Allow resetting VirtualizedDynamicScrollRectList (#540)

org.mixedrealitytoolkit.uxcore/Experimental/List/VirtualizedScrollRectList.cs

@@ -156,6 +156,7 @@ public enum Layout
         private float contentStart;
         private float layoutPrefabSize;
         private bool initialized = false;
+        private bool resetCalled = false;
 
         private int visibleStart;
         private int visibleEnd;
@@ -164,6 +165,8 @@ public enum Layout
         private Queue<GameObject> pool = new Queue<GameObject>();
         private Dictionary<int, GameObject> poolDict = new Dictionary<int, GameObject>();
 
+        private Action<GameObject, int> onVisible;
+        private Action<GameObject, int> onInvisible;
         #endregion
 
         #region Public properties and fields
@@ -190,6 +193,24 @@ public float Scroll
             }
         }
 
+        /// <summary>
+        /// The pool of list item objects will be composed of this Prefab. When
+        /// the value changes the items are all repopulated.
+        /// <see cref="ResetLayout"/>
+        /// </summary>
+        public GameObject Prefab
+        {
+            get => prefab;
+            set
+            {
+                if (prefab != value)
+                {
+                    prefab = value;
+                    ResetLayout();
+                }
+            }
+        }
+
         /// <summary>
         /// This is the current number of items that this list is handling for
         /// display.
@@ -236,18 +257,44 @@ public float Scroll
         /// content area, this callback is called, with an integer representing
         /// the index of the item in the list. This callback is invoked after
         /// the GameObject has been positioned, but just before it is made
-        /// visible.
+        /// visible. When the value is set the list of items get reset.
+        /// <see cref="ResetLayout"/>.
         /// </summary>
-        public Action<GameObject, int> OnVisible { get; set; }
+        public Action<GameObject, int> OnVisible
+        {
+            get => onVisible;
+            set
+            {
+                if (onVisible != value)
+                {
+                    onVisible = value;
+                    // If this is changeing, it means how the items are populated is changing, hence reset.
+                    ResetLayout();
+                }
+            }
+        }
 
         /// <summary>
         /// When a pooled prefab instance is just removed from visibility on
         /// the scroll content area, this callback is called, with an integer
         /// representing the index of the item in the list. VirtualizedScrollRectList
         /// will make this GameObject invisible for you after this callback is
-        /// invoked.
+        /// invoked. When the value is set the list of items get reset
+        /// <see cref="ResetLayout"/>.
         /// </summary>
-        public Action<GameObject, int> OnInvisible { get; set; }
+        public Action<GameObject, int> OnInvisible
+        {
+            get => onInvisible;
+            set
+            {
+                if (onInvisible != value)
+                {
+                    onInvisible = value;
+                    // If this is changeing, it means how the items are populated is changing, hence reset.
+                    ResetLayout();
+                }
+            }
+        }
 
         #endregion
 
@@ -313,14 +360,7 @@ private float ScrollToPos(float scroll) => layoutDirection == Layout.Vertical
         /// </summary>
         private void OnValidate()
         {
-            // We only want to reset things if it has already been initialized,
-            // we don't want to initialize it prematurely!
-            if (initialized == false) { return; }
-
-            if (margin < gutter) { margin = gutter; }
-
-            visibleValid = false;
-            Initialize();
+            ResetLayout();
         }
 
         /// <summary>
@@ -394,7 +434,7 @@ private void Initialize()
 
         private void InitializePool()
         {
-            // Support resetting everything from OnValidate
+            // Support resetting everything from ResetLayout
             foreach (int i in poolDict.Keys.ToArray())
             {
                 MakeInvisible(i);
@@ -484,6 +524,15 @@ private void MakeVisible(int i)
             OnVisible?.Invoke(go, i);
         }
 
+        private IEnumerator ResetLayoutAtEndOfFrame()
+        {
+            yield return new WaitForEndOfFrame();
+            if (margin < gutter) { margin = gutter; }
+
+            resetCalled = false;
+            visibleValid = false;
+            Initialize();
+        }
         #endregion
 
         #region Public Methods
@@ -531,6 +580,27 @@ public void SetItemCount(int newCount)
             visibleValid = false;
             UpdateScrollView(scroll);
         }
+
+        /// <summary>
+        /// Resets the VirtualizedScrollRectList. This may remove items aready
+        /// visible and create new items.
+        /// </summary>
+        public void ResetLayout()
+        {
+            // We only want to reset things if it has already been initialized,
+            // we don't want to initialize it prematurely!
+            if (initialized == false)
+            {
+                return;
+            }
+
+            // We don't want to reset multiple times in one frame.
+            if (resetCalled)
+            {
+                return;
+            }
+            StartCoroutine(ResetLayoutAtEndOfFrame());
+        }
         #endregion
     }
 }

org.mixedrealitytoolkit.uxcore/Tests/Runtime/Prefabs/ScrollTestItem.prefab

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