45、SplashScreen

     当应用程序加载时，如果耗费的事件比较长，可以自定义 SplashScreen ，来延长加载过程。

    系统的 SplashScreen 类：

namespace Windows.ApplicationModel.Activation
{
    
    // 为应用程序的初始屏幕提供关闭事件和屏幕位置信息。
    public sealed class SplashScreen
    {        
       // 相对于窗体的应用程序初始屏幕图像的坐标。
        // 返回结果: 相对于窗体并且针对设备的点/英寸 (dpi) 的初始屏幕图像的坐标。
        public Rect ImageLocation { get; }

       // 当关闭应用程序的初始屏幕时激发。
        public event TypedEventHandler<SplashScreen, object> Dismissed;
    }
}

  1、  App.xaml.cs 文件中的  protected override void OnLaunched(LaunchActivatedEventArgs args) 方法，形参 args 中包含默认

SplashScreen 的引用 ：args.SplashScreen。

首先自定义一个 “闪屏页面”（ ExtendedSplash ）：

XAML ：

<Grid Background="#00b2f0"
      x:Class="SplashScreenSample.ExtendedSplash"
      xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
      xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
      xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
      xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
      mc:Ignorable="d"
      d:DesignWidth="1366" d:DesignHeight="768">

    
    <Grid.RowDefinitions>
        <RowDefinition/>
        <RowDefinition Height="180"/>
    </Grid.RowDefinitions>

    <Canvas Grid.Row="0">
        <Image x:Name="extendedSplashImage" Source="Assets/splash-sdk.png" />
    </Canvas>
    <StackPanel Grid.Row="1" HorizontalAlignment="Center">
        <TextBlock Style="{StaticResource BasicTextStyle}" TextWrapping="Wrap" TextAlignment="Center" Padding="5" HorizontalAlignment="Center">
            The splash screen was dismissed and the image above was positioned using the splash screen API.
        </TextBlock>
        <Button x:Name="LearnMoreButton" Content="Learn More" HorizontalAlignment="Center" />
    </StackPanel>
</Grid>

相应的 C# 页面 ：

namespace SplashScreenSample
{
    partial class ExtendedSplash
    {

        //存储应用默认 “闪屏” 的位置
        internal Rect splashImageRect;

        //跟踪闪屏的消失状态
         internal bool dismissed = false; 
        internal Frame rootFrame;

       //引用到应用默认的闪屏对象
        private SplashScreen splash; 

        public ExtendedSplash(SplashScreen splashscreen, bool loadState)
        {
            InitializeComponent();

            LearnMoreButton.Click += new RoutedEventHandler(LearnMoreButton_Click);
            // 侦听窗口尺寸改变事件，从而重置闪屏图片的位置
              Window.Current.SizeChanged += new WindowSizeChangedEventHandler(ExtendedSplash_OnResize);

            splash = splashscreen;

            if (splash != null)
            {
                //  当关闭应用程序的初始屏幕时激发。
                splash.Dismissed += new TypedEventHandler<SplashScreen, Object>(DismissedEventHandler);

               
             //获取闪屏的默认图片
                splashImageRect = splash.ImageLocation;
              PositionImage();
            }
    
          //初始化一个 Frame 对象，作为默认导航的上下文
            rootFrame = new Frame();
            
          //需要时，恢复保存的会话状态
            RestoreStateAsync(loadState);
            
        }

        async void RestoreStateAsync(bool loadState)
        {
            if (loadState)
                await SuspensionManager.RestoreAsync();
               

        }

        // 把扩展的闪屏图片放在默认闪屏图片的位置
         void PositionImage()
        {
            extendedSplashImage.SetValue(Canvas.LeftProperty, splashImageRect.X);
            extendedSplashImage.SetValue(Canvas.TopProperty, splashImageRect.Y);
            extendedSplashImage.Height = splashImageRect.Height;
            extendedSplashImage.Width = splashImageRect.Width;
        }

        void ExtendedSplash_OnResize(Object sender, WindowSizeChangedEventArgs e)
        {
              if (splash != null)
            {
                 splashImageRect = splash.ImageLocation;
                PositionImage();
            }
        }

        void LearnMoreButton_Click(object sender, RoutedEventArgs e)
        {
            // 当点击按钮后，导航到 MainPage
            rootFrame.Navigate(typeof(MainPage));

            //把 extended splash  对象保存到 MainPage 中的引用
             ((MainPage)rootFrame.Content).SetExtendedSplashInfo(splashImageRect, dismissed);

            Window.Current.Content = rootFrame;
            
        }

        // 当系统闪屏消失，导航到当前闪屏时触发
         void DismissedEventHandler(SplashScreen sender, object e)
        {
            dismissed = true;  
        }
    }
}

  在 App.xaml.cs 文件中的  OnLaunched() 方法中，初始化并显示闪屏：

 protected override void OnLaunched(LaunchActivatedEventArgs args)
 {
     if (args.PreviousExecutionState != ApplicationExecutionState.Running)
     {
         bool loadState = (args.PreviousExecutionState == ApplicationExecutionState.Terminated);
         ExtendedSplash extendedSplash = new ExtendedSplash(args.SplashScreen, loadState);
         Window.Current.Content = extendedSplash;
     }
     
     Window.Current.Activate();
 }

2、获取闪屏图像的坐标。

显示结果的 XAML ：

 <TextBlock Style="{StaticResource BasicTextStyle}" TextWrapping="Wrap">
     The splash screen was positioned at
     <Run FontWeight="Bold" Text="x:"/><Run x:Name="XValue"/>
     <Run FontWeight="Bold" Text="y:"/><Run x:Name="YValue"/>
     <Run FontWeight="Bold" Text=""/><Run x:Name="WidthValue"/>
     <Run FontWeight="Bold" Text="height:"/><Run x:Name="HeightValue"/>
 </TextBlock>

相应的 C# ：

 protected override void OnNavigatedTo(NavigationEventArgs e)
 {
     //在 MainPage 页面中，保存系统的 SplashScreen 位置的引用
      Rect rect = MainPage.Current.SplashImageRect;
     XValue.Text = " " + rect.X.ToString() + ", ";
     YValue.Text = " " + rect.Y.ToString() + " with ";
     WidthValue.Text = " " + rect.Width.ToString() + ", ";
     HeightValue.Text = " " + rect.Height.ToString() + ".";
 }