Now lazy views activation is lifecycle aware (OnAppearing/OnDisappear…

…ing)

Nuget/Prism.Forms.LazyView.nuspec

@@ -2,7 +2,7 @@
 <package xmlns="http://schemas.microsoft.com/packaging/2011/08/nuspec.xsd">
   <metadata>
     <id>Prism.Forms.LazyView</id>
-    <version>1.2.0</version>
+    <version>1.3.0</version>
     <title>Prism.Forms.LazyView</title>
     <authors>Respawnsive,Jeremy Brun-Picard,Andrei Nitescu</authors>
     <owners>Respawnsive</owners>

Prism.Forms.LazyView/Behaviors/LazyLoadBehaviorBase.cs

@@ -54,6 +54,6 @@ void OnIsActiveChanged(object sender, EventArgs e)
             }
         }
 
-        protected abstract void SetContent(TVisualElement element, View contentView);
+        protected abstract void SetContent(TVisualElement element, View view);
     }
 }

Prism.Forms.LazyView/Behaviors/LazyLoadContentPageBehavior.cs

@@ -4,9 +4,9 @@ namespace Prism.Forms.LazyView.Behaviors
 {
     public class LazyLoadContentPageBehavior : LazyLoadBehaviorBase<ContentPage>
     {
-        protected override void SetContent(ContentPage page, View contentView)
+        protected override void SetContent(ContentPage contentPage, View view)
         {
-            page.Content = contentView;
+            contentPage.Content = view;
         }
     }
 }

Prism.Forms.LazyView/Behaviors/LazyLoadContentViewBehavior.cs

@@ -1,12 +1,14 @@
-using Xamarin.Forms;
+using Prism.AppModel;
+using Xamarin.Forms;
 
 namespace Prism.Forms.LazyView.Behaviors
 {
     public class LazyLoadContentViewBehavior : LazyLoadBehaviorBase<ContentView>
     {
-        protected override void SetContent(ContentView element, View contentView)
+        protected override void SetContent(ContentView contentView, View view)
         {
-            element.Content = contentView;
+            ((view as ContentView)?.BindingContext as IPageLifecycleAware)?.OnAppearing();
+            contentView.Content = view;
         }
     }
 }

Prism.Forms.LazyView/LazyContentView.cs

@@ -1,4 +1,5 @@
 using System;
+using Prism.AppModel;
 using Prism.Forms.LazyView.Behaviors;
 using Xamarin.Forms;
 
@@ -25,10 +26,22 @@ public bool IsActive
                 if (_isActive != value)
                 {
                     _isActive = value;
-                    IsActiveChanged?.Invoke(this, EventArgs.Empty);
+                    OnActivationChanged();
                 }
             }
         }
+
+        private void OnActivationChanged()
+        {
+            var isActiveChanged = IsActiveChanged;
+            if(isActiveChanged != null)
+                isActiveChanged.Invoke(this, EventArgs.Empty);
+            else if(Content is ContentView contentView && contentView.BindingContext is IPageLifecycleAware bindingContext)
+                if(_isActive)
+                    bindingContext.OnAppearing();
+                else
+                    bindingContext.OnDisappearing();
+        }
     }
 
     public class LazyContentView<TLoadingView, TContentView> : ContentView, IActiveAware where TLoadingView : View where TContentView : View
@@ -53,9 +66,21 @@ public bool IsActive
                 if (_isActive != value)
                 {
                     _isActive = value;
-                    IsActiveChanged?.Invoke(this, EventArgs.Empty);
+                    OnActivationChanged();
                 }
             }
         }
+
+        private void OnActivationChanged()
+        {
+            var isActiveChanged = IsActiveChanged;
+            if (isActiveChanged != null)
+                isActiveChanged.Invoke(this, EventArgs.Empty);
+            else if (Content is ContentView contentView && contentView.BindingContext is IPageLifecycleAware bindingContext)
+                if (_isActive)
+                    bindingContext.OnAppearing();
+                else
+                    bindingContext.OnDisappearing();
+        }
     }
 }

README.md

@@ -6,7 +6,9 @@ The original code has been adapted to Prism and published on Nuget.
 
