From 2477868b290961fba88d4cc49616a94343331ada Mon Sep 17 00:00:00 2001
From: "Dr.Rx" <david.rey@nventive.com>
Date: Sun, 26 May 2019 10:13:18 -0400
Subject: [PATCH] Improve perfe by batching collection change updates

---
 .../CalculatorObservableCollection.cs         | 32 ++++++++++++++++++-
 .../ViewModels/UnitConverterViewModel.cs      | 32 +++++++++++--------
 2 files changed, 50 insertions(+), 14 deletions(-)

diff --git a/src/Calculator.Shared/CalcManager/CalculatorObservableCollection.cs b/src/Calculator.Shared/CalcManager/CalculatorObservableCollection.cs
index 0e02de9a..f7394847 100644
--- a/src/Calculator.Shared/CalcManager/CalculatorObservableCollection.cs
+++ b/src/Calculator.Shared/CalcManager/CalculatorObservableCollection.cs
@@ -1,11 +1,41 @@
 using System;
 using System.Collections.ObjectModel;
+using System.Collections.Specialized;
 using System.Linq;
 
 namespace CalculatorApp
 {
 	public class CalculatorObservableCollection<TType> : ObservableCollection<TType>
 	{
+		private int _batchUpdateCount;
+
+		public IDisposable BatchUpdate()
+		{
+			++_batchUpdateCount;
+
+			return Uno.Disposables.Disposable.Create(Release);
+
+			void Release()
+			{
+				if (--_batchUpdateCount <= 0)
+				{
+					OnCollectionChanged(new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset));
+				}
+			}
+		}
+
+
+		/// <inheritdoc />
+		protected override void OnCollectionChanged(NotifyCollectionChangedEventArgs e)
+		{
+			if (_batchUpdateCount > 0)
+			{
+				return;
+			}
+
+			base.OnCollectionChanged(e);
+		}
+
 		public void Append(TType item)
 		{
 			Add(item);
@@ -16,4 +46,4 @@ namespace CalculatorApp
 			return this[index];
 		}
 	}
-}
\ No newline at end of file
+}
diff --git a/src/Calculator.Shared/ViewModels/UnitConverterViewModel.cs b/src/Calculator.Shared/ViewModels/UnitConverterViewModel.cs
index 19a40527..4af46e11 100644
--- a/src/Calculator.Shared/ViewModels/UnitConverterViewModel.cs
+++ b/src/Calculator.Shared/ViewModels/UnitConverterViewModel.cs
@@ -950,18 +950,21 @@ namespace CalculatorApp.ViewModel
 
 		void BuildUnitList(CalculatorList<UCM.Unit> modelUnitList)
 		{
-			m_Units.Clear();
-			foreach (UCM.Unit modelUnit in modelUnitList)
+			using (m_Units.BatchUpdate())
 			{
-				if (!modelUnit.isWhimsical)
+				m_Units.Clear();
+				foreach (UCM.Unit modelUnit in modelUnitList)
 				{
-					m_Units.Append(new Unit(modelUnit));
+					if (!modelUnit.isWhimsical)
+					{
+						m_Units.Append(new Unit(modelUnit));
+					}
 				}
-			}
 
-			if (m_Units.Count == 0)
-			{
-				m_Units.Append(EMPTY_UNIT);
+				if (m_Units.Count == 0)
+				{
+					m_Units.Append(EMPTY_UNIT);
+				}
 			}
 		}
 
@@ -1284,11 +1287,14 @@ namespace CalculatorApp.ViewModel
 
 		void InitializeView()
 		{
-			CalculatorList<UCM.Category> categories = m_model.GetCategories();
-			for (uint i = 0; i < categories.Size(); i++)
+			using (m_Categories.BatchUpdate())
 			{
-				Category category = new Category(categories[i]);
-				m_Categories.Append(category);
+				CalculatorList<UCM.Category> categories = m_model.GetCategories();
+				for (uint i = 0; i < categories.Size(); i++)
+				{
+					Category category = new Category(categories[i]);
+					m_Categories.Append(category);
+				}
 			}
 
 			RestoreUserPreferences();
@@ -1585,6 +1591,7 @@ namespace CalculatorApp.ViewModel
 		void RefreshSupplementaryResults()
 		{
 			lock (m_cacheMutex)
+			using(m_SupplementaryResults.BatchUpdate())
 			{
 				m_SupplementaryResults.Clear();
 
@@ -1607,7 +1614,6 @@ namespace CalculatorApp.ViewModel
 				{
 					m_SupplementaryResults.Append(whimsicals[0]);
 				}
-
 			}
 
 			RaisePropertyChanged(SupplementaryResultsPropertyName);