Windows Phone-Web客户端请求未执行

Question

/* While writing this question , and testing stuff , i managed to answer the question, I'm sharing my findings so they would be of help to some other poor soul. Please see answer below. */

I'm trying to fetch a JSON data from my API in a background task. I have the background task nice and running doing it's thing , but when i try to get the data , nothing happens ?!?

here is the code i use :

    protected override void OnInvoke(ScheduledTask task)
    {

        string wurl = @"http://test.com/api/stuff/getdata";

        WebClient webClient = new WebClient();
        webClient.DownloadStringCompleted += new DownloadStringCompletedEventHandler(webClient_DownloadStringCompleted);
        webClient.DownloadStringAsync(new Uri(wurl));


        NotifyComplete();

    }

and that's all ... the webClient_DownloadStringCompleted never gets executed.

Answer 1

The key thing here is that the WebClient executes its method asynchronously and NotifyComplete() gets executed before the WebClient has the chance to fetch the data.

When you call NotifyComplete() , it notifies the OS that you are done executing your task and the system should terminate it.

The solution is to move NotifyComplete() at the end of the async method webClient_DownloadStringCompleted ( in this case) and ... voala !

Warning 1: You have up to 25 seconds to finish whatever you are doing , otherwise the task gets terminated.

Warning 2: Your background task cannot consume more than (on some phones ) 6 MB (on the emulator i tested with windows phone 8) 10 MB of memory! if your background task does , it will be terminated.

It's good to consider using Resource Intensive background task if your app is going to consume more memory and time ( up to 10 minutes) , note this type of task is only available while the phone is charging!