fix memory leak on Android CollectionView

Author: roubachof

README.md

@@ -107,6 +107,61 @@ For example, you can add a shadow to a rounded button:
 
 <img src="Docs/rounded_button.png" height="180"/>
 
+### Choose your Shade Collection
+
+You can use several type of `IEnumerable<Shade>`:
+
+#### 1. ReadOnlyCollection<Shade>
+
+This is what you want to use most of the time.
+All the different `IMarkupExtension` like `ImmutableShades, NeumorphismShades, SingleShade`, return a `ReadOnlyCollection<Shade>`.
+If you use a `ReadOnlyCollection<Shade>`, all shades will be cloned to be sure the immutability is respected.
+It means, you can specify shades as static objects in your `ResourceDictionary`, it won't create any leak or view hierarchy issues.
+
+```xml
+<ResourceDictionary xmlns="http://xamarin.com/schemas/2014/forms"
+                    xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+                    xmlns:sh="clr-namespace:Sharpnado.Shades;assembly=Sharpnado.Shadows">
+    <sh:SingleShade x:Key="ShadowTop"
+                    BlurRadius="6"
+                    Opacity="0.15"
+                    Offset="0,-8"
+                    Color="{StaticResource ShadowsColor}" />
+
+    <sh:SingleShade x:Key="ShadowBottom"
+                    BlurRadius="6"
+                    Opacity="0.1"
+                    Offset="0,5"
+                    Color="{StaticResource ShadowsColor}" />
+
+    <sh:SingleShade x:Key="ShadowAccentBottom"
+                    BlurRadius="6"
+                    Opacity="0.4"
+                    Offset="0,4"
+                    Color="{StaticResource AccentColor}" />
+
+    <sh:ImmutableShades x:Key="ShadowNone" />
+
+    <sh:NeumorphismShades x:Key="ShadowNeumorphism" />
+
+    <sh:NeumorphismShades x:Key="ShadowThinNeumorphism"
+                          LowerOffset="8, 6"
+                          UpperOffset="-8,-6" />
+</ResourceDictionary>
+```
+
+#### 2. ObservableCollection<Shade>
+
+Only if you want to dynamically add or remove shade during the view lifetime.
+
+#### 3. All other IEnumerable<Shade>
+
+If you want to modify a shade property during the view lifetime.
+
+**IMPORTANT**: if you don't use a `ReadOnlyCollection<Shade>` please be sure to declare your `Shade` as transient. 
+It means you should declare a new instance of `Shade` for each `Shadows` views. For example, in code-behind with `new Shade()`, or in xaml with `Shades` property. 
+Just don't reference static instances of shade from `ResourceDictionary` with `StaticResource` references, or even in a C# class.
+
 ### Shades
 
 The `Shadows` component has only 2 properties:
@@ -252,8 +307,8 @@ Have a look at the `BeCreative.xaml` file and its code-behind.
 
 To have a better control of your shades, `Shadows` provides 2 kinds of `MarkupExtension`:
 
-1. One immutable collection of shades: `ImmutableShades`
-2. One mutable collection: `ShadesStack`
+1. One immutable collection of shades: `ImmutableShades` (readonly type)
+2. One mutable collection: `ShadeStack` (observable collection type)
 
 Use the first one if the shade collection will not change and the second one if you want to dynamically add or remove shades.
 
@@ -297,7 +352,7 @@ It will remove some xaml elements:
 
 ## Performance
 
-* On `Android`, shadows are created thanks to `RenderScript`. Bitmaps are cached and only recreated when needed
+* On `Android`, shadows are created thanks to `RenderScript`. Bitmaps are cached in a global `BitmapCache`. For a particular color, size and blur, you will only have one instance alive.
 * On `iOS`, a `Shade` is implemented with a simple `CALayer`
 * On `UWP`, `Shade` is implemented with `SpriteVisual` drop shadows.
 * On `Tizen`, `Shade` is implemented with `SkiaSharp`.

