How to correctly manage ASynkTaks in Tabs which have the same fragment class

I have a FragmentActivity with 7 tabs, and all of them refers to the same fragment, the only difference is a parameter, that makes them to load throught an ASyncTask the data to show from a PHP that returns a JSON. My problem is that when I swipe from one tab to another, if the task from the first tab is still loading, it loads in the new tab, or crash, or doesnt do anything. However, the activity load two tabs, so the task is launched twice and is the same problem. Any idea?

Answers


While AsyncTasks are wonderful to have, they are intended to be procedures that are independent of any UI (e.g. saving information). For the longest time I was in the same boat and used AsyncTasks for work that would end up changing the UI (since hey, they have an onPost method).

What you should be using for any work that will affect the UI is called a Loader which will pay attention to the UI state of the Fragment. In your case the AsyncTask is probably attempting to access a UI element that no longer exists (View Pagers only keep the previous, current, and next views in memory). The Loader will pay attention to this and not attempt to change the UI.

There are plenty of examples out on the web, but in short you will need to create (extend) a Loader for each of your AsyncTasks (I recommend AsyncTaskLoader, if you do pay attention to forceLoad) and add the callbacks (LoaderManager.LoaderCallbacks) to your Fragment. Then when you are ready to load call getLoaderManager().restartLoader(LOADER_ID, bundle_args, loader_callback);


Keep a reference of your AsyncTask. I assume you have a callback which let's you know when the tabs have changed. When you get notified that tabs have changed you can check if your AsyncTask is null or not finished yet, if it isn't you call it's cancel() method.

if(asyncTask!=null && asyncTask.getStatus()!=AsyncTask.Status.FINISHED) {
    asyncTask.cancel(false);
    asyncTask = null;
}

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