c# - Xamarin 表单后台任务仅在 ios 上打开应用程序时运行
<p><ol>
<li>预期行为
<ul>
<li>ios
<ul>
<li>当应用最小化且每 5 秒收到通知时。</li>
</ul></li>
<li>安卓
<ul>
<li>当应用最小化且每 5 秒收到通知时。</li>
</ul></li>
</ul></li>
<li>实际行为
<ul>
<li>ios
<ul>
<li>应用最小化并且没有通知进来，打开应用会导致通知每 5 秒进来一次。</li>
</ul></li>
<li>安卓
<ul>
<li>当应用最小化并且每 5 秒收到一次通知时。
<blockquote>
<pre><code>//from app.xaml.cs
protected override void OnSleep()
{
void ScheduleNotification()
{
// Start a timer that runs after 5 seconds.
Device.StartTimer(TimeSpan.FromSeconds(5), () =>
{
System.Threading.Tasks.Task.Factory.StartNew( () =>
{
// Do the actual request and wait for it to finish.
PerformNotification();
// Switch back to the UI thread to update the UI
Device.BeginInvokeOnMainThread(() =>
{
// Update the UI
// ...
// Now repeat by scheduling a new request
ScheduleNotification();
count++;
});
}, CancellationToken.None, TaskCreationOptions.DenyChildAttach, TaskScheduler.Default);
// Don't repeat the timer (we will start a new timer when the request is finished)
return false;
});
}
void PerformNotification()
{
CrossLocalNotifications.Current.Show("title", "body"+ count.ToString());
}
ScheduleNotification();
}
</code></pre>
</blockquote> </li>
</ul></li>
</ul></li>
</ol></p>
<br><hr><h1><strong>Best Answer-推荐答案</ strong></h1><br>
<p><p>在 iOS 上，不要求在后台运行的应用程序在后台运行的时间不能超过 10 秒。为了让一些代码在后台运行，您可以在 iOS 和 android 上实现 DependencyService。您可以将以下代码放入 iOS 上的该服务中:</p>
<pre><code>public async Task RunCodeInBackgroundMode(Func<Task> action, string name = "MyBackgroundTaskName")
{
nint taskId = 0;
var taskEnded = false;
taskId = UIApplication.SharedApplication.BeginBackgroundTask(name, () =>
{
//when time is up and task has not finished, call this method to finish the task to prevent the app from being terminated
Console.WriteLine($"Background task '{name}' got killed");
taskEnded = true;
UIApplication.SharedApplication.EndBackgroundTask(taskId);
});
await Task.Factory.StartNew(async () =>
{
//here we run the actual task
Console.WriteLine($"Background task '{name}' started");
await action();
taskEnded = true;
UIApplication.SharedApplication.EndBackgroundTask(taskId);
Console.WriteLine($"Background task '{name}' finished");
});
await Task.Factory.StartNew(async () =>
{
//Just a method that logs how much time we have remaining. Usually a background task has around 180 seconds to complete.
while (!taskEnded)
{
Console.WriteLine($"Background task '{name}' time remaining: {UIApplication.SharedApplication.BackgroundTimeRemaining}");
await Task.Delay(1000);
}
});
}
</code></pre>
<p>在 Android 上，您可以使用以下代码:</p>
<pre><code>public async Task RunCodeInBackgroundMode(Func<Task> action, string name = "MyBackgroundTaskName")
{
var powerManager = (PowerManager)Application.Context.GetSystemService(Context.PowerService);
var wakeLock = powerManager.NewWakeLock(WakeLockFlags.Partial,
name);
//acquire a partial wakelock. This prevents the phone from going to sleep as long as it is not released.
wakeLock.Acquire();
var taskEnded = false;
await Task.Factory.StartNew(async () =>
{
//here we run the actual code
Console.WriteLine($"Background task '{name}' started");
await action();
Console.WriteLine($"Background task '{name}' finished");
wakeLock.Release();
taskEnded = true;
});
await Task.Factory.StartNew(async () =>
{
//just a method to keep track of how long the task runs
var stopwatch = new Stopwatch();
stopwatch.Start();
while (!taskEnded)
{
Console.WriteLine($"Background '{name}' task with wakelock still running ({stopwatch.Elapsed.TotalSeconds} seconds)");
await Task.Delay(1000);
}
stopwatch.Stop();
});
}
</code></pre>
<p>在共享项目中，您可以通过以下方式调用这些方法:</p>
<pre><code>var deviceInfoServic = ServiceLocator.Instance.Get<YourService Interface here>();
await deviceInfoServic.RunCodeInBackgroundMode(async () =>
{
//your code here
});
</code></pre></p>
<p style="font-size: 20px;">关于c# - Xamarin 表单后台任务仅在 ios 上打开应用程序时运行，我们在Stack Overflow上找到一个类似的问题：
<a href="https://stackoverflow.com/questions/49542832/" rel="noreferrer noopener nofollow" style="color: red;">
https://stackoverflow.com/questions/49542832/
</a>
</p>
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