Note that delegates don't keep the publisher alive (they only keep the target=subscriber alive), so no number of subscriptions will (by themselves) keep the broadcaster alive. As such, from this perspective it doesn't matter whether it is disposed or not. When there are no items referencing the broadcaster (and the event-subscriptions don't matter for this), it will be eligible for collection.
Essentially, a delegate is a (list of) pair(s) of MethodInfo and object references; the method to call, and the object to invoke as "arg0" (aka this). It simply doesn't have a reference to the object raising the event.
Here's evidence that a listener does not keep the source alive; you should see that "Source 1" gets collected, even though we still have the matching listener that is subscribed. As expected, "Listener 2" does not get collected, since we still have the matching broadcaster:
class DataSource
{
public DataSource(string name) { this.name = name; }
private readonly string name;
~DataSource() { Console.WriteLine("Collected: " + name); }
public event EventHandler SomeEvent;
}
class DataListener
{
public DataListener(string name) { this.name = name; }
private readonly string name;
~DataListener() { Console.WriteLine("Collected: " + name); }
public void Subscribe(DataSource source)
{
source.SomeEvent += SomeMethodOnThisObject;
}
private void SomeMethodOnThisObject(object sender, EventArgs args) { }
}
static class Program
{
static void Main()
{
DataSource source1 = new DataSource("Source 1"),
source2 = new DataSource("Source 2");
DataListener listener1 = new DataListener("Listener 1"),
listener2 = new DataListener("Listener 2");
listener1.Subscribe(source1);
listener2.Subscribe(source2);
// now we'll release one source and one listener, and force a collect
source1 = null;
listener2 = null;
GC.Collect(GC.MaxGeneration, GCCollectionMode.Forced);
GC.WaitForPendingFinalizers(); // source 1 gets collected, ONLY
Console.WriteLine("Done");
Console.ReadLine();
GC.KeepAlive(source2); // prevents collection due to optimisation
GC.KeepAlive(listener1); // prevents collection due to optimisation
}
}