Windows 10 开发 - 服务

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本章将学习 UWP 应用如何帮助或提供服务给其他通用 Windows 平台 (UWP) 应用。实际上，本章是对后台执行章节的扩展，是其一个特例。

  • 在 Windows 10 中，应用服务是一种允许应用向其他应用提供服务的方式或机制。

  • 应用服务以后台任务的形式运行。

  • 前台应用可以调用另一个应用中的应用服务来执行后台任务。

APP Services

应用服务类似于 Web 服务，但应用服务用于 Windows 10 设备。

通用 Windows 平台 (UWP) 应用可以通过多种方式与其他 UWP 应用交互：

  • 使用 LaunchUriAsync 的 URI 关联
  • 使用 LaunchFileAsync 的文件关联
  • 使用 LaunchUriForResultsAsync 启动以获取结果
  • 应用服务

前三种方式用于两个应用都处于前台的情况，而应用服务则用于后台任务，在这种情况下，客户端应用必须处于前台并可用以使用应用服务。

应用服务在提供非可视化服务的应用中非常有用，例如条形码扫描器，其中前台应用将拍摄图像并将这些字节发送到应用服务以识别条形码。

为了理解所有这些概念，让我们在 Microsoft Visual Studio 2015 中创建一个名为AppServiceProvider 的新的 UWP 项目。

现在在Package.appmanifest 文件中，添加以下信息。

APP Services

要创建一个可以被前台应用程序调用的应用服务，让我们向解决方案添加一个新的Windows 运行时组件项目，命名为MyAppService，因为应用服务是作为后台任务实现的。

在AppServiceProvider 项目中添加对MyAppService 项目的引用。

现在从MyAppService 项目中删除class1.cs 文件，并添加一个具有清单名称的新类，该类将实现IBackgroundTask 接口。

IBackgroundTask 接口只有一个方法“Run”，需要为后台任务实现该方法。

public sealed class Inventory : IBackgroundTask { 
   public void Run(IBackgroundTaskInstance taskInstance) { 
      
   } 
}

创建后台任务时，将调用Run() 方法，当 Run 方法完成时，后台任务将终止。为了使后台任务保持活动状态以服务请求，代码会获取一个延迟对象。

应用服务的代码位于OnRequestedReceived() 中。在此示例中，库存项的索引传递给服务，以检索指定库存项的名称和价格。

private async void OnRequestReceived(AppServiceConnection sender, 
   AppServiceRequestReceivedEventArgs args) {
      // Get a deferral because we use an awaitable API below to respond to the message 
}

以下是 C# 中 Inventory 类的完整实现。

using System; 
using System.Collections.Generic; 
using System.Linq; 
using System.Text; 
using System.Threading.Tasks; 

using Windows.ApplicationModel.AppService; 
using Windows.ApplicationModel.Background; 
using Windows.Foundation.Collections;  

namespace MyAppService{
   public sealed class Inventory : IBackgroundTask { 
	
      private BackgroundTaskDeferral backgroundTaskDeferral; 
      private AppServiceConnection appServiceconnection; 
		
      private String[] inventoryItems = new string[] { "Robot vacuum", "Chair" }; 
      private double[] inventoryPrices = new double[] { 129.99, 88.99 };
		
      public void Run(IBackgroundTaskInstance taskInstance) {
         this.backgroundTaskDeferral = taskInstance.GetDeferral(); 
         taskInstance.Canceled += OnTaskCanceled;  
         var details = taskInstance.TriggerDetails as AppServiceTriggerDetails;
			
         appServiceconnection = details.AppServiceConnection;
         appServiceconnection.RequestReceived += OnRequestReceived; 
      } 
		
      private async void OnRequestReceived(AppServiceConnection sender,
         AppServiceRequestReceivedEventArgs args) {
        
            var messageDeferral = args.GetDeferral(); 
            ValueSet message = args.Request.Message; 
            ValueSet returnData = new ValueSet();  
				
            string command = message["Command"] as string; 
            int? inventoryIndex = message["ID"] as int?;  
            if (inventoryIndex.HasValue && 
				
            inventoryIndex.Value >= 0 && 
            inventoryIndex.Value < inventoryItems.GetLength(0)) {
		 
               switch (command) {
			
                  case "Price": {
                     returnData.Add("Result", inventoryPrices[inventoryIndex.Value]); 
                     returnData.Add("Status", "OK"); 
                     break; 
                  } 
					
                  case "Item": {
                     returnData.Add("Result", inventoryItems[inventoryIndex.Value]); 
                     returnData.Add("Status", "OK"); 
                     break; 
                  }  
					
                  default: {
                     returnData.Add("Status", "Fail: unknown command"); 
                     break; 
                  }
               } else {
                  returnData.Add("Status", "Fail: Index out of range"); 
               } 
            }			
            await args.Request.SendResponseAsync(returnData); 
            messageDeferral.Complete(); 
      } 
		
      private void OnTaskCanceled(IBackgroundTaskInstance sender,
         BackgroundTaskCancellationReason reason){ 
            if (this.backgroundTaskDeferral != null) {
               // Complete the service deferral. 
               this.backgroundTaskDeferral.Complete(); 
            } 
      } 
   } 
}

