cancel GetAsync request from outside of method

Question

I have large numbers of async requests. At some point, when application is deactivated (paused) I need cancel all requests. I'm looking for a solution to cancel requests outside of async method. can someone point me in a right direction?

Here is chunks of code.

The async method:

public async void GetDetailsAsync(string url)
{
    if (this.LastDate == null)
    {
        this.IsDetailsLoaded = "visible";
        NotifyPropertyChanged("IsDetailsLoaded");
        Uri uri = new Uri(url);
        HttpClient client = new HttpClient();
        HtmlDocument htmlDocument = new HtmlDocument();
        HtmlNode htmlNode = new HtmlNode(0, htmlDocument, 1);
        MovieData Item = new MovieData();
        string HtmlResult;

        try
        {
            HtmlRequest = await client.GetAsync(uri);
            HtmlResult = await HtmlRequest.Content.ReadAsStringAsync();
        }
        ...

calling method:

for (int i = 0; i < App.ViewModel.Today.Items.Count; i++)
{
    App.ViewModel.Today.Items[i].GetDetailsAsync(App.ViewModel.Today.Items[i].DetailsUrl);
}

deactivate event:

private void Application_Deactivated(object sender, DeactivatedEventArgs e)
{
    //Here i need to stop all requests.
}

My best guess is some method which cancels all requests at once. — Rovshan Mamedov, Feb 14 '14 at 18:15
What did you try? Did you declare `CancellationToken` out of methods(as your class's private field?) as it is shared by two methods. — L.B, Feb 14 '14 at 18:15
I declared cancelationTokenSource as public field. (I can't access privet from outside) asd included token at GetAsync method — Rovshan Mamedov, Feb 14 '14 at 18:21
possible duplicate of [Cancelling file download with httpclient and asynctask](http://stackoverflow.com/questions/5080500/cancelling-file-download-with-httpclient-and-asynctask) — usr, Feb 14 '14 at 18:21
*All* TPL cancellation questions are duplicate by now. Please search. — usr, Feb 14 '14 at 18:21
Believe me, I looked at this. I need a mass destruction of all treads at app at same time. :) — Rovshan Mamedov, Feb 14 '14 at 18:23
You need to shut down all tasks individually. Search "cancel httpclient". — usr, Feb 14 '14 at 18:28
httpclient.CancelPendingRequests. I tried this one too. This method cancels requests at current instance. I don't see any way how I can call this from outside of method. — Rovshan Mamedov, Feb 14 '14 at 18:32
to usr: this post you mentioned at top of my question is about asynktask for Java-Android. — Rovshan Mamedov, Feb 14 '14 at 18:37

score 14 · Accepted Answer · answered Feb 14 '14 at 18:44

You just create a single (shared) instance of CancellationTokenSource:

private CancellationTokenSource _cts = new CancellationTokenSource();

Then, tie all asynchronous operations into that token:

public async void GetDetailsAsync(string url)
{
  ...
  HtmlRequest = await client.GetAsync(uri, _cts.Token);
  ...
}

Finally, cancel the CTS at the appropriate time:

private void Application_Deactivated(object sender, DeactivatedEventArgs e)
{
  _cts.Cancel();
  _cts = new CancellationTokenSource();
}

That worked :) Deactivated method was in different file than async methods so I made a static method CancelAllThreads(); and called it from App.xaml.cs. — Rovshan Mamedov, Feb 14 '14 at 20:26

cancel GetAsync request from outside of method

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