How to determine if an event is already subscribed

Question

In my .NET application I am subscribing to events from another class. The subscription is conditional. I am subscribing to events when the control is visible and de-subscrib

Answer 1

Can you put the decision making logic into the method that fires the event? Assuming you're using Winforms it'd look something like this:

 if (MyEvent != null && isCriteriaFulfilled)
{
    MyEvent();
}

Where isCriteriaFulfilled is determined by your visible/invisible logic.

// UPDATES /////

Further to your 1st comment would it not make sense to alter the behaviour inside your event handler depending on the value of this.Visible?

 a.Delegate += new Delegate(method1);
...
private void method1()
{
    if (this.Visible)
        // Do Stuff
}

Or if you really have to go with subscribing and unsubscribing:

 private Delegate _method1 = null;
...
if(this.visible) 
{
    if (_method1 == null)
        _method1 = new Delegate(method1);
    a.Delegate += _method1;
}
else if (_method1 != null)
{
    a.Delegate -= _method1;
}