Sample/ShadowsSample.Android/CollectionViewLeakRenderer.cs

@@ -1,19 +1,8 @@
-using System;
-using System.Collections.Generic;
-using System.Linq;
-using System.Text;
-
-using Android.App;
-using Android.Content;
-using Android.OS;
-using Android.Runtime;
-using Android.Views;
-using Android.Widget;
+using Android.Content;
 
 using ShadowsSample.Droid;
 
 using Sharpnado.Presentation.Forms.Droid.Helpers;
-using Sharpnado.Shades.Droid;
 
 using Xamarin.Forms;
 using Xamarin.Forms.Platform.Android;
@@ -29,24 +18,26 @@ public CollectionViewLeakRenderer(Context context)
         {
         }
 
-        protected override void Dispose(bool disposing)
-        {
-            System.Diagnostics.Debug.WriteLine(ItemsViewAdapter);
+        //protected override void Dispose(bool disposing)
+        //{
+        //    System.Diagnostics.Debug.WriteLine(ItemsViewAdapter);
 
-            if (!disposing)
-            {
-                base.Dispose(false);
-                return;
-            }
+        //    if (!disposing)
+        //    {
+        //        base.Dispose(false);
+        //        return;
+        //    }
 
-            var children = GetChildren();
-            base.Dispose(true);
-            DisposeChildren(children);
-        }
+        //    var children = GetChildren();
+        //    base.Dispose(true);
+        //    DisposeChildren(children);
+        //}
 
         private ItemContentView[] GetChildren()
         {
             System.Diagnostics.Debug.WriteLine($"GetChildren() => count: {ChildCount}");
+
+            
             var result = new ItemContentView[ChildCount];
             for (int childCount = ChildCount, i = 0; i < childCount; ++i)
             {

Sample/ShadowsSample.Android/MainActivity.cs

@@ -34,15 +34,15 @@ protected override void OnCreate(Bundle savedInstanceState)
 
             LoadApplication(new App());
 
-            TaskMonitor.Create(
-                async () =>
-                    {
-                        while (true)
-                        {
-                            BitmapCache.Instance?.Log();
-                            await Task.Delay(10000);
-                        }
-                    });
+            //TaskMonitor.Create(
+            //    async () =>
+            //        {
+            //            while (true)
+            //            {
+            //                BitmapCache.Instance?.Log();
+            //                await Task.Delay(10000);
+            //            }
+            //        });
         }
 
         public override void OnRequestPermissionsResult(int requestCode, string[] permissions, [GeneratedEnum] Android.Content.PM.Permission[] grantResults)

Sample/ShadowsSample.Android/ShadowsSample.Android.csproj

@@ -33,6 +33,11 @@
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
     <AndroidLinkMode>None</AndroidLinkMode>
+    <AotAssemblies>false</AotAssemblies>
+    <EnableLLVM>false</EnableLLVM>
+    <AndroidEnableProfiledAot>false</AndroidEnableProfiledAot>
+    <BundleAssemblies>false</BundleAssemblies>
+    <EmbedAssembliesIntoApk>true</EmbedAssembliesIntoApk>
   </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Release|AnyCPU' ">
     <DebugSymbols>true</DebugSymbols>

Sample/ShadowsSample.sln

@@ -25,6 +25,7 @@ Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Nuget", "Nuget", "{3D7E0A15
 	ProjectSection(SolutionItems) = preProject
 		..\Shadows\AssemblyInfo.targets = ..\Shadows\AssemblyInfo.targets
 		..\make-package.ps1 = ..\make-package.ps1
+		..\README.md = ..\README.md
 		..\Sharpnado.Shadows.nuspec = ..\Sharpnado.Shadows.nuspec
 	EndProjectSection
 EndProject

Sample/ShadowsSample/App.xaml.cs

@@ -17,7 +17,7 @@ public App()
                 MainPage = new NavigationPage(new MainPage());
             }
 
-            Sharpnado.Shades.Initializer.Initialize(true, true, filter: "Renderer");
+            Sharpnado.Shades.Initializer.Initialize(true, true, filter: "ShadowsRenderer");
 
