Adjust project structure

src/Shared/HandyControl_Shared/Controls/Attach/PanelElement.cs

@@ -0,0 +1,44 @@
+using System.Windows;
+using System.Windows.Controls;
+using HandyControl.Interactivity;
+
+namespace HandyControl.Controls
+{
+    public class PanelElement
+    {
+        public static readonly DependencyProperty FluidMoveBehaviorProperty = DependencyProperty.RegisterAttached(
+            "FluidMoveBehavior", typeof(FluidMoveBehavior), typeof(PanelElement), new PropertyMetadata(default(FluidMoveBehavior), OnFluidMoveBehaviorChanged));
+
+        private static void OnFluidMoveBehaviorChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
+        {
+            if (d is Panel panel)
+            {                
+                var collection = Interaction.GetBehaviors(panel);
+                var oldBehavior = GetTempFluidMoveBehavior(panel);
+                collection.ItemRemoved(oldBehavior);
+                panel.SetCurrentValue(TempFluidMoveBehaviorProperty, DependencyProperty.UnsetValue);
+
+                if (e.NewValue is FluidMoveBehavior behavior)
+                {
+                    collection.ItemAdded(behavior);
+                    SetTempFluidMoveBehavior(panel, behavior);
+                }
+            }
+        }
+
+        public static void SetFluidMoveBehavior(DependencyObject element, FluidMoveBehavior value)
+            => element.SetValue(FluidMoveBehaviorProperty, value);
+
+        public static FluidMoveBehavior GetFluidMoveBehavior(DependencyObject element)
+            => (FluidMoveBehavior) element.GetValue(FluidMoveBehaviorProperty);
+
+        private static readonly DependencyProperty TempFluidMoveBehaviorProperty = DependencyProperty.RegisterAttached(
+            "TempFluidMoveBehavior", typeof(FluidMoveBehavior), typeof(PanelElement), new PropertyMetadata(default(FluidMoveBehavior)));
+
+        private static void SetTempFluidMoveBehavior(DependencyObject element, FluidMoveBehavior value)
+            => element.SetValue(TempFluidMoveBehaviorProperty, value);
+
+        private static FluidMoveBehavior GetTempFluidMoveBehavior(DependencyObject element)
+            => (FluidMoveBehavior) element.GetValue(TempFluidMoveBehaviorProperty);
+    }
+}