RX PropertyChanged GroupBy deadlock - system.reactive

Question

I am trying to use Reactive Extensions to throttle PropertyChanged notifications. There are examples of doing this using GroupBy, but with one Subscription created for each PropertyName.
I want to handle the PropertyChanged event for all properties, and I need to Throttle those events for each PropertyName.
This is what I have so far, but it causes a deadlock.
ValuesPropertyChanged = Observable.FromEventPattern<PropertyChangedEventArgs>(value, "PropertyChanged")
.GroupBy(o => o.EventArgs.PropertyName)
.First()
.Throttle(TimeSpan.FromSeconds(2))
.Subscribe(args => HandlePropertyChanged(args.EventArgs.PropertyName));
The deadlock happens in the call to .First().
It still locks if I change that line to:
.Select(o => o.First())
I have also tried
.Select(o => o.FirstAsync())
The examples for GroupBy here look pretty concise, but I am incapable of wrapping my head around converting these examples to my solution.
Why does this cause a deadlock, and what should I do to make this work?

Answer 1

I think this might be what you're after:
// assume MyObj : INotifyPropertyChanged, naturally
var value = new MyObj();
Action<string> HandlePropertyChanged =
name => Console.WriteLine("Got a change for name:" + name);
// The query
var valuesPropertyChanged =
// create from event stream
from propChange in Observable.FromEventPattern<PropertyChangedEventArgs>(
value,
"PropertyChanged")
// group events by property name
group propChange by propChange.EventArgs.PropertyName into batchByName
// Throttle the resulting batch
from throttledByName in batchByName.Throttle(TimeSpan.FromSeconds(1))
// then select each item of the "throttled output"
select throttledByName;
valuesPropertyChanged.Subscribe(args =>
HandlePropertyChanged(args.EventArgs.PropertyName));
for(int i=0;i<10;i++)
{
value.Value1 = i.ToString();
value.Value2 = (i-1).ToString();
}
Output:
Got a change for name:Value2
Got a change for name:Value1
Here is the same but with extension methods:
var valuesPropertyChanged =
Observable.FromEventPattern<PropertyChangedEventArgs>(
_vm,
"PropertyChanged")
.GroupBy(propchange => propchange.EventArgs.PropertyName)
.Select(o => o.Throttle(TimeSpan.FromSeconds(1)))
.Merge();