 ### How to use it?
 
-Install the Prism.Forms.LazyView nuget package and on a TabbedPage (e.g.):
+Install the Prism.Forms.LazyView nuget package: [![NuGet](https://img.shields.io/nuget/v/Prism.Forms.LazyView.svg)](https://www.nuget.org/packages/Prism.Forms.LazyView/)
+
+Then for example on a TabbedPage:
 
 * Add some references:
 
@@ -33,6 +35,8 @@ YOUR_CONTENT_VIEW should be a Xamarin.Forms ContentView and will be created once
 
 YOUR_LOADING_VIEW should be a Xamarin.Forms ContentView and will be displayed while lazy loading YOUR_CONTENT_VIEW in a background thread
 
-Actually, it should work with any Prism control implementing MultiPageActiveAwareBehavior (e.g. Tabbed and Carousel)
+Actually, it should work with any Prism control implementing MultiPageActiveAwareBehavior (e.g. Tabbed and Carousel), but you can make it work from anywhere you're able to toggle the IsActive property (see "EncrustedSlowContentView").
+
+Now toggling IsActive on view side call OnAppearing/OnDisappearing on viewmodel side.
 
 More details on Sample project

Sample/Prism.Forms.LazyView.Sample/Prism.Forms.LazyView.Sample.csproj

@@ -20,6 +20,9 @@
   </ItemGroup>
 
   <ItemGroup>
+    <Compile Update="Views\EncrustedSlowContentView.xaml.cs">
+      <DependentUpon>EncrustedSlowContentView.xaml</DependentUpon>
+    </Compile>
     <Compile Update="Views\TabHostPage.xaml.cs">
       <DependentUpon>TabHostPage.xaml</DependentUpon>
     </Compile>
@@ -32,6 +35,9 @@
   </ItemGroup>
 
   <ItemGroup>
+    <EmbeddedResource Update="Views\EncrustedSlowContentView.xaml">
+      <Generator>MSBuild:UpdateDesignTimeXaml</Generator>
+    </EmbeddedResource>
     <EmbeddedResource Update="Views\LoadingSlowContentView.xaml">
       <Generator>MSBuild:UpdateDesignTimeXaml</Generator>
     </EmbeddedResource>

Sample/Prism.Forms.LazyView.Sample/ViewModels/EncrustedSlowContentViewModel.cs

@@ -0,0 +1,21 @@
+using Prism.Navigation;
+
+namespace Prism.Forms.LazyView.Sample.ViewModels
+{
+    public class EncrustedSlowContentViewModel : SlowContentViewModel
+    {
+        public EncrustedSlowContentViewModel(INavigationService navigationService) : base(navigationService)
+        {
+        }
+
+        public override void OnAppearing()
+        {
+            base.OnAppearing();
+        }
+
+        public override void OnDisappearing()
+        {
+            base.OnDisappearing();
+        }
+    }
+}

Sample/Prism.Forms.LazyView.Sample/Views/EncrustedSlowContentView.xaml

@@ -0,0 +1,15 @@
+<?xml version="1.0" encoding="UTF-8" ?>
+<ContentView
+    x:Class="Prism.Forms.LazyView.Sample.Views.EncrustedSlowContentView"
+    xmlns="http://xamarin.com/schemas/2014/forms"
+    xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+    xmlns:prism="http://prismlibrary.com"
+    xmlns:viewModels="clr-namespace:Prism.Forms.LazyView.Sample.ViewModels;assembly=Prism.Forms.LazyView.Sample"
+    prism:ViewModelLocator.AutowireViewModel="True"
+    x:DataType="viewModels:EncrustedSlowContentViewModel">
+    <ContentView.Content>
+        <StackLayout>
+            <Label Text="This should call the vm OnAppearing/OnDisappearing methods, when toggling IsActive" />
+        </StackLayout>
+    </ContentView.Content>
+</ContentView>

Sample/Prism.Forms.LazyView.Sample/Views/EncrustedSlowContentView.xaml.cs

@@ -0,0 +1,24 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+using Xamarin.Forms;
+using Xamarin.Forms.Xaml;
+
+namespace Prism.Forms.LazyView.Sample.Views
+{
+    [XamlCompilation(XamlCompilationOptions.Compile)]
+    public partial class EncrustedSlowContentView : ContentView
+    {
+        public EncrustedSlowContentView()
+        {
+            InitializeComponent();
+
+            // Simulating a complex view
+            // NEVER do this in real code
+            Task.Delay(TimeSpan.FromSeconds(3)).Wait();
+        }
+    }
+}

