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pictospictos
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Implemented LazyView (#796)
* Created LazyView and implemented it on TabView * Added Preserve attribute * Update LazyTestView.xaml
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‎samples/XCT.Sample/Pages/Views/TabView/LazyTabPage.xaml

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<?xml version="1.0" encoding="utf-8" ?>
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<pages:BasePage
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x:Class="Xamarin.CommunityToolkit.Sample.Pages.Views.TabView.LazyTabPage"
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xmlns="http://xamarin.com/schemas/2014/forms"
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xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
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xmlns:local="clr-namespace:Xamarin.CommunityToolkit.Sample.Pages.Views.TabView"
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xmlns:pages="clr-namespace:Xamarin.CommunityToolkit.Sample.Pages"
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xmlns:vm="clr-namespace:Xamarin.CommunityToolkit.Sample.ViewModels.Views.Tabs"
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xmlns:xct="http://xamarin.com/schemas/2020/toolkit">
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<pages:BasePage.Content>
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<Grid>
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<xct:TabView
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TabContentBackgroundColor="Yellow"
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TabIndicatorColor="Yellow"
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TabStripBackgroundColor="Blue"
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TabStripHeight="60"
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TabStripPlacement="Bottom">
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<xct:TabViewItem
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FontSize="12"
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Icon="triangle.png"
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Text="Tab Normal 1"
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TextColor="White"
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TextColorSelected="Yellow">
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<local:NormalTestView />
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</xct:TabViewItem>
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<xct:TabViewItem
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FontSize="12"
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Icon="circle.png"
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Text="Tab Lazy 2"
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TextColor="White"
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TextColorSelected="Yellow">
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<xct:LazyView
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x:TypeArguments="local:LazyTestView"
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BindingContext="{x:Static vm:LazyTestViewModel.Current}"
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IsLoaded="{Binding Loaded}" />
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</xct:TabViewItem>
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<xct:TabViewItem
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FontSize="12"
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Icon="triangle.png"
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Text="Tab Normal 3"
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TextColor="White"
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TextColorSelected="Yellow">
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<local:NormalTestView />
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</xct:TabViewItem>
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<xct:TabViewItem
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FontSize="12"
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Icon="triangle.png"
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Text="Tab Lazy 4"
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TextColor="White"
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TextColorSelected="Yellow">
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<xct:LazyView x:TypeArguments="local:LazyTestView" BindingContext="{x:Static vm:LazyTestViewModel.Current}" />
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</xct:TabViewItem>
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</xct:TabView>
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</Grid>
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</pages:BasePage.Content>
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</pages:BasePage>

‎samples/XCT.Sample/Pages/Views/TabView/LazyTabPage.xaml.cs

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namespace Xamarin.CommunityToolkit.Sample.Pages.Views.TabView
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{
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public partial class LazyTabPage
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{
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public LazyTabPage() => InitializeComponent();
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}
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}

‎samples/XCT.Sample/Pages/Views/TabView/LazyTestView.xaml

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<?xml version="1.0" encoding="UTF-8" ?>
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<ContentView
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x:Class="Xamarin.CommunityToolkit.Sample.Pages.Views.TabView.LazyTestView"
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xmlns="http://xamarin.com/schemas/2014/forms"
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xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
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xmlns:xct="http://xamarin.com/schemas/2020/toolkit">
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<ContentView.Content>
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<Grid RowDefinitions="auto, *">
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<Label
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FontSize="Title"
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HorizontalTextAlignment="Center"
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Text="{Binding Title}"
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TextColor="Black" />
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<xct:UniformGrid x:Name="uniformGrid" Grid.Row="1" />
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</Grid>
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</ContentView.Content>
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</ContentView>

‎samples/XCT.Sample/Pages/Views/TabView/LazyTestView.xaml.cs

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using Xamarin.CommunityToolkit.Sample.ViewModels.Views.Tabs;
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using Xamarin.Forms;
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namespace Xamarin.CommunityToolkit.Sample.Pages.Views.TabView
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{
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public partial class LazyTestView : ContentView
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{
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public LazyTestView()
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{
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InitializeComponent();
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Build();
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NormalTestViewModel.Current.LoadedViews += "LazyView Loaded \n";
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}
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void Build()
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{
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for (var i = 0; i < 117; i++)
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{
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var box = new BoxView
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{
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BackgroundColor = i % 2 == 0 ? Color.Blue : Color.Fuchsia
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};
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uniformGrid.Children.Add(box);
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}
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}
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}
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}

