Anpassung am Sitzplan

LehrerApp.Desktop/Views/Groups/SeatingPlanTabView.axaml.cs

@@ -10,6 +10,9 @@ namespace LehrerApp.Desktop.Views.Groups;
 
 public partial class SeatingPlanTabView : UserControl
 {
+    private const double AutoScrollEdgeSize = 72;
+    private const double AutoScrollStep = 14;
+
     private object? _dragCandidate;
     private PointerPressedEventArgs? _dragTrigger;
     private Avalonia.Point _pressPosition;
@@ -18,8 +21,15 @@ public partial class SeatingPlanTabView : UserControl
     private SeatCellViewModel? _pendingDropTarget;
     private bool _pendingClearSeat;
     private DateTime _ignoreTapUntil;
+    private readonly DispatcherTimer _autoScrollTimer;
+    private Avalonia.Vector _autoScrollDirection;
 
-    public SeatingPlanTabView() => InitializeComponent();
+    public SeatingPlanTabView()
+    {
+        InitializeComponent();
+        _autoScrollTimer = new DispatcherTimer { Interval = TimeSpan.FromMilliseconds(30) };
+        _autoScrollTimer.Tick += OnAutoScrollTick;
+    }
 
     protected override void OnDataContextChanged(EventArgs e)
     {
@@ -69,6 +79,7 @@ public partial class SeatingPlanTabView : UserControl
         _draggedStudent = null;
         _pendingDropTarget = null;
         _pendingClearSeat = false;
+        StopAutoScroll();
         _ignoreTapUntil = DateTime.UtcNow.AddMilliseconds(250);
 
         // Never mutate an ItemsControl while Avalonia is still processing its native
@@ -107,6 +118,7 @@ public partial class SeatingPlanTabView : UserControl
 
     private void OnSeatDrop(object? sender, DragEventArgs e)
     {
+        StopAutoScroll();
         if (sender is not Border { DataContext: SeatCellViewModel target }) return;
         target.IsDropTarget = false;
         if (!CanDropOn(target))
@@ -128,6 +140,7 @@ public partial class SeatingPlanTabView : UserControl
 
     private void OnUnassignedDrop(object? sender, DragEventArgs e)
     {
+        StopAutoScroll();
         if (_draggedSeat is not null)
         {
             _pendingDropTarget = null;
@@ -136,6 +149,50 @@ public partial class SeatingPlanTabView : UserControl
         }
     }
 
+    private void OnRoomDragOver(object? sender, DragEventArgs e)
+    {
+        if (_draggedSeat is null && _draggedStudent is null)
+        {
+            StopAutoScroll();
+            return;
+        }
+
+        var position = e.GetPosition(RoomScrollViewer);
+        _autoScrollDirection = new Avalonia.Vector(
+            GetAutoScrollDirection(position.X, RoomScrollViewer.Bounds.Width),
+            GetAutoScrollDirection(position.Y, RoomScrollViewer.Bounds.Height));
+
+        if (_autoScrollDirection == default)
+            StopAutoScroll();
+        else if (!_autoScrollTimer.IsEnabled)
+            _autoScrollTimer.Start();
+    }
+
+    private void OnRoomDragLeave(object? sender, DragEventArgs e) => StopAutoScroll();
+
+    private void OnAutoScrollTick(object? sender, EventArgs e)
+    {
+        var maxX = Math.Max(0, RoomScrollViewer.Extent.Width - RoomScrollViewer.Viewport.Width);
+        var maxY = Math.Max(0, RoomScrollViewer.Extent.Height - RoomScrollViewer.Viewport.Height);
+        var offset = RoomScrollViewer.Offset;
+        RoomScrollViewer.Offset = new Avalonia.Vector(
+            Math.Clamp(offset.X + _autoScrollDirection.X * AutoScrollStep, 0, maxX),
+            Math.Clamp(offset.Y + _autoScrollDirection.Y * AutoScrollStep, 0, maxY));
+    }
+
+    private static double GetAutoScrollDirection(double position, double viewportSize)
+    {
+        if (position < AutoScrollEdgeSize) return -1;
+        if (position > viewportSize - AutoScrollEdgeSize) return 1;
+        return 0;
+    }
+
+    private void StopAutoScroll()
+    {
+        _autoScrollDirection = default;
+        _autoScrollTimer.Stop();
+    }
+
     private async void OnSeatTapped(object? sender, TappedEventArgs e)
     {
         if (DateTime.UtcNow < _ignoreTapUntil || sender is not Border { DataContext: SeatCellViewModel seat }