Sample/Prism.Forms.LazyView.Sample/Views/LoadingSlowContentView.xaml

@@ -1,16 +1,17 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<ContentView xmlns="http://xamarin.com/schemas/2014/forms" 
-             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
-             xmlns:d="http://xamarin.com/schemas/2014/forms/design"
-             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
-             mc:Ignorable="d"
-             x:Class="Prism.Forms.LazyView.Sample.Views.LoadingSlowContentView">
-  <ContentView.Content>
+<?xml version="1.0" encoding="UTF-8" ?>
+<ContentView
+    x:Class="Prism.Forms.LazyView.Sample.Views.LoadingSlowContentView"
+    xmlns="http://xamarin.com/schemas/2014/forms"
+    xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+    xmlns:d="http://xamarin.com/schemas/2014/forms/design"
+    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+    mc:Ignorable="d">
+    <ContentView.Content>
         <Grid>
-            <StackLayout VerticalOptions="Center" HorizontalOptions="Center">
-                <ActivityIndicator IsRunning="True" HorizontalOptions="Center"/>
-                <Label Text="{Binding Counter, StringFormat='Loading View and ViewModel...{0}0%'}" HorizontalOptions="Center"/>
+            <StackLayout HorizontalOptions="Center" VerticalOptions="Center">
+                <ActivityIndicator HorizontalOptions="Center" IsRunning="True" />
+                <Label HorizontalOptions="Center" Text="{Binding Counter, StringFormat='Loading View and ViewModel...{0}0%'}" />
             </StackLayout>
         </Grid>
-  </ContentView.Content>
+    </ContentView.Content>
 </ContentView>

Sample/Prism.Forms.LazyView.Sample/Views/SlowContentView.xaml

@@ -1,34 +1,54 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<ContentView xmlns="http://xamarin.com/schemas/2014/forms" 
-             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
-             xmlns:viewModels="clr-namespace:Prism.Forms.LazyView.Sample.ViewModels;assembly=Prism.Forms.LazyView.Sample"
-             x:Class="Prism.Forms.LazyView.Sample.Views.SlowContentView" 
-             Margin="10"
-             x:DataType="viewModels:SlowContentViewModel">
+<?xml version="1.0" encoding="UTF-8" ?>
+<ContentView
+    x:Class="Prism.Forms.LazyView.Sample.Views.SlowContentView"
+    xmlns="http://xamarin.com/schemas/2014/forms"
+    xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+    xmlns:lazyView="clr-namespace:Prism.Forms.LazyView;assembly=Prism.Forms.LazyView"
+    xmlns:viewModels="clr-namespace:Prism.Forms.LazyView.Sample.ViewModels;assembly=Prism.Forms.LazyView.Sample"
+    xmlns:views="clr-namespace:Prism.Forms.LazyView.Sample.Views;assembly=Prism.Forms.LazyView.Sample"
+    Margin="10"
+    x:DataType="viewModels:SlowContentViewModel">
     <Grid>
-        <StackLayout Orientation="Vertical" HorizontalOptions="Center" VerticalOptions="Center">
-            <Label Text="{Binding Description}"
-                   HorizontalOptions="Center" LineBreakMode="WordWrap" />
+        <StackLayout
+            HorizontalOptions="Center"
+            Orientation="Vertical"
+            VerticalOptions="Center">
+            <Label
+                HorizontalOptions="Center"
+                LineBreakMode="WordWrap"
+                Text="{Binding Description}" />
             <StackLayout Orientation="Horizontal">
-                <Label Text="Long process on ViewModel:"/>
-                <Label Text="{Binding Counter, StringFormat='{0}0%'}"
-                       HorizontalOptions="Center">
+                <Label Text="Long process on ViewModel:" />
+                <Label HorizontalOptions="Center" Text="{Binding Counter, StringFormat='{0}0%'}">
                     <Label.Triggers>
-                        <DataTrigger TargetType="Label" Binding="{Binding Counter}" Value="0">
-                            <Setter Property="IsVisible" Value="False"/>
+                        <DataTrigger
+                            Binding="{Binding Counter}"
+                            TargetType="Label"
+                            Value="0">
+                            <Setter Property="IsVisible" Value="False" />
                         </DataTrigger>
                     </Label.Triggers>
                 </Label>
-                <Label Text="Result!"
-                       HorizontalOptions="Center" IsVisible="False">
+                <Label
+                    HorizontalOptions="Center"
+                    IsVisible="False"
+                    Text="Result!">
                     <Label.Triggers>
-                        <DataTrigger TargetType="Label" Binding="{Binding Counter}" Value="0">
-                            <Setter Property="IsVisible" Value="True"/>
+                        <DataTrigger
+                            Binding="{Binding Counter}"
+                            TargetType="Label"
+                            Value="0">
+                            <Setter Property="IsVisible" Value="True" />
                         </DataTrigger>
                     </Label.Triggers>
                 </Label>
             </StackLayout>
-            <Button Text="Navigate to Other" Command="{Binding NavigateCommand}"/>
+            <Button Command="{Binding NavigateCommand}" Text="Navigate to Other" />
+            <Button Clicked="Button_OnClicked" Text="Toggle incrusted view" />
+            <lazyView:LazyContentView
+                x:Name="LazyContentView"
+                x:DataType="viewModels:EncrustedSlowContentViewModel"
+                x:TypeArguments="views:LoadingSlowContentView,views:EncrustedSlowContentView" />
         </StackLayout>
     </Grid>
 </ContentView>

