MyHandler;
    subscribed = false;
}