From 36882961fed857efccdbb11ad493aa6cc15f6fe8 Mon Sep 17 00:00:00 2001
From: Dan Walmsley <dan@walms.co.uk>
Date: Tue, 19 Nov 2024 14:32:54 +0000
Subject: [PATCH 1/2] Behavior to nudge items out the way during drag drop
 operations.

---
 .../ItemsControl/ItemNudgeDropBehavior.cs     | 88 +++++++++++++++++++
 1 file changed, 88 insertions(+)
 create mode 100644 src/Avalonia.Xaml.Interactions.Custom/ItemsControl/ItemNudgeDropBehavior.cs

diff --git a/src/Avalonia.Xaml.Interactions.Custom/ItemsControl/ItemNudgeDropBehavior.cs b/src/Avalonia.Xaml.Interactions.Custom/ItemsControl/ItemNudgeDropBehavior.cs
new file mode 100644
index 00000000..19bf5f35
--- /dev/null
+++ b/src/Avalonia.Xaml.Interactions.Custom/ItemsControl/ItemNudgeDropBehavior.cs
@@ -0,0 +1,88 @@
+using Avalonia.Controls;
+using Avalonia.Input;
+using Avalonia.Interactivity;
+using Avalonia.Layout;
+using Avalonia.Media.Transformation;
+using Avalonia.Xaml.Interactivity;
+
+namespace Avalonia.Xaml.Interactions.Custom;
+
+public class ItemNudgeDropBehavior : StyledElementBehavior<ItemsControl>
+{
+    public static readonly StyledProperty<Orientation> OrientationProperty =
+        AvaloniaProperty.Register<ItemNudgeDropBehavior, Orientation>(nameof(Orientation),
+            defaultValue: Orientation.Vertical);
+
+    public Orientation Orientation
+    {
+        get => GetValue(OrientationProperty);
+        set => SetValue(OrientationProperty, value);
+    }
+
+    /// <inheritdoc />
+    protected override void OnAttachedToVisualTree()
+    {
+        AssociatedObject?.AddHandler(DragDrop.DragLeaveEvent, OnDragLeave);
+        AssociatedObject?.AddHandler(DragDrop.DragOverEvent, OnDragOver);
+        AssociatedObject?.AddHandler(DragDrop.DropEvent, OnDrop);
+    }
+
+    /// <inheritdoc />
+    protected override void OnDetachedFromVisualTree()
+    {
+        AssociatedObject?.RemoveHandler(DragDrop.DragLeaveEvent, OnDragLeave);
+        AssociatedObject?.RemoveHandler(DragDrop.DragOverEvent, OnDragOver);
+        AssociatedObject?.RemoveHandler(DragDrop.DropEvent, OnDrop);
+    }
+    
+    private void ApplyTranslation(Control control, double x, double y)
+    {
+        var transformBuilder = new TransformOperations.Builder(1);
+        transformBuilder.AppendTranslate(x, y);
+        control.RenderTransform = transformBuilder.Build();
+    }
+    
+    private void RemoveTranslations(object? sender)
+    {
+        if (sender is ItemsControl itemsControl)
+        {
+            foreach (var container in itemsControl.GetRealizedContainers())
+            {
+                ApplyTranslation(container, 0, 0);
+            }
+        }
+    }
+    
+    private void OnDrop(object? sender, DragEventArgs e)
+    {
+        RemoveTranslations(sender);
+    }
+
+    private void OnDragLeave(object? sender, RoutedEventArgs e)
+    {
+        RemoveTranslations(sender);
+    }
+
+    private void OnDragOver(object? sender, DragEventArgs e)
+    {
+        if (sender is not ItemsControl itemsControl) return;
+
+        var isHorizontal = Orientation == Orientation.Horizontal;
+
+        var dragPosition = e.GetPosition(itemsControl);
+
+        for (int index = 0; index < itemsControl.ItemCount; index++)
+        {
+            var container = itemsControl.ContainerFromIndex(index);
+
+            if (container == null) continue;
+            
+            var containerMidPoint = isHorizontal ? container.Bounds.Center.X : container.Bounds.Center.Y;
+            
+            var translationX = isHorizontal && dragPosition.X <= containerMidPoint ? container.Bounds.Width : 0;
+            var translationY = !isHorizontal && dragPosition.Y <= containerMidPoint ? container.Bounds.Height : 0;
+
+            ApplyTranslation(container, translationX, translationY);
+        }
+    }
+}

From fee71e271cac6d10459d1f014d6e4f5638708be7 Mon Sep 17 00:00:00 2001
From: Dan Walmsley <dan@walms.co.uk>
Date: Tue, 19 Nov 2024 14:35:58 +0000
Subject: [PATCH 2/2] comments

---
 .../ItemsControl/ItemNudgeDropBehavior.cs                | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/src/Avalonia.Xaml.Interactions.Custom/ItemsControl/ItemNudgeDropBehavior.cs b/src/Avalonia.Xaml.Interactions.Custom/ItemsControl/ItemNudgeDropBehavior.cs
index 19bf5f35..9c5b690e 100644
--- a/src/Avalonia.Xaml.Interactions.Custom/ItemsControl/ItemNudgeDropBehavior.cs
+++ b/src/Avalonia.Xaml.Interactions.Custom/ItemsControl/ItemNudgeDropBehavior.cs
@@ -7,12 +7,21 @@
 
 namespace Avalonia.Xaml.Interactions.Custom;
 
+/// <summary>
+/// 
+/// </summary>
 public class ItemNudgeDropBehavior : StyledElementBehavior<ItemsControl>
 {
+    /// <summary>
+    /// 
+    /// </summary>
     public static readonly StyledProperty<Orientation> OrientationProperty =
         AvaloniaProperty.Register<ItemNudgeDropBehavior, Orientation>(nameof(Orientation),
             defaultValue: Orientation.Vertical);
 
+    /// <summary>
+    /// 
+    /// </summary>
     public Orientation Orientation
     {
         get => GetValue(OrientationProperty);