How do I get sharedpreferences in Asynctask?

Question

I am writing an android application for my school project but i am stuck here. The problem is i have to access a SharedPreferences value and need it in an AsyncTask class. When I try to access it, it wont let me because of the context. How can i reach my SharedPreferences in my AsyncTask?

public class CheckAccess extends AsyncTask<JSONObject, Integer, Boolean>{


    @Override
    protected Boolean doInBackground(JSONObject... params) {

        //Trying to get sharedpreferences here wont work.

        return null;
    }

}

Solution 1

Override onPreExecute or onPostExecute method of AsyncTask and get SharedPreferences there:

@Override
protected void onPreExecute() {
    super.onPreExecute();
    //get sharedPreferences here
    SharedPreferences sharedPreferences = getSharedPreferences(<SharedPreferencesName>, <Mode>);
}

Please note that getSharedPreferences is an Activity method. So, you need to call it through Context if you are not using it in Activity.

Solution 2

You can get SharedPreferences in a background thread using the PreferenceManager like this:

SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(<YourActivity>.this);

Solution 3

You can get SharedPreferences in the background using an AsyncTask.

The mistake is in this line, where you are passing in the wrong type of variable:

SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(this);

In your case, the word this refers to the AsyncTask instance that you are calling if from.

---

What I do is I pass the Context in to the task in the execute() method. See the code below for a working example:

    new AsyncTask<Context, Void, String>()
    {
        @Override
        protected String doInBackground(Context... params)
        {
            Context context = params[0];
            SharedPreferences prefs =
                    context.getSharedPreferences("name of shared preferences file",
                            Context.MODE_PRIVATE);

            String myBackgroundPreference = prefs.getString("preference name", "default value");

            return myBackgroundPreference;
        }

        protected void onPostExecute(String result)
        {
            Log.d("mobiRic", "Preference received in background: " + result);
        };

    }.execute(this);

In the above example, this refers to the Activity or Service that I call this from.

Comments

[user3316779]

Good idea, but i am having trouble with getting it. How to continue this line in preExecute? SharedPreferences prefs = ...

[user3316779]

I think the problem is that i don't call it through Context since i am not using it in an activity. How can i do it?

[Alejandro Alcalde]

Simply pass the context to the AsynTask constructor.

[Alejandro Alcalde]

Then you can not get the preferences I think. You need the Activity

[Green goblin]

You must be using the AsynTask class from an activity. Before calling it, call the constructor of class where Asynctask is residing. In the constructor, pass the context.

[user3316779]

I am using it like this: jsonObject = new GetData().execute(cardId).get(); What changes do i need?

[Green goblin]

Define a constructor of CheckAccess to accept Context. In the constructor definition, initialize Context. Pass the Context while creating object.

[Richard Le Mesurier]

I'm afraid this answer is wrong. See tlahoda's answer for a summary or my answer for a more detailed explanation.

[Green goblin]

@RichardLeMesurier: Thanks for correcting me. I totally missed it. I have corrected my answer