WinRT的BackgroundTask

BackgroundTask与主进程是不同的进程，所以BackgroundTask不能更新主UI，但是可以更新tile，发toast消息和读写文件。

至少要执行一次主进程以激活BackgroundTask。

实现步骤：

1，实现后台任务的逻辑代码，必须是一个WinRt Component，例如：

namespace MyApp.BackgroundTasks { // NOTE: determines filename "MyApp.BackgroundTasks.WinMD"using Windows.ApplicationModel.Background; // For IBackgroundTask & IBackgroundTaskInstance// NOTE: WinRT components MUST be public and sealedpublic sealed class MyBackgroundTask : IBackgroundTask {public void Run(IBackgroundTaskInstance taskInstance) {// Register cancelation handler (see the "Background task cancellation" section)// NOTE: Once canceled, a task has 5 seconds to complete or the process is killedtaskInstance.Canceled +=(IBackgroundTaskInstance sender, BackgroundTaskCancellationReason reason) => {// TODO: Tell task it should cancel itself as soon as possible...};// Recommended: Adjust task behavior based on CPU and network availability// For example: A mail app could download mail for all folders when cost is// low and only download mail for the Inbox folder when cost is highswitch (BackgroundWorkCost.CurrentBackgroundWorkCost) {case BackgroundWorkCostValue.Low: // The task can use CPU & networkcase BackgroundWorkCostValue.Medium: // The task can use some CPU & networkcase BackgroundWorkCostValue.High: // The task should avoid using CPU & network// This example records the last trigger time in an application data setting// so the app can read it later if it chooses. We do regardless of work cost.ApplicationData.Current.LocalSettings.Values["LastTriggerTime"] =DateTimeOffset.Now;break;}}}}

把逻辑写在IBackgroundTask接口的Run函数中。

2，决定使用哪个触发器

后台任务只有在某个条件触发后才会执行。这些触发器包括：

Trigger触发条件频率是否需要锁屏宿主进程MaintenanceTrigger交流电每15分钟一次1次或多次 BackgroundTaskHost.exeTimeTrigger同上，电池也可以1次或多次是BackgroundTaskHost.exeSystemTrigger 1次或多次 BackgroundTaskHost.exeLocationTrigger进入或离开Geofence多次 BackgroundTaskHost.exePushNotificationTrigger收到推送多次是BackgroundTaskHost.exe或App自身ControlChannelTrigger实时通信多次 App

MaintenanceTrigger和TimeTrigger每天最多执行96次（每15分钟）。可以配置让他们只执行一次。

MaintenanceTrigger用于执行不急的任务，比如更新推送，更新tile，发toast，原始推送等。

TimeTrigger用于执行紧急的任务，比如检查邮件。

SystemTrigger在某些系统事件触发时执行，比如：

• 当连上网时，
• 网络状态切换时（3G/WiFi），
• 安装新版本的App时，
• 登陆的微软账户变化时，
• 时区改变时，
• 收到短信时，
• App被添加到锁屏桌面时
• App从锁屏桌面移除时
• 后台任务的性能成本变化时
• 用户从离开变成回来（输入）时
• 用户从活跃到离开时（4分钟无输入）
• 用户登陆时
• 网络连接被重置需要重新连接时

LocationTrigger用于当用户进入某个区域时提示团购之类的信息。比如：

private async Task InitializeGeofenceMonitorAsync() {// Get a reference to the app's singleton GeofenceMonitor objectGeofenceMonitor gm = GeofenceMonitor.Current;gm.Geofences.Clear(); // Erase all its Geofence objects// Get the PC's current location (requires Location capability)Geoposition geoposition = await new Geolocator().GetGeopositionAsync();// Register a Geofence whose state changes whenever the PC goes within 1 meter of itGeofence gf = new Geofence("InitialPCLocation", // Geofence Idnew Geocircle(geoposition.Coordinate.Point.Position, 1), // Point & radiusMonitoredGeofenceStates.Entered | MonitoredGeofenceStates.Exited, // When task should runfalse, // Not 1 timeTimeSpan.FromSeconds(5), // Dwell timeDateTimeOffset.UtcNow, // Start timeTimeSpan.FromHours(1)); // Durationgm.Geofences.Add(gf); // Add the Geofence object to the GeofenceMonitor's collection}

public sealed class GeofenceLocationTask : IBackgroundTask {public void Run(IBackgroundTaskInstance taskInstance) {IReadOnlyList<GeofenceStateChangeReport> reports = GeofenceMonitor.Current.ReadReports();foreach (GeofenceStateChangeReport report in reports) {// This loop processes a report for each Geofence object that changed// Each report includes the Geofence object affected, its position,// the NewState of the Geofence (Entered or Exited), and the reason why// the report was generated (Used or Expired):Geofence geofence = report.Geofence; // The Geofence object affectedGeoposition pos = report.Geoposition; // The Geofence object’s positionGeofenceState state = report.NewState; // Entered or ExitedGeofenceRemovalReason reason = report.RemovalReason; // Used or Expired// TODO: Process the Geofence object affected here...}}}

PushNotificationTrigger用于实时通信的应用，比如邮件，IM，VOIP。应用必须被添加到锁屏。

ControlChannelTrigger也用实时通信的应用，当低电量时也可以工作。当连接着socket的时候，用于legacy的通信协议。

3，添加manifest声明

Executable字段，一般留空。

Entry Point字段指定类名（包括namespace）

注意：锁屏App可以在低电量时运行

4，注册BackgroundTask

var btb = new BackgroundTaskBuilder {Name = "Some friendly name", // See the "Debugging background tasks" section// Specify the full name of the class implementing the IBackgroundTask interface// You could specify a literal string here, but I prefer to do it this// way to get compile-time safety and rename refactoring supportTaskEntryPoint = typeof(Wintellect.BackgroundTasks.SystemTriggerTask).FullName};// Specify the desired trigger (TimeTrigger, MaintenanceTrigger, SystemTrigger,// LocationTrigger, or PushNotificationTrigger). This example uses a TimeTriggerbtb.SetTrigger(new TimeTrigger(freshnessTime: 60, oneShot: false));// Optional: add 1+ system conditions and// indicate whether the task should stop if any condition is lostbtb.AddCondition(new SystemCondition(SystemConditionType.InternetAvailable));btb.CancelOnConditionLoss = true; // System tells task to cancel if any condition is lost// Register the task with WindowsBackgroundTaskRegistration registeredTask = btb.Register();// Use registeredTask to Unregister, or if the app wants Progress/Completed notifications

资源限额：

注意后台任务不是24小时执行的。