Display already loaded entries while loading files in a directory

Files/Files.csproj

@@ -150,6 +150,7 @@
       <DependentUpon>ConfirmDeleteDialog.xaml</DependentUpon>
     </Compile>
     <Compile Include="Helpers\AppTheme.cs" />
+    <Compile Include="Helpers\DispatcherHelper.cs" />
     <Compile Include="Helpers\ItemsDataTemplateSelector.cs" />
     <Compile Include="Helpers\NaturalStringComparer.cs" />
     <Compile Include="Helpers\StringExtensions.cs" />

Files/Helpers/DispatcherHelper.cs

@@ -0,0 +1,82 @@
+using System;
+using System.Runtime.CompilerServices;
+using Windows.UI.Core;
+
+namespace Files.Helpers
+{
+    /// <summary>
+    /// This class provides static methods helper for executing code in UI thread of the main window.
+    /// </summary>
+    static class DispatcherHelper
+    { /// <summary>
+      /// This struct represents an awaitable dispatcher.
+      /// </summary>
+        public struct DispatcherPriorityAwaitable
+        {
+            private readonly CoreDispatcher dispatcher;
+            private readonly CoreDispatcherPriority priority;
+
+            internal DispatcherPriorityAwaitable(CoreDispatcher dispatcher, CoreDispatcherPriority priority)
+            {
+                this.dispatcher = dispatcher;
+                this.priority = priority;
+            }
+
+            /// <summary>
+            /// Get awaiter of DispatcherPriorityAwaiter
+            /// </summary>
+            /// <returns>Awaiter of DispatcherPriorityAwaiter</returns>
+            public DispatcherPriorityAwaiter GetAwaiter()
+            {
+                return new DispatcherPriorityAwaiter(this.dispatcher, this.priority);
+            }
+        }
+
+        /// <summary>
+        /// This struct represents the awaiter of a dispatcher.
+        /// </summary>
+        public struct DispatcherPriorityAwaiter : INotifyCompletion
+        {
+            private readonly CoreDispatcher dispatcher;
+            private readonly CoreDispatcherPriority priority;
+
+            /// <summary>
+            /// Gets a value indicating whether task has completed
+            /// </summary>
+            public bool IsCompleted => false;
+
+            internal DispatcherPriorityAwaiter(CoreDispatcher dispatcher, CoreDispatcherPriority priority)
+            {
+                this.dispatcher = dispatcher;
+                this.priority = priority;
+            }
+
+            /// <summary>
+            /// Get result for this awaiter
+            /// </summary>
+            public void GetResult()
+            {
+            }
+
+            /// <summary>
+            /// Fired once task has complated for notify completion
+            /// </summary>
+            /// <param name="continuation">Continuation action</param>
+            public async void OnCompleted(Action continuation)
+            {
+                await this.dispatcher.RunAsync(this.priority, new DispatchedHandler(continuation));
+            }
+        }
+
+        /// <summary>
+        /// Yield and allow UI update during tasks.
+        /// </summary>
+        /// <param name="dispatcher">Dispatcher of a thread to yield</param>
+        /// <param name="priority">Dispatcher execution priority, default is low</param>
+        /// <returns>Awaitable dispatcher task</returns>
+        public static DispatcherPriorityAwaitable YieldAsync(this CoreDispatcher dispatcher, CoreDispatcherPriority priority = CoreDispatcherPriority.Low)
+        {
+            return new DispatcherPriorityAwaitable(dispatcher, priority);
+        }
+    }
+}

Files/View Models/ItemViewModel.cs

@@ -33,7 +33,7 @@
 
 namespace Files.Filesystem
 {
-    public class ItemViewModel : INotifyPropertyChanged
+    public class ItemViewModel : INotifyPropertyChanged, IDisposable
     {
         public EmptyFolderTextState EmptyTextState { get; set; } = new EmptyFolderTextState();
         public LoadingIndicator LoadIndicator { get; set; } = new LoadingIndicator();
@@ -448,9 +448,16 @@ public void OrderFiles()
                     ordered = ordered.ThenByDescending(orderByNameFunc, naturalStringComparer);
             }
             orderedList = ordered.ToList();
-            _filesAndFolders.Clear();
-            foreach (ListedItem i in orderedList)
-                _filesAndFolders.Add(i);
+
+            List<ListedItem> originalList = _filesAndFolders.ToList();
+            for (var i = 0; i < originalList.Count; i++)
+            {
+                if (originalList[i] != orderedList[i])
+                {
+                    _filesAndFolders.RemoveAt(i);
+                    _filesAndFolders.Insert(i, orderedList[i]);
+                }
+            }
         }
 
         public static T GetCurrentSelectedTabInstance<T>()
@@ -742,6 +749,15 @@ public async Task RapidAddItemsToCollectionAsync(string path)
                             }
                         }
                     }
+                    if (_cancellationTokenSource.IsCancellationRequested)
+                    {
+                        break;
+                    }
+
+                    if (count % 64 == 0)
+                    {
+                        await CoreApplication.MainView.CoreWindow.Dispatcher.YieldAsync();
+                    }
                 } while (FindNextFile(hFile, out findData));
 
                 FindClose(hFile);
@@ -751,6 +767,7 @@ public async Task RapidAddItemsToCollectionAsync(string path)
             {
                 if (_cancellationTokenSource.IsCancellationRequested)
                 {
+                    _cancellationTokenSource.Dispose();
                     _cancellationTokenSource = new CancellationTokenSource();
                     IsLoadingItems = false;
                     return;
@@ -1139,5 +1156,10 @@ private void NotifyPropertyChanged([CallerMemberName] string propertyName = "")
             }
             PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
         }
+
+        public void Dispose()
+        {
+            _cancellationTokenSource?.Dispose();
+        }
     }
 }

Files/View Models/SettingsViewModel.cs

@@ -314,7 +314,7 @@ private async void LoadTerminalApps()
             //        await FileIO.WriteTextAsync(file, JsonConvert.SerializeObject(terminalsFileModel, Formatting.Indented));
             //    }
             //}
-            Terminals = terminalsFileModel.Terminals;
+            Terminals = terminalsFileModel?.Terminals ?? new List<TerminalModel>();
         }
 
         private IList<TerminalModel> _Terminals = null;