From 7ee02c4b38da37f996e740e6821159d3c98ca8f4 Mon Sep 17 00:00:00 2001
From: "Frank A. Krueger" <fak@praeclarum.org>
Date: Mon, 16 Apr 2018 12:38:10 -0700
Subject: [PATCH] Add ScrollTo support to ScrollView

---
 Ooui.Forms/Renderers/ScrollViewRenderer.cs | 48 +++++++++++++++++++---
 1 file changed, 43 insertions(+), 5 deletions(-)

diff --git a/Ooui.Forms/Renderers/ScrollViewRenderer.cs b/Ooui.Forms/Renderers/ScrollViewRenderer.cs
index c364899..bbd3522 100644
--- a/Ooui.Forms/Renderers/ScrollViewRenderer.cs
+++ b/Ooui.Forms/Renderers/ScrollViewRenderer.cs
@@ -5,18 +5,56 @@ using Xamarin.Forms;
 
 namespace Ooui.Forms.Renderers
 {
-    public class ScrollViewRenderer : ViewRenderer<ScrollView, Div>
+    public class ScrollViewRenderer : VisualElementRenderer<ScrollView>
     {
+        bool disposed = false;
+
         protected override void OnElementChanged (ElementChangedEventArgs<ScrollView> e)
         {
-            base.OnElementChanged (e);
+            if (e.OldElement != null) {
+                e.OldElement.ScrollToRequested -= Element_ScrollToRequested;
+            }
 
-            this.Style.Overflow = "scroll";
+            if (e.NewElement != null) {
+                Style.Overflow = "scroll";
+
+                e.NewElement.ScrollToRequested += Element_ScrollToRequested;
+            }
+
+            base.OnElementChanged (e);
         }
 
-        protected override void OnElementPropertyChanged (object sender, PropertyChangedEventArgs e)
+        protected override void Dispose (bool disposing)
         {
-            base.OnElementPropertyChanged (sender, e);
+            base.Dispose (disposing);
+
+            if (disposing && !disposed) {
+                if (Element != null) {
+                    Element.ScrollToRequested -= Element_ScrollToRequested;
+                }
+                disposed = true;
+            }
+        }
+
+        void Element_ScrollToRequested (object sender, ScrollToRequestedEventArgs e)
+        {
+            var oe = (ITemplatedItemsListScrollToRequestedEventArgs)e;
+            var item = oe.Item;
+            var group = oe.Group;
+            if (e.Mode == ScrollToMode.Position) {
+                Send (Ooui.Message.Set (Id, "scrollTop", e.ScrollY));
+                Send (Ooui.Message.Set (Id, "scrollLeft", e.ScrollX));
+            }
+            else {
+                switch (e.Position) {
+                    case ScrollToPosition.Start:
+                        Send (Ooui.Message.Set (Id, "scrollTop", 0));
+                        break;
+                    case ScrollToPosition.End:
+                        Send (Ooui.Message.Set (Id, "scrollTop", new Ooui.Message.PropertyReference { TargetId = Id, Key = "scrollHeight" }));
+                        break;
+                }
+            }
         }
     }
 }