在 Xamarin Forms 中加载查看内容时显示活动指示器

有没有办法在页面内容视图渲染或加载时显示活动指示器？我问这个是因为当我在页面中有很多控件并且我想导航到该页面时，需要几秒钟的时间到页面。所以我想知道是否有一种方法可以即时导航页面，并且当页面出现时显示加载内容的活动指示器，以及当内容加载时显示它。

有没有办法在页面内容视图渲染或加载时显示活动指示器？

1. 我们需要在PCL中创建服务名称ILodingPageService接口。

    public interface ILodingPageService
     {
    void InitLoadingPage(ContentPage loadingIndicatorPage = null);
    void ShowLoadingPage();
    void HideLoadingPage();
   
     }
   

2. 创建透明页面以显示活动指示器。

    <ContentPage.Content>
        <StackLayout
            Padding="30"
            BackgroundColor="Black"
            HorizontalOptions="Center"
            VerticalOptions="Center">
   
            <ActivityIndicator IsRunning="True" Color="White" />
   
            <Label
                FontAttributes="Bold"
                Text="Loading..."
                TextColor="White" />
   
        </StackLayout>
    </ContentPage.Content>
   

3. 在Android平台上实现ILodingPageService接口。

    [assembly: Xamarin.Forms.Dependency(typeof(LodingPageServiceDroid))]
    namespace IndicatorApp.Droid
    {  
        public class LodingPageServiceDroid : ILodingPageService
        {
   
            private Android.Views.View _nativeView;
            private Dialog _dialog;
            private bool _isInitialized;
            public void HideLoadingPage()
            {
                // Hide the page
   
                _dialog.Hide();
            }
   
            public void InitLoadingPage(ContentPage loadingIndicatorPage = null)
            {
                // check if the page parameter is available
                if (loadingIndicatorPage != null)
                {
                    // build the loading page with native base
                    loadingIndicatorPage.Parent = Xamarin.Forms.Application.Current.MainPage;
                    loadingIndicatorPage.Layout(new Rectangle(0, 0,
                    Xamarin.Forms.Application.Current.MainPage.Width,
                    Xamarin.Forms.Application.Current.MainPage.Height));
                    var renderer = loadingIndicatorPage.GetOrCreateRenderer();
                    _nativeView = renderer.View;
                    _dialog = new Dialog(CrossCurrentActivity.Current.Activity);
   
                    _dialog.RequestWindowFeature((int)WindowFeatures.NoTitle);
   
                    _dialog.SetCancelable(false);
   
                    _dialog.SetContentView(_nativeView);
   
                    Window window = _dialog.Window;
   
                    window.SetLayout(ViewGroup.LayoutParams.MatchParent, ViewGroup.LayoutParams.MatchParent);
   
                    window.ClearFlags(WindowManagerFlags.DimBehind);
   
                    window.SetBackgroundDrawable(new ColorDrawable(Android.Graphics.Color.Transparent));
                    _isInitialized = true;
                }
            }
   
            public void ShowLoadingPage()
            {
                // check if the user has set the page or not
                if (!_isInitialized)
                    InitLoadingPage(new LoadingIndicatorPage1()); // set the default page
   
                // showing the native loading page
   
                _dialog.Show();
            }
        }
        internal static class PlatformExtension
        {
            public static IVisualElementRenderer GetOrCreateRenderer(this VisualElement bindable)
            {
                var renderer = XFPlatform.GetRenderer(bindable);
                if (renderer == null)
                {
                    renderer = XFPlatform.CreateRendererWithContext(bindable, CrossCurrentActivity.Current.Activity);
   
                    XFPlatform.SetRenderer(bindable, renderer);
   
                }
   
                return renderer;
   
            }
   
        }
    }
   

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