Concurrent ObservableCollection in Portable Class Library

Question

I have a solution with Xamarin Android, Xamarin iOS and WPF projects.

There is a lot of multithreading activity mainly in the ViewModels and data access components, we use INotifyDataErrorInfo in our model and of course XAML DataBinding with ObservableCollection lists.

What I need is an ObservableCollection implementation for all the platforms that will make the list concurrent to make sure that only one thread can modify the collection.

In my research I found couple of implementations with this one the closest to what I want, but uses Thread and reflection that are not available in a Portable Class Library. http://pastebin.com/hKQi6EHD . I guess modifying and abs

Any sources available to get me to the right track?

Answer 1

I stumbled on this same issue when working on a similar problem. I can up with 2 possible solutions, 1 use a concurrent collection for your repository and a facade to update the observable collection. 2 create your own ConcurrentObservable collection. 2 is risky because you need to get the sync correct or it will affect performance. My thoughts are you could just wrap the ConcurrentCollection and then implement INotifyPropertyChanged. I would think a hash or some type of efficient comparison should be done before raising the event. You could also make your own INotifyPropertyChangedAsync event. Just my thoughts.

Adapter:

ConcurrentQueue _concurrentQueue = new ConcurrentQueue<object>();

Add(object o)
{
     _concurrentQueue.Enqueue(o);
     if (!_updateStatus)
        {
            Task.Run(() => UpdateBindingCollection()).ConfigureAwait(true); 
        }
}

On enter of the UpdateBindingCollection _updateStatus = true signaling that we already have an update in the works.

void UpdateBindingCollection()
    {
        while (_concurrentQueue.Count > 0)
        {
            object o;
            _concurrentQueue.Dequeue(out o);
            _observableCollection.Add(o);
        }
    }

Easier but blocking:

Lock(_observableCollection)
{
       //Perform update either with add or range. 
}