From 79e4e87b9560a9dbccb2928d8932c44fe0dee24f Mon Sep 17 00:00:00 2001
From: "Frank A. Krueger" <fak@praeclarum.org>
Date: Sun, 15 Apr 2018 22:55:23 -0700
Subject: [PATCH] Add some ScrollTo support to ListView

---
 Ooui.Forms/Extensions/FontExtensions.cs  |  2 +-
 Ooui.Forms/Renderers/ListViewRenderer.cs | 21 +++++++++++++++++++++
 Ooui/Client.js                           |  4 ++++
 Ooui/Message.cs                          | 16 ++++++++++++++++
 Samples/ListView/RefreshListView.xaml    |  6 ++++--
 Samples/ListView/RefreshListView.xaml.cs |  7 +++++++
 6 files changed, 53 insertions(+), 3 deletions(-)

diff --git a/Ooui.Forms/Extensions/FontExtensions.cs b/Ooui.Forms/Extensions/FontExtensions.cs
index f4c5860..4776f83 100644
--- a/Ooui.Forms/Extensions/FontExtensions.cs
+++ b/Ooui.Forms/Extensions/FontExtensions.cs
@@ -77,7 +77,7 @@ namespace Ooui.Forms.Extensions
                 }
                 else {
                     if (c == ' ') {
-                        if (i >= lineStartIndex && text[i-1] != ' ')
+                        if (i >= lineStartIndex && i > 0 && text[i-1] != ' ')
                             firstSpaceX = px;
                         lastSpaceIndex = i;
                     }
diff --git a/Ooui.Forms/Renderers/ListViewRenderer.cs b/Ooui.Forms/Renderers/ListViewRenderer.cs
index 95b18f1..5dd5482 100644
--- a/Ooui.Forms/Renderers/ListViewRenderer.cs
+++ b/Ooui.Forms/Renderers/ListViewRenderer.cs
@@ -27,6 +27,7 @@ namespace Ooui.Forms.Renderers
             {
                 var templatedItems = TemplatedItemsView.TemplatedItems;
                 templatedItems.CollectionChanged -= OnCollectionChanged;
+                e.OldElement.ScrollToRequested -= ListView_ScrollToRequested;
             }
 
             if (e.NewElement != null)
@@ -41,6 +42,7 @@ namespace Ooui.Forms.Renderers
 
                 var templatedItems = TemplatedItemsView.TemplatedItems;
                 templatedItems.CollectionChanged += OnCollectionChanged;
+                e.NewElement.ScrollToRequested += ListView_ScrollToRequested;
 
                 UpdateItems ();
                 UpdateBackgroundColor();
@@ -70,6 +72,7 @@ namespace Ooui.Forms.Renderers
                 {
                     var templatedItems = TemplatedItemsView.TemplatedItems;
                     templatedItems.CollectionChanged -= OnCollectionChanged;
+                    Element.ScrollToRequested -= ListView_ScrollToRequested;
                 }
 
                 _disposed = true;
@@ -139,6 +142,24 @@ namespace Ooui.Forms.Renderers
             Element.NotifyRowTapped(ndx, null);
         }
 
+        void ListView_ScrollToRequested (object sender, ScrollToRequestedEventArgs e)
+        {
+            if (Control == null)
+                return;
+            
+            var oe = (ITemplatedItemsListScrollToRequestedEventArgs)e;
+            var item = oe.Item;
+            var group = oe.Group;
+            switch (e.Position) {
+                case ScrollToPosition.Start:
+                    Control.Send (Ooui.Message.Set (Control.Id, "scrollTop", 0));
+                    break;
+                case ScrollToPosition.End:
+                    Control.Send (Ooui.Message.Set (Control.Id, "scrollTop", new Ooui.Message.PropertyReference { TargetId = Control.Id, Key = "scrollHeight" }));
+                    break;
+            }
+        }
+
         private void UpdateBackgroundColor()
         {
             var backgroundColor = Element.BackgroundColor.ToOouiColor();
diff --git a/Ooui/Client.js b/Ooui/Client.js
index 4b1f998..7a271ef 100644
--- a/Ooui/Client.js
+++ b/Ooui/Client.js
@@ -295,6 +295,7 @@ function processMessage (m) {
 }
 
 function fixupValue (v) {
+    var x, n;
     if (Array.isArray (v)) {
         for (x in v) {
             v[x] = fixupValue (v[x]);
@@ -307,6 +308,9 @@ function fixupValue (v) {
             return getNode (v);
         }
     }
+    else if (!!v && v.hasOwnProperty("id") && v.hasOwnProperty("k")) {
+        return fixupValue(v["id"])[v["k"]];
+    }
     return v;
 }
 
diff --git a/Ooui/Message.cs b/Ooui/Message.cs
index 5db69af..3aa9c1e 100644
--- a/Ooui/Message.cs
+++ b/Ooui/Message.cs
@@ -29,6 +29,13 @@ namespace Ooui
             Value = args,
         };
 
+        public static Message Set (string targetId, string property, object value) => new Message {
+            MessageType = MessageType.Set,
+            TargetId = targetId,
+            Key = property,
+            Value = value,
+        };
+
         public static Message Event (string targetId, string eventType, object value = null) => new Message {
             MessageType = MessageType.Event,
             TargetId = targetId,
@@ -36,6 +43,15 @@ namespace Ooui
             Value = value,
         };
 
+        public class PropertyReference
+        {
+            [JsonProperty ("id")]
+            public string TargetId = "";
+
+            [JsonProperty ("k")]
+            public string Key = "";
+        }
+
         public void WriteJson (System.IO.TextWriter w)
         {
             w.Write ('{');
diff --git a/Samples/ListView/RefreshListView.xaml b/Samples/ListView/RefreshListView.xaml
index 45eb936..2c69c9e 100644
--- a/Samples/ListView/RefreshListView.xaml
+++ b/Samples/ListView/RefreshListView.xaml
@@ -1,4 +1,4 @@
-<?xml version="1.0" encoding="utf-8" ?>
+<?xml version="1.0" encoding="utf-8" ?>
 <ContentPage
     xmlns="http://xamarin.com/schemas/2014/forms"
     xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
@@ -6,6 +6,7 @@
     <ContentPage.Content>
         <StackLayout>
             <ListView
+                x:Name="list"
                 ItemsSource="{Binding Data}"
                 HeightRequest="200">
                 <ListView.ItemTemplate>
@@ -22,7 +23,8 @@
                     Text="{Binding Input}" />
                 <Button
                     Text="Add Item"
-                    Command="{Binding AddCmd}" />
+                    Command="{Binding AddCmd}"
+                Clicked="Handle_Clicked"/>
             </StackLayout>
         </StackLayout>
     </ContentPage.Content>
diff --git a/Samples/ListView/RefreshListView.xaml.cs b/Samples/ListView/RefreshListView.xaml.cs
index 4dd02f5..8c10031 100644
--- a/Samples/ListView/RefreshListView.xaml.cs
+++ b/Samples/ListView/RefreshListView.xaml.cs
@@ -1,5 +1,6 @@
 using Xamarin.Forms;
 using Xamarin.Forms.Xaml;
+using System.Linq;
 
 namespace Samples
 {
@@ -12,5 +13,11 @@ namespace Samples
 
             BindingContext = new RefreshListViewModel ();
         }
+
+        void Handle_Clicked (object sender, System.EventArgs e)
+        {
+            string item = ((RefreshListViewModel)BindingContext).Data.LastOrDefault ();
+            list.ScrollTo (item, ScrollToPosition.End, true);
+        }
 	}
 }