Merge pull request #190 from EVEJay/master

Refactored to use pooling

Author: Slazanger

SMT/Helpers/CanvasExtensions.cs

@@ -0,0 +1,43 @@
+using System.Collections.Generic;
+using System.Linq;
+using System.Windows;
+using System.Windows.Controls;
+using System.Windows.Shapes;
+
+namespace SMT.Helpers;
+
+public static class CanvasExtensions
+{
+    public static void EnsureChild(this Canvas canvas, UIElement element)
+    {
+        if (element == null) return;
+        if (!canvas.Children.Contains(element))
+        {
+            canvas.Children.Add(element);
+        }
+    }
+    
+    public static void ClearChildren(this Canvas canvas, IList<UIElement> elements)
+    {
+        if (elements == null) return;
+        foreach (UIElement childElement in elements.ToList())
+        {
+            if (canvas.Children.Contains(childElement))
+            {
+                canvas.Children.Remove(childElement);
+            }
+        }
+        elements.Clear();
+    }
+
+    public static void ReleaseChildren<T>(this Canvas canvas, IList<T> elements, ElementPool<T> pool) where T : Shape, new()
+    {
+        if (elements == null) return;
+        foreach (T element in elements.ToList())
+        {
+            pool.Release(canvas, element);
+        }
+        elements.Clear();
+    }
+
+}

SMT/Helpers/ElementPool.cs

@@ -0,0 +1,48 @@
+using System.Collections.Generic;
+using System.Windows;
+using System.Windows.Controls;
+
+namespace SMT.Helpers;
+
+/// <summary>
+/// Simple Element pool for reusable UI Elements.
+/// </summary>
+/// <typeparam name="T">The pooled elements type, must be (derived from) Shape.</typeparam>
+public class ElementPool<T> where T : UIElement, new()
+{
+    private readonly Stack<T> _pool = new();
+
+    /// <summary>
+    /// Get an element out of the pool or create a new one
+    /// if there is none left.
+    /// </summary>
+    /// <returns>An element of the desired type.</returns>
+    public T Get()
+    {
+        if (_pool.Count > 0)
+        {
+            T item = _pool.Pop();
+            item.Visibility = Visibility.Visible;
+            return item;
+        }
+
+        return new T();
+    }
+
+    /// <summary>
+    /// Hides and element, removes it from the canvas and
+    /// returns it to the pool.
+    /// </summary>
+    /// <param name="canvas"></param>
+    /// <param name="item"></param>
+    public void Release(Canvas canvas, T item)
+    {
+        if (item == null) return;
+        item.Visibility = Visibility.Collapsed;
+        if (canvas.Children.Contains(item))
+        {
+            canvas.Children.Remove(item);
+        }
+        _pool.Push(item);
+    }
+}