MvvmCross Messenger Plugin Purging subscriptions

Question

I'm using the Messenger Plugin in my MvvmCross application and have noticed that it sometimes purges my subscriptions ("One or more listeners failed - purge scheduled"). This is causing an error in my application. By default I am using the weak reference for the subscriptions and I am not unsubscribing from the message.

Do I need to be Unsubscribing? Isn't the point of a weak reference to allow it to be garbage collected?

My BaseView is subscribing in the constructor as shown below.

 public BaseView()
    {
        _messenger = Mvx.Resolve<IMvxMessenger>();
        _messenger.Subscribe<MyMessage>(s => Method());
    }

Below is my Broadcast Receiver publishing my message.

 var _messenger = Mvx.Resolve<IMvxMessenger>();
 _messenger.Publish<MyMessage>(new MyMessage(this));

I have an idea of trying to unsubscribe in the onDestroy.

If you could give me some insight as to why this is happening and a possible resolution I would be grateful.

Thanks in advance.

This question would benefit from some code instead of "My BaseView is subscribing in the constructor and have an idea of trying to unsubscribe in the onDestroy." — Stuart
I've added some code, let me know if you need any more information. — Jake

Stuart Stuart · Accepted Answer · 2013-10-29T14:51:58

When using weak references, it's important to store the returned subscription token in a class-level field.

private IDisposable _token;

public BaseView()
{
    _messenger = Mvx.Resolve<IMvxMessenger>();
    _token = _messenger.Subscribe<MyMessage>(OnMyMessage);
}

private void OnMyMessage(MyMessage msg)
{
   // code
}

If you don't do this, then the GarbageCollector is free to collect the subscription.

For more on this, please see the section on "This GC-based unsubscription will occur whenever the subscription token returned from Subscribe is Garbage Collected" in the wiki - https://github.com/MvvmCross/MvvmCross/wiki/MvvmCross-plugins#messenger

MvvmCross Messenger Plugin Purging subscriptions

1 Answers