让我们通过添加一个新的空白 UWP 项目ClientApp 来创建一个客户端应用，并添加一个按钮、一个文本框和两个文本块，如下所示 XAML 文件。

<Page 
   x:Class = "ClientApp.MainPage" 
   xmlns = "http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
   xmlns:x = "http://schemas.microsoft.com/winfx/2006/xaml" 
   xmlns:local = "using:ClientApp" 
   xmlns:d = "http://schemas.microsoft.com/expression/blend/2008" 
   xmlns:mc = "http://schemas.openxmlformats.org/markup-compatibility/2006" 
   mc:Ignorable = "d"> 
   
   <Grid Background = "{ThemeResource ApplicationPageBackgroundThemeBrush}"> 
      <TextBlock HorizontalAlignment = "Left" Text = "Enter Item No." 
         Margin = "52,40,0,0" TextWrapping = "Wrap"
         VerticalAlignment = "Top" Height = "32" Width = "268"/> 
			
      <Button x:Name = "button" Content = "Get Info" HorizontalAlignment = "Left"  
         Margin = "255,96,0,0" VerticalAlignment = "Top" Click = "button_Click"/>
			
      <TextBox x:Name = "textBox" HorizontalAlignment = "Left" Margin = "52,96,0,0"  
         TextWrapping = "Wrap" VerticalAlignment = "Top" Width = "168"/>
			
      <TextBlock x:Name = "textBlock" HorizontalAlignment = "Left"  
         Margin = "52,190,0,0" TextWrapping = "Wrap"  
         VerticalAlignment = "Top" Height = "32" Width = "268"/> 
   </Grid> 
	
</Page>

以下是请求应用服务的按钮单击事件实现。

using System; 

using Windows.ApplicationModel.AppService; 
using Windows.Foundation.Collections;
 
using Windows.UI.Xaml; 
using Windows.UI.Xaml.Controls;
  
// The Blank Page item template is documented at 
   http://go.microsoft.com/fwlink/?LinkId=402352&clcid=0x409  

namespace ClientApp {

   /// <summary> 
      /// An empty page that can be used on its own or navigated to within a Frame. 
   /// </summary> 
	
   public sealed partial class MainPage : Page {
   
      private AppServiceConnection inventoryService; 
	  
      public MainPage() {
         this.InitializeComponent(); 
      } 
		
      private async void button_Click(object sender, RoutedEventArgs e){
	  
         // Add the connection. 
         if (this.inventoryService == null) {
		 
            this.inventoryService = new AppServiceConnection(); 
            this.inventoryService.AppServiceName = "com.microsoft.inventory"; 
            this.inventoryService.PackageFamilyName = 
               "bb1a8478-8005-46869923-e525ceaa26fc_4sz2ag3dcq60a"; 
					
            var status = await this.inventoryService.OpenAsync();
				
            if (status != AppServiceConnectionStatus.Success) {
               button.Content = "Failed to connect"; 
               return; 
            } 
         } 
			
         // Call the service. 
         int idx = int.Parse(textBox.Text); 
         var message = new ValueSet(); 
			
         message.Add("Command", "Item"); 
         message.Add("ID", idx); 
			
         AppServiceResponse response = await 
            this.inventoryService.SendMessageAsync(message); 
         string result = ""; 
			
         if (response.Status == AppServiceResponseStatus.Success) { 
            // Get the data  that the service sent  to us. 
            if (response.Message["Status"] as string == "OK") {
               result = response.Message["Result"] as string; 
            } 
         } 
			
         message.Clear(); 
         message.Add("Command", "Price"); 
         message.Add("ID", idx); 
			
         response = await this.inventoryService.SendMessageAsync(message);
			
         if (response.Status == AppServiceResponseStatus.Success){
            // Get the data that the service sent to us. 
            if (response.Message["Status"] as string == "OK") {
               result += " : Price = " + "$"+ response.Message["Result"] as string; 
            } 
         }
			
         textBlock.Text = result;  
      } 
   } 
}

要运行此应用程序，您需要在解决方案资源管理器中将ClientApp 项目设置为启动项目，然后从生成>部署解决方案部署此解决方案。

APP Services

编译并执行上述代码后，您将看到以下窗口。在应用服务中，我们只添加了两个项目的资料。因此，您可以输入 0 或 1 来获取这些项目的资料。

APP Services

当您输入 0 并单击按钮时，它将运行应用服务作为后台任务，并在文本块上显示项目信息。

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