‎samples/XCT.Sample/Pages/Views/TabView/NormalTestView.xaml

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<?xml version="1.0" encoding="UTF-8" ?>
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<ContentView
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x:Class="Xamarin.CommunityToolkit.Sample.Pages.Views.TabView.NormalTestView"
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xmlns="http://xamarin.com/schemas/2014/forms"
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xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml">
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<ContentView.Content>
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<StackLayout>
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<Label Text="{Binding LoadedViews}" />
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</StackLayout>
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</ContentView.Content>
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</ContentView>

‎samples/XCT.Sample/Pages/Views/TabView/NormalTestView.xaml.cs

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using Xamarin.CommunityToolkit.Sample.ViewModels.Views.Tabs;
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using Xamarin.Forms;
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namespace Xamarin.CommunityToolkit.Sample.Pages.Views.TabView
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{
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public partial class NormalTestView : ContentView
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{
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public NormalTestView()
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{
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InitializeComponent();
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BindingContext = NormalTestViewModel.Current;
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NormalTestViewModel.Current.LoadedViews += "NormalTestLoaded \n";
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}
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}
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}

‎samples/XCT.Sample/ViewModels/Views/TabViewViewModel.cs

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"Customize the tabs width"),
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new SectionModel(typeof(NoContentPage), "Tab without Content",
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"Only the TabStrip is visible")
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"Only the TabStrip is visible"),
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new SectionModel(typeof(LazyTabPage), "LazyLoadingTab",
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"See how you can implement LazyViews that are loaded just when you navigate to them"),
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};
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}
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}

‎samples/XCT.Sample/ViewModels/Views/Tabs/LazyTestViewModel.cs

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using Xamarin.CommunityToolkit.ObjectModel;
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namespace Xamarin.CommunityToolkit.Sample.ViewModels.Views.Tabs
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{
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sealed class LazyTestViewModel : ObservableObject
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{
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public static LazyTestViewModel Current { get; } = new LazyTestViewModel();
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string title;
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public string Title
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{
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get => title;
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set => SetProperty(ref title, value);
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}
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bool loaded;
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public bool Loaded
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{
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get => loaded;
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set => SetProperty(ref loaded, value);
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}
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public LazyTestViewModel() => Title = "Lazy Tab Sample";
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}
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}

‎samples/XCT.Sample/ViewModels/Views/Tabs/NormalTestViewModel.cs

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using Xamarin.CommunityToolkit.ObjectModel;
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namespace Xamarin.CommunityToolkit.Sample.ViewModels.Views.Tabs
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{
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sealed class NormalTestViewModel : ObservableObject
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{
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public static NormalTestViewModel Current { get; } = new NormalTestViewModel();
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string loadedViews;
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public string LoadedViews
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{
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get => loadedViews;
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set => SetProperty(ref loadedViews, value);
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}
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}
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}

‎src/CommunityToolkit/Xamarin.CommunityToolkit/Views/LazyView/BaseLazyView.shared.cs

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using System;
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using Xamarin.Forms;
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using Xamarin.Forms.Internals;
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namespace Xamarin.CommunityToolkit.UI.Views
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{
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[Preserve(Conditional =true)]
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public abstract class BaseLazyView : ContentView, IDisposable
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{
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internal static readonly BindablePropertyKey IsLoadedPropertyKey = BindableProperty.CreateReadOnly(nameof(IsLoaded), typeof(bool), typeof(BaseLazyView), default);
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public static readonly BindableProperty IsLoadedProperty = IsLoadedPropertyKey.BindableProperty;
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public bool IsLoaded => (bool)GetValue(IsLoadedProperty);
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internal void SetIsLoaded(bool isLoaded) => SetValue(IsLoadedPropertyKey, isLoaded);
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public abstract void LoadView();
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public void Dispose()
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{
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if (Content is IDisposable disposable)
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disposable.Dispose();
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}
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protected override void OnBindingContextChanged()
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{
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if (Content != null && !(Content is ActivityIndicator))
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Content.BindingContext = BindingContext;
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}
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}
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}

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