         }
 

Sample/ShadowsSample/ListItemCustomEasing.xaml

@@ -4,8 +4,7 @@
              xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
              xmlns:effects="clr-namespace:Sharpnado.Presentation.Forms.Effects;assembly=Sharpnado.Presentation.Forms"
              xmlns:images="clr-namespace:ShadowsSample.Images;assembly=ShadowsSample"
-             xmlns:materialFrame="clr-namespace:Sharpnado.MaterialFrame;assembly=Sharpnado.MaterialFrame"
-             xmlns:shades="clr-namespace:Sharpnado.Shades;assembly=Sharpnado.Shadows">
+             xmlns:materialFrame="clr-namespace:Sharpnado.MaterialFrame;assembly=Sharpnado.MaterialFrame">
 
     <!--<shades:Shadows.Shades>
         <shades:ImmutableShades>

Sample/ShadowsSample/MainPage.xaml

@@ -5,7 +5,7 @@
              xmlns:d="http://xamarin.com/schemas/2014/forms/design"
              xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
              mc:Ignorable="d"
-             xmlns:shades="clr-namespace:Sharpnado.Shades;assembly=Sharpnado.Shadows"
+             xmlns:sho="http://sharpnado.com"
              xmlns:views="clr-namespace:ShadowsSample.Views;assembly=ShadowsSample"
              BackgroundColor="{DynamicResource DynamicBackgroundColor}"
              BackgroundImageSource="{DynamicResource DynamicBackgroundImageSource}">
@@ -25,24 +25,29 @@
             <views:Logo HeightRequest="80"
                         Margin="0,0,0,10"
                         HorizontalOptions="Center"
-                        VerticalOptions="Center" />
+                        VerticalOptions="Center">
+                <views:Logo.GestureRecognizers>
+                    <TapGestureRecognizer Tapped="LogoOnTapped" />
+                </views:Logo.GestureRecognizers>
+            </views:Logo>
 
             <Label Style="{StaticResource TextBodySecondary}"
                    Margin="0,0,0,10"
                    HorizontalOptions="End"
                    FontFamily="{StaticResource FontItalic}"
                    Text="The above logo is made of 7 different shades." />
 
-            <shades:Shadows CornerRadius="10" Shades="{shades:NeumorphismShades}">
+            <sho:Shadows CornerRadius="10" Shades="{sho:NeumorphismShades}">
                 <Button Style="{StaticResource TextHeadline}"
+                        Padding="10"
                         HorizontalOptions="Center"
                         VerticalOptions="Center"
                         BackgroundColor="{DynamicResource DynamicFrameBackgroundColor}"
                         Clicked="OnNavigateToShadowsListClicked"
                         CornerRadius="10"
                         Text="Navigate to List of Shadows"
                         TextColor="Gray" />
-            </shades:Shadows>
+            </sho:Shadows>
 
             <Label Style="{StaticResource TextHeadline}"
                    Margin="{StaticResource HeaderMargin}"

Sample/ShadowsSample/MainPage.xaml.cs

@@ -1,5 +1,6 @@
 using System;
 using System.ComponentModel;
+using System.Threading.Tasks;
 
 using Sharpnado.Tasks;
 
@@ -24,11 +25,33 @@ protected override void OnAppearing()
         {
             base.OnAppearing();
             BeCreative.OnAppearing();
+
+            Device.BeginInvokeOnMainThread(async () =>
+                {
+                    GC.Collect();
+                    GC.WaitForPendingFinalizers();
+                    GC.Collect();
+                    GC.WaitForPendingFinalizers();
+                    GC.Collect();
+                    GC.WaitForPendingFinalizers();
+                    await Task.Delay(500);
+                    GC.Collect();
+                    GC.WaitForPendingFinalizers();
+                    GC.Collect();
+                    GC.WaitForPendingFinalizers();
+                    GC.Collect();
+                    GC.WaitForPendingFinalizers();
+                });
         }
 
         private void OnNavigateToShadowsListClicked(object sender, EventArgs e)
         {
             Navigation.PushAsync(new ShadowList());
         }
+
+        private void LogoOnTapped(object sender, EventArgs e)
+        {
+            Navigation.PopAsync();
+        }
     }
 }