WeakEventHandler.Fody

This is an add-in for Fody

Changes regular event handlers into weak event handlers by weaving a weak event adapter between source and subscriber. The subscriber is then no longer referenced by the event source, allowing it to be garbage collected. To understand the basic idea of a weak event adapter, see e.g. this Weak Events CodeProject article

Use this weaver if you have no control over the event source and can't change it into a weak event source.

NuGet installation

Install the WeakEventHandler.Fody NuGet package and update the Fody NuGet package:

PM> Install-Package WeakEventHandler.Fody
PM> Update-Package Fody

The Update-Package Fody is required since NuGet always defaults to the oldest, and most buggy, version of any dependency.

Your Code

public class EventSubscriber
{
    private readonly EventSource _source;

    public EventSubscriber(EventSource source)
    {
        _source = source;
    }

    public void Subscribe()
    {
        _source.AnyEvent += Source_AnyEvent;
    }

    public void Unsubscribe()
    {
        _source.AnyEvent -= Source_AnyEvent;
    }

    [WeakEventHandler.MakeWeak]
    private void Source_AnyEvent(object sender, EventArgs e)
    {
        // Do something
    }
}

What gets compiled

public class EventSubscriber
{
    private readonly EventSource _source;

    private readonly WeakEventAdapter<EventSource, EventSubscriber, EventArgs> EventSource_Source_AnyEvent_Adapter;

    public EventSubscriber(EventSource source)
    {
        EventSource_Source_AnyEvent_Adapter = new WeakEventAdapter<EventSource, EventSubscriber, EventArgs>(
            this, 
            Source_AnyEvent, 
            EventSource_Source_AnyEvent_Add, 
            EventSource_Source_AnyEvent_Remove);

        _source = source;
    }

    public void Subscribe()
    {
        EventSource_Source_AnyEvent_Adapter.Subscribe(_source);
    }

    public void Unsubscribe()
    {
        EventSource_Source_AnyEvent_Adapter.Unsubscribe(_source);
    }

    private void Source_AnyEvent(object sender, EventArgs e)
    {
        // Do something
    }

    private static void EventSource_Source_AnyEvent_Add(EventSource source, EventHandler<EventArgs> handler)
    {
        source.EventA += handler;
    }

    private static void EventSource_Source_AnyEvent_Remove(EventSource source, EventHandler<EventArgs> handler)
    {
        source.EventA -= handler;
    }

    ~EventSubscriber()
    {
        EventSource_Source_AnyEvent_Adapter.Release();
    }
}

This code is only schematic to make it readable, the real implementation is slightly different!