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fix: ObserveCountChanged misses count if observer has side effect #121

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fix: ObserveCountChanged misses count if observer has side effect #121

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2 changes: 1 addition & 1 deletion src/ObservableCollections.R3/ObservableCollectionR3Extensions.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -438,10 +438,10 @@ protected override void Handler(in NotifyCollectionChangedEventArgs<T> eventArgs
case NotifyCollectionChangedAction.Add:
case NotifyCollectionChangedAction.Remove:
case NotifyCollectionChangedAction.Reset when countPrev != collection.Count:
countPrev = collection.Count;
observer.OnNext(collection.Count);
break;
}
countPrev = collection.Count;
}
}
}
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25 changes: 23 additions & 2 deletions tests/ObservableCollections.R3.Tests/ObservableCollectionExtensionsTest.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -161,7 +161,7 @@ public void ObserveReplace()
collection[1] = 444;
events.Count.Should().Be(1);
}

[Fact]
public void ObserveDictionaryReplace()
{
Expand Down Expand Up @@ -247,6 +247,27 @@ public void ObserveCountChanged()
events.Count.Should().Be(3);
}

[Fact]
public void ObserveCountChanged_WithSideEffect()
{
var events = new List<int>();
var collection = new ObservableList<int>([]);

using var _ = collection.ObserveCountChanged().Subscribe(count =>
{
events.Add(count);
// Side effect - when count is 1, clear the list
if(count == 1) collection.Clear();
});

events.Should().BeEmpty();

collection.Add(12);

collection.Count.Should().Be(0);
events.Should().BeEquivalentTo([1, 0]);
}

[Fact]
public void ObserveCountChanged_NotifyCurrent()
{
Expand All @@ -257,4 +278,4 @@ public void ObserveCountChanged_NotifyCurrent()
.Subscribe(count => events.Add(count));
events[0].Should().Be(3);
}
}
}