我有一个后台任务，它是由时间触发器触发的。这个任务在手机重启后会自动重新启动，而无需首先加载应用程序。也许这会有所帮助...
[编辑]刚才意识到我的回答有点晚了...
这类似于这个问题：如何在应用程序启动时停止后台任务？
最简单的方法是将您的任务转换为进程内后台任务：https://learn.microsoft.com/zh-cn/windows/uwp/launch-resume/convert-out-of-process-background-task
使用进程内任务，您可以直接从后台活动中检查应用程序是否在前景中。
如果您需要将后台任务保持为与主要应用程序分离的进程，则可以执行以下操作之一：
var value = ApplicationSettingsHelper.ReadResetSettingsValue(ApplicationSettingsConstants.AppState);
if (value == null)
foregroundAppState = AppState.Unknown;
else
foregroundAppState = EnumHelper.Parse<AppState>(value.ToString());
if (foregroundAppState == AppState.Suspended)
//Do something
else if (foregroundAppState == AppState.Active)
return;
else if (foregroundAppState == AppState.Unknown)
return;
实现这个的方法是使用应用程序本地设置。
在前台和后台设置该设置。 例如，在前台执行以下操作。
/// <summary>
/// When the window visibility changes
/// </summary>
/// <param name="sender">object sender</param>
/// <param name="e">VisibilityChangedEventArgs e</param>
private void OnVisibilityChanged(object sender, VisibilityChangedEventArgs e)
{
var localSettings = ApplicationData.Current.LocalSettings;
if (!e.Visible)
{
localSettings.Values["AppInForeground"] = false;
}
else
{
localSettings.Values["AppInForeground"] = true;
}
}
我非常希望看到一个更简单的解决方案。如果没有，您可以实施一个仲裁机制。大致如下：
public class AppSynchronization
{
// Called by the main app on launch or on resume. It will signal the main app's intention to start.
// The main app will not perform any significant actions before this method returns.
public void ActivateMainApp() {...}
// Called by the main app. It will signal the fact that the main app is "going away".
public async Task MainAppSuspended() {...}
// Called by the background agent.
// It will signal the background agent intention to start.
// This method will only return if the main app is out of the way.
// It will return a cancellation token that will be used to cancel the activity of the background agent when the main app advertises its intention to start.
public async Task<CancellationToken> ActivateBackgroundAgent(CancellationToken cancelWait)
{
// Make sure the main app is not started or wait until the main app is out of the way
// Start a thread that is on the lookout for the main app announcing that it wants to start.
// When that happens it will cancel the cancellation token returned.
}
// <summary>
// Called by the background agent.
// It will signal the fact that the background agent completed its actions.
public async Task DeactivateBackgroundAgent()
}
private AppSynchronization appSynchronization;
public App()
{
...
this.appSynchronization = new AppSynchronization();
}
protected async override void OnLaunched(LaunchActivatedEventArgs e)
{
...
if (rootFrame.Content == null)
{
// Advertise the fact that the main app wants to start.
// The background agent will know to cancel whatever its doing.
// ActivateMainApp may have to be async although you need to make sure that OnLaunched supports that
this.appSynchronization.ActivateMainApp();
...
}
}
private async void OnResuming(object sender, object e)
{
...
// Advertise the fact that the main app wants to resume.
// The background agent will know to cancel whatever its doing.
this.appSynchronization.ActivateMainApp();
}
private async void OnSuspending(object sender, SuspendingEventArgs e)
{
var deferral = e.SuspendingOperation.GetDeferral();
...
// Advertise the fact that the main app is suspending.
// The background agent will know it is allowed to start doing work.
await _mainAppSynchronization.MainAppSuspended();
...
deferral.Complete();
}
private void OnUnhandledException(object sender, UnhandledExceptionEventArgs e)
{
...
// Advertise the fact that the main app is going away.
// The background agent will know it is allowed to start doing work.
_mainAppSynchronization.MainAppSuspended().Wait();
}
而在后台代理中：
public sealed class BackgroundTask : IBackgroundTask
{
public async void Run(IBackgroundTaskInstance taskInstance)
{
...
AppSynchronization appSynchronization = new AppSynchronization();
BackgroundTaskDeferral deferral = taskInstance.GetDeferral();
// Make sure that the main app is not started. If it is started then wait until the main app gets out of the way.
// It he main app is running this will wait indefinitely.
// Use backgroundAgentCancellationToken to cancel the actions of the background agent when the main app advertises its intention to start.
CancellationToken backgroundAgentCancellationToken = await appSynchronization.ActivateBackgroundAgent();
await DoBackgroundAgentWork(backgroundAgentCancellationToken)
// Advertise the fact that the background agent is out.
// DeactivateBackgroundAgent will make sure that the synchronization mechanism advertised the fact that the background agent is out.
// DeactivateBackgroundAgent may have to be declared async in case the synchronization mechanism uses async code to do what is needed.
await appSynchronization.DeactivateBackgroundAgent();
deferral.Complete();
}
我不确定在UWP中是否有任何跨进程通信的方法。仲裁机制本身可能必须基于本地存储上的文件。
仲裁机制可能还必须包括一个心跳机制，以防其中一个进程以灾难性的方式崩溃。