Make ChangedFilesTree a read-only list.

Rather than using a reactive list and clearing and rebuilding on
refresh, expose a read-only list and completely replace it on refresh.
This prevents the UI jumping around as the list is cleared and rebuilt.

Author: grokys

src/GitHub.App/SampleData/PullRequestDetailViewModelDesigner.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Collections.Generic;
 using System.Diagnostics.CodeAnalysis;
 using System.Reactive;
 using System.Threading.Tasks;
@@ -27,6 +28,8 @@ public class PullRequestUpdateStateDesigner : IPullRequestUpdateState
     [ExcludeFromCodeCoverage]
     public class PullRequestDetailViewModelDesigner : PanePageViewModelBase, IPullRequestDetailViewModel
     {
+        private List<IPullRequestChangeNode> changedFilesTree;
+
         public PullRequestDetailViewModelDesigner()
         {
             var repoPath = @"C:\Repo";
@@ -63,8 +66,8 @@ public PullRequestDetailViewModelDesigner()
             modelsDir.Files.Add(oldBranchModel);
             gitHubDir.Directories.Add(modelsDir);
 
-            ChangedFilesTree = new ReactiveList<IPullRequestChangeNode>();
-            ChangedFilesTree.Add(gitHubDir);
+            changedFilesTree = new List<IPullRequestChangeNode>();
+            changedFilesTree.Add(gitHubDir);
         }
 
         public IPullRequestModel Model { get; }
@@ -74,7 +77,7 @@ public PullRequestDetailViewModelDesigner()
         public bool IsBusy { get; }
         public bool IsFromFork { get; }
         public string Body { get; }
-        public IReactiveList<IPullRequestChangeNode> ChangedFilesTree { get; }
+        public IReadOnlyList<IPullRequestChangeNode> ChangedFilesTree => changedFilesTree;
         public IPullRequestCheckoutState CheckoutState { get; set; }
         public IPullRequestUpdateState UpdateState { get; set; }
         public string OperationError { get; set; }

src/GitHub.App/ViewModels/PullRequestDetailViewModel.cs

@@ -35,6 +35,7 @@ public class PullRequestDetailViewModel : PanePageViewModelBase, IPullRequestDet
         string sourceBranchDisplayName;
         string targetBranchDisplayName;
         string body;
+        IReadOnlyList<IPullRequestChangeNode> changedFilesTree;
         IPullRequestCheckoutState checkoutState;
         IPullRequestUpdateState updateState;
         string operationError;
@@ -213,7 +214,11 @@ public string OperationError
         /// <summary>
         /// Gets the changed files as a tree.
         /// </summary>
-        public IReactiveList<IPullRequestChangeNode> ChangedFilesTree { get; } = new ReactiveList<IPullRequestChangeNode>();
+        public IReadOnlyList<IPullRequestChangeNode> ChangedFilesTree
+        {
+            get { return changedFilesTree; }
+            private set { this.RaiseAndSetIfChanged(ref changedFilesTree, value); }
+        }
 
         /// <summary>
         /// Gets a command that checks out the pull request locally.
@@ -280,15 +285,8 @@ public async Task Load(IPullRequestModel pullRequest)
             TargetBranchDisplayName = GetBranchDisplayName(IsFromFork, pullRequest.Base.Label);
             Body = !string.IsNullOrWhiteSpace(pullRequest.Body) ? pullRequest.Body : Resources.NoDescriptionProvidedMarkdown;
 
-            ChangedFilesTree.Clear();
-
-            var treeChanges = await pullRequestsService.GetTreeChanges(repository, pullRequest);
-
-            // WPF doesn't support AddRange here so iterate through the changes.
-            foreach (var change in CreateChangedFilesTree(pullRequest, treeChanges).Children)
-            {
-                ChangedFilesTree.Add(change);
-            }
+            var changes = await pullRequestsService.GetTreeChanges(repository, pullRequest);
+            ChangedFilesTree = CreateChangedFilesTree(pullRequest, changes).Children.ToList();
 
             var localBranches = await pullRequestsService.GetLocalBranches(repository, pullRequest).ToList();
             var isCheckedOut = localBranches.Contains(repository.CurrentBranch);

src/GitHub.Exports.Reactive/ViewModels/IPullRequestDetailViewModel.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Collections.Generic;
 using System.Reactive;
 using System.Threading.Tasks;
 using GitHub.Models;
@@ -92,7 +93,7 @@ public interface IPullRequestDetailViewModel : IViewModel, IHasLoading, IHasBusy
         /// <summary>
         /// Gets the changed files as a tree.
         /// </summary>
-        IReactiveList<IPullRequestChangeNode> ChangedFilesTree { get; }
+        IReadOnlyList<IPullRequestChangeNode> ChangedFilesTree { get; }
 
         /// <summary>
         /// Gets the state associated with the <see cref="Checkout"/> command.