Question

I have followed some tutorials on how to create custem event accessors. This is the code I have:

event ControlNameChangeHandler IProcessBlock.OnControlNameChanged
{
    add
    {
        lock (ControlNameChanged)
        {
            ControlNameChanged += value;
        }
    }
    remove
    {
        lock (ControlNameChanged)
        {
            ControlNameChanged -= value;
        }
    }
}

At the moment the code reaches lock(ControlNameChanged) in the add statament, nothing happens. The code doesn’t run any further. However my application is still working. It doesn’t freeze or something.

What goes wrong?

Answer 1

Somehow, someone else holds a lock. You shouldn’t use multicast delegate instances or events for locking, and you shouldn’t use public members either, because you cannot control who is locking and when.

Therefore I’d use a separate locking object like this:

private readonly object controlNameChangedSync = new object();

event ControlNameChangeHandler IProcessBlock.OnControlNameChanged
{
  add
  {
    lock (controlNameChangedSync)
    {
      ControlNameChanged += value;
    }
  }
  remove
  {
    lock (controlNameChangedSync)
    {
      ControlNameChanged -= value;
    }
  }
}

Note: the reference to the event changes when doing a += or -= on the delegate.