How to use the CancellationToken property?
You can create a Task with cancellation token, when you app goto background you can cancel this token.
You can do this in PCL https://developer.xamarin.com/guides/xamarin-forms/application-fundamentals/app-lifecycle
var cancelToken = new CancellationTokenSource();
Task.Factory.StartNew(async () => {
await Task.Delay(10000);
// call web API
}, cancelToken.Token);
//this stops the Task:
cancelToken.Cancel(false);
Anther solution is user Timer in Xamarin.Forms, stop timer when app goto background https://xamarinhelp.com/xamarin-forms-timer/
You can implement your work method as follows:
private static void Work(CancellationToken cancelToken)
{
while (true)
{
if(cancelToken.IsCancellationRequested)
{
return;
}
Console.Write("345");
}
}
That's it. You always need to handle cancellation by yourself - exit from method when it is appropriate time to exit (so that your work and data is in consistent state)
UPDATE: I prefer not writing while (!cancelToken.IsCancellationRequested)
because often there are few exit points where you can stop executing safely across loop body, and loop usually have some logical condition to exit (iterate over all items in collection etc.). So I believe it's better not to mix that conditions as they have different intention.
Cautionary note about avoiding CancellationToken.ThrowIfCancellationRequested()
:
Comment in question by Eamon Nerbonne:
... replacing
ThrowIfCancellationRequested
with a bunch of checks forIsCancellationRequested
exits gracefully, as this answer says. But that's not just an implementation detail; that affects observable behavior: the task will no longer end in the cancelled state, but inRanToCompletion
. And that can affect not just explicit state checks, but also, more subtly, task chaining with e.g.ContinueWith
, depending on theTaskContinuationOptions
used. I'd say that avoidingThrowIfCancellationRequested
is dangerous advice.