feat: complete UM Trace iOS and field UI integration

FieldLogger/ViewModels/JobsViewModel.cs

@@ -40,41 +40,112 @@ public sealed partial class JobsViewModel : ObservableObject
 {
     private readonly AppDatabase _database;
     private readonly SettingsService _settings;
+    private readonly SemaphoreSlim _refreshGate = new(1, 1);
 
     public ObservableCollection<JobListItem> Jobs { get; } = new();
 
     [ObservableProperty]
     private bool _isBusy;
 
+    [ObservableProperty]
+    private bool _isRefreshing;
+
     public JobsViewModel(AppDatabase database, SettingsService settings)
     {
         _database = database;
         _settings = settings;
     }
 
+    public Task LoadAsync()
+        => ReloadAsync(showRefreshIndicator: false, skipIfBusy: true);
+
     [RelayCommand]
-    public async Task RefreshAsync()
+    private Task RefreshAsync()
+        => ReloadAsync(showRefreshIndicator: true, skipIfBusy: false);
+
+    private async Task ReloadAsync(bool showRefreshIndicator, bool skipIfBusy)
     {
-        IsBusy = true;
+        var entered = skipIfBusy
+            ? await _refreshGate.WaitAsync(0)
+            : await WaitForRefreshGateAsync();
+        if (!entered)
+            return;
+
         try
         {
+            IsBusy = true;
+            if (showRefreshIndicator)
+                IsRefreshing = true;
+
             var jobs = await _database.GetJobsAsync();
             var activeId = _settings.ActiveJobId;
 
-            Jobs.Clear();
+            // Build a snapshot off-screen, then reconcile it with the existing observable
+            // collection. Keeping the existing rows prevents CollectionView from repeatedly
+            // discarding its measured cells and jumping back to the top.
+            var items = new List<JobListItem>(jobs.Count);
             foreach (var job in jobs)
             {
-                Jobs.Add(new JobListItem
+                items.Add(new JobListItem
                 {
                     Job = job,
                     PointCount = await _database.GetPointCountAsync(job.Id),
                     IsActive = job.Id == activeId,
                 });
             }
+
+            ApplySnapshot(items);
         }
         finally
         {
+            if (showRefreshIndicator)
+                IsRefreshing = false;
             IsBusy = false;
+            _refreshGate.Release();
+        }
+    }
+
+    private async Task<bool> WaitForRefreshGateAsync()
+    {
+        await _refreshGate.WaitAsync();
+        return true;
+    }
+
+    private void ApplySnapshot(IReadOnlyList<JobListItem> incoming)
+    {
+        var incomingIds = incoming.Select(item => item.Job.Id).ToHashSet();
+
+        for (var index = Jobs.Count - 1; index >= 0; index--)
+        {
+            if (!incomingIds.Contains(Jobs[index].Job.Id))
+                Jobs.RemoveAt(index);
+        }
+
+        for (var targetIndex = 0; targetIndex < incoming.Count; targetIndex++)
+        {
+            var replacement = incoming[targetIndex];
+            var existingIndex = -1;
+            for (var index = targetIndex; index < Jobs.Count; index++)
+            {
+                if (Jobs[index].Job.Id == replacement.Job.Id)
+                {
+                    existingIndex = index;
+                    break;
+                }
+            }
+
+            if (existingIndex < 0)
+            {
+                Jobs.Insert(targetIndex, replacement);
+                continue;
+            }
+
+            var existing = Jobs[existingIndex];
+            existing.PointCount = replacement.PointCount;
+            existing.IsActive = replacement.IsActive;
+
+            if (existingIndex != targetIndex)
+                Jobs.Move(existingIndex, targetIndex);
         }
     }
 
@@ -101,7 +172,7 @@ public sealed partial class JobsViewModel : ObservableObject
             _settings.ActiveJobId = job.Id;
             Console.WriteLine($"NewJobAsync: Set active job to {job.Id}");
 
-            await RefreshAsync();
+            await ReloadAsync(showRefreshIndicator: false, skipIfBusy: false);
             Console.WriteLine("NewJobAsync: Refresh complete");
         }
         catch (Exception ex)
@@ -135,6 +206,6 @@ public sealed partial class JobsViewModel : ObservableObject
         await _database.DeleteJobAsync(item.Job.Id);
         if (_settings.ActiveJobId == item.Job.Id)
             _settings.ActiveJobId = null;
-        await RefreshAsync();
+        await ReloadAsync(showRefreshIndicator: false, skipIfBusy: false);
     }
 }