Fixes issue #398 where the Next / Previous buttons filed to work if the ScrollSnap was previously scrolling.

Also renamed the Extension Methods scripts and added a new function.

Resolves: #398

Runtime/Scripts/Layout/ScrollSnapBase.cs

@@ -5,6 +5,7 @@
 using System;
 using UnityEngine.Events;
 using UnityEngine.EventSystems;
+using UnityEngine.UI.Extensions;
 
 namespace UnityEngine.UI.Extensions
 {
@@ -314,6 +315,8 @@ namespace UnityEngine.UI.Extensions
         //Function for switching screens with buttons
         public void NextScreen()
         {
+            _scroll_rect.velocity = Vector2.zero;
+
             if (_currentPage < _screens - 1 || _isInfinite)
             {
                 if (!_lerp) StartScreenChange();
@@ -336,6 +339,8 @@ namespace UnityEngine.UI.Extensions
         //Function for switching screens with buttons
         public void PreviousScreen()
         {
+            _scroll_rect.velocity = Vector2.zero;
+
             if (_currentPage > 0 || _isInfinite)
             {
                 if (!_lerp) StartScreenChange();
@@ -515,15 +520,8 @@ namespace UnityEngine.UI.Extensions
                 MaskBuffer = 1;
             }
 
-            if (PageStep < 0)
+            PageStep.Clamp(0, 9);
-            {
-                PageStep = 0;
-            }
 
-            if (PageStep > 8)
-            {
-                PageStep = 9;
-            }
             var infiniteScroll = GetComponent<UI_InfiniteScroll>();
             if (ChildObjects != null && ChildObjects.Length > 0 && infiniteScroll != null && !infiniteScroll.InitByUser)
             {

Runtime/Scripts/Utilities/ExtensionMethods.cs

@@ -29,5 +29,27 @@ namespace UnityEngine.UI.Extensions
                 !gameObject.hideFlags.HasFlag(HideFlags.HideInHierarchy);
                     // I don't care about GameObjects *inside* prefabs, just the overall prefab.
         }
+
+        /// <summary>
+        /// Generic clamp method to limt a value between a range of values
+        /// </summary>
+        /// <typeparam name="T"><see cref="IComparable"/> data type</typeparam>
+        /// <param name="value">Value to clamp</param>
+        /// <param name="min">Minimum value</param>
+        /// <param name="max">Maximum value</param>
+        /// <returns></returns>
+        public static T Clamp<T>(this T value, T min, T max) where T : IComparable<T>
+        {
+            if (value.CompareTo(min) < 0)
+            {
+                value = min;
+            }
+            if (value.CompareTo(max) > 0)
+            {
+                value =  max;
+            }
+
+            return value;
+        }
     }
 }