Sample/Prism.Forms.LazyView.Sample/Views/SlowContentView.xaml.cs

@@ -14,5 +14,10 @@ public SlowContentView()
             // NEVER do this in real code
             Task.Delay(TimeSpan.FromSeconds(3)).Wait();
         }
+
+        private void Button_OnClicked(object sender, EventArgs e)
+        {
+            LazyContentView.IsActive = !LazyContentView.IsActive;
+        }
     }
 }

Sample/Prism.Forms.LazyView.Sample/Views/TabHostPage.xaml

@@ -1,40 +1,29 @@
 <?xml version="1.0" encoding="utf-8" ?>
-<TabbedPage xmlns="http://xamarin.com/schemas/2014/forms"
-             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
-             xmlns:prism="http://prismlibrary.com"
-             prism:ViewModelLocator.AutowireViewModel="True"
-             xmlns:android="clr-namespace:Xamarin.Forms.PlatformConfiguration.AndroidSpecific;assembly=Xamarin.Forms.Core"
-             android:TabbedPage.ToolbarPlacement="Bottom"
-             xmlns:views="clr-namespace:Prism.Forms.LazyView.Sample.Views;assembly=Prism.Forms.LazyView.Sample"
-             xmlns:lazyView="clr-namespace:Prism.Forms.LazyView;assembly=Prism.Forms.LazyView"
-             xmlns:behaviors="clr-namespace:Prism.Forms.LazyView.Behaviors;assembly=Prism.Forms.LazyView"
-             x:Class="Prism.Forms.LazyView.Sample.Views.TabHostPage"
-             xmlns:viewModels="clr-namespace:Prism.Forms.LazyView.Sample.ViewModels;assembly=Prism.Forms.LazyView.Sample"
-             x:Name="This"
-             Title="{Binding Title}" 
-             BarBackgroundColor="LightGray">
+<TabbedPage
+    x:Class="Prism.Forms.LazyView.Sample.Views.TabHostPage"
+    xmlns="http://xamarin.com/schemas/2014/forms"
+    xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+    xmlns:android="clr-namespace:Xamarin.Forms.PlatformConfiguration.AndroidSpecific;assembly=Xamarin.Forms.Core"
+    xmlns:behaviors="clr-namespace:Prism.Forms.LazyView.Behaviors;assembly=Prism.Forms.LazyView"
+    xmlns:lazyView="clr-namespace:Prism.Forms.LazyView;assembly=Prism.Forms.LazyView"
+    xmlns:prism="http://prismlibrary.com"
+    xmlns:viewModels="clr-namespace:Prism.Forms.LazyView.Sample.ViewModels;assembly=Prism.Forms.LazyView.Sample"
+    xmlns:views="clr-namespace:Prism.Forms.LazyView.Sample.Views;assembly=Prism.Forms.LazyView.Sample"
+    x:Name="This"
+    Title="{Binding Title}"
+    android:TabbedPage.ToolbarPlacement="Bottom"
+    prism:ViewModelLocator.AutowireViewModel="True"
+    BarBackgroundColor="LightGray">
 
-    <!--A page defined from here-->
-    <ContentPage Title="Builtin">
-        <Grid>
-            <StackLayout Orientation="Vertical"
-                         HorizontalOptions="Center" 
-                         VerticalOptions="Center">
-                <Label Text="A page defined from the TabHostPage" />
-                <Button Text="Select Lazy tab" 
-                        Command="{prism:SelectTab SlowContentView}"/>
-            </StackLayout>
-        </Grid>
-    </ContentPage>
+    <!--  A normal page referenced  -->
+    <views:StandardPage />
 
-    <!--A normal page referenced-->
-    <!--<views:StandardPage/>-->
+    <views:TopTabHostPage />
 
-    <views:TopTabHostPage/>
-
-    <!--A page referenced but constructed the lazy way-->
-    <lazyView:LazyContentPage Title="{Binding Title}" 
-                              x:DataType="viewModels:SlowContentViewModel"
-                              x:TypeArguments="views:LoadingSlowContentView,views:SlowContentView"/>
+    <!--  A page referenced but constructed the lazy way  -->
+    <lazyView:LazyContentPage
+        Title="{Binding Title}"
+        x:DataType="viewModels:SlowContentViewModel"
+        x:TypeArguments="views:LoadingSlowContentView,views:SlowContentView" />
 
 </TabbedPage>