From 45207dd7c681bb0f01ea1a91cbcfe0cd0592ecd7 Mon Sep 17 00:00:00 2001
From: Steven Kirk <grokys@gmail.com>
Date: Fri, 4 Mar 2016 01:58:41 +0100
Subject: [PATCH] Make ExpressionObserver complete...

When rootObservable or _update completes.
---
 .../Perspex.Markup/Data/ExpressionObserver.cs | 20 ++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/src/Markup/Perspex.Markup/Data/ExpressionObserver.cs b/src/Markup/Perspex.Markup/Data/ExpressionObserver.cs
index 52e619872f..cebf0daebd 100644
--- a/src/Markup/Perspex.Markup/Data/ExpressionObserver.cs
+++ b/src/Markup/Perspex.Markup/Data/ExpressionObserver.cs
@@ -193,7 +193,18 @@ namespace Perspex.Markup.Data
 
             if (_node != null)
             {
-                var subscription = _node.Subscribe(observer);
+                IObservable<object> source = _node;
+
+                if (_rootObservable != null)
+                {
+                    source = source.TakeUntil(Complete(_rootObservable));
+                }
+                else if (_update != null)
+                {
+                    source = source.TakeUntil(Complete(_update));
+                }
+
+                var subscription = source.Subscribe(observer);
 
                 return Disposable.Create(() =>
                 {
@@ -221,6 +232,13 @@ namespace Perspex.Markup.Data
             }
         }
 
+        private static IObservable<Unit> Complete<T>(IObservable<T> input)
+        {
+            return Observable.Merge(
+                input.TakeLast(1).Select(_ => Unit.Default),
+                input.IsEmpty().Where(x => x).Select(_ => Unit.Default));
+        }
+
         private void IncrementCount()
         {
             if (_count++ == 0 && _node != null)