Desktop: swap the host lists in whole instead of announcing every row to listeners that redo all their work per row

src/DodoSSH.Client.Shell/ViewModels/TransfersViewModel.cs

@@ -867,14 +867,14 @@ internal sealed partial class TransfersViewModel : ObservableObject, IAsyncDispo
     /// not this object's to clear. The rows are shared: they carry the decrypted host, and copying that would
     /// be a second decrypted copy of a secret for no gain.
     /// </remarks>
-    internal ObservableCollection<HostRowViewModel> Hosts { get; } = [];
+    internal ReplaceableCollection<HostRowViewModel> Hosts { get; } = [];
 
     [ObservableProperty]
     private HostRowViewModel? selectedHost;
 
     /// <summary>The buckets that can be browsed, which is the vault's list.</summary>
     /// <inheritdoc cref="Hosts" path="/remarks" />
-    internal ObservableCollection<ObjectStoreRowViewModel> Buckets { get; } = [];
+    internal ReplaceableCollection<ObjectStoreRowViewModel> Buckets { get; } = [];
 
     [ObservableProperty]
     private ObjectStoreRowViewModel? selectedBucket;
@@ -3986,7 +3986,21 @@ internal sealed partial class TransfersViewModel : ObservableObject, IAsyncDispo
         }
     }
 
-    private void OnVaultListChanged(object? sender, NotifyCollectionChangedEventArgs e) => RefreshHosts();
+    /// <remarks>
+    /// Only the picker the list feeds. Refilling both on either list's change made every reload refill the host
+    /// picker once for the hosts and again for the buckets.
+    /// </remarks>
+    private void OnVaultListChanged(object? sender, NotifyCollectionChangedEventArgs e)
+    {
+        if (vault is { } open && ReferenceEquals(sender, open.ObjectStores))
+        {
+            RefreshPickers(hosts: false, buckets: true);
+        }
+        else
+        {
+            RefreshPickers(hosts: true, buckets: false);
+        }
+    }
 
     /// <summary>
     /// Rebuilds both pickers from the vault's lists.
@@ -4004,34 +4018,34 @@ internal sealed partial class TransfersViewModel : ObservableObject, IAsyncDispo
     /// connected to.
     /// </para>
     /// </remarks>
-    private void RefreshHosts()
+    private void RefreshHosts() => RefreshPickers(hosts: true, buckets: true);
+
+    private void RefreshPickers(bool hosts, bool buckets)
     {
         refreshingPickers = true;
 
         try
         {
-            Hosts.Clear();
-
             if (vault is not { } open)
             {
+                Hosts.ReplaceAll([]);
                 return;
             }
 
-            foreach (var row in open.Hosts)
+            if (hosts)
             {
-                Hosts.Add(row);
+                Hosts.ReplaceAll(open.Hosts);
+
+                SelectedHost = Hosts.FirstOrDefault(row => row.EntityId == chosenHost) ?? Hosts.FirstOrDefault();
             }
 
-            SelectedHost = Hosts.FirstOrDefault(row => row.EntityId == chosenHost) ?? Hosts.FirstOrDefault();
-
-            Buckets.Clear();
-
-            foreach (var row in open.ObjectStores)
+            if (buckets)
             {
-                Buckets.Add(row);
-            }
+                Buckets.ReplaceAll(open.ObjectStores);
 
-            SelectedBucket = Buckets.FirstOrDefault(row => row.EntityId == chosenBucket) ?? Buckets.FirstOrDefault();
+                SelectedBucket =
+                    Buckets.FirstOrDefault(row => row.EntityId == chosenBucket) ?? Buckets.FirstOrDefault();
+            }
         }
         finally
         {