[Core] Fix internal children clear logic (#820)

* Fix InternalChildren clear logic

* Improve InternalChildren clear logic

* Add test code to verify InternalChildren clear logic

* Add missing test cases

* Improve time complexity of clear logic

* Fix the test case where InvalidOperationException occurs.

* Correct the name casing of the test case

* Modify a wrong test code

1 files changed, 4 insertions, 4 deletions

diff --git a/Xamarin.Forms.Core/TemplateUtilities.cs b/Xamarin.Forms.Core/TemplateUtilities.cs
index 4a8d21b9..e78f4836 100644
--- a/Xamarin.Forms.Core/TemplateUtilities.cs
+++ b/Xamarin.Forms.Core/TemplateUtilities.cs
@@ -58,9 +58,9 @@ namespace Xamarin.Forms
 			var newElement = (Element)newValue;
 			if (self.ControlTemplate == null)
 			{
-				for (var i = 0; i < self.InternalChildren.Count; i++)
+				while (self.InternalChildren.Count > 0)
 				{
-					self.InternalChildren.Remove(self.InternalChildren[i]);
+					self.InternalChildren.RemoveAt(self.InternalChildren.Count - 1);
 				}
 
 				if (newValue != null)
@@ -104,9 +104,9 @@ namespace Xamarin.Forms
 			}
 
 			// Now remove all remnants of any other children just to be sure
-			for (var i = 0; i < self.InternalChildren.Count; i++)
+			while (self.InternalChildren.Count > 0)
 			{
-				self.InternalChildren.Remove(self.InternalChildren[i]);
+				self.InternalChildren.RemoveAt(self.InternalChildren.Count - 1);
 			}
 
 			ControlTemplate template = self.ControlTemplate;