How to pass the application context to the Adapter by reading Json using Asynctask?

Question

private class GetEmpresas extends AsyncTask<Void, Void, Void> {

... 

@Override
    protected Void doInBackground(Void... arg0) {
        // Creating service handler class instance
        ServiceHandler sh = new ServiceHandler();

        // Making a request to url and getting response
        String jsonStr = sh.makeServiceCall(url, ServiceHandler.GET);

        //Log.d("Response: ", "> " + jsonStr);

        if (jsonStr != null) {

            try {
                JSONObject jsonObj = new JSONObject(jsonStr);

                // Getting JSON Array node
                empresasJson = jsonObj.getJSONArray(TAG_EMPRESAS);

                // looping through All Contacts
                for (int i = 0; i < empresasJson.length(); i++) {

                    JSONObject c = empresasJson.getJSONObject(i);

                    String id = c.getString(TAG_ID);
                    String name = c.getString(TAG_NOME);
                    String cidade = c.getString(TAG_CIDADE);
                    String endereco = c.getString(TAG_ENDERECO);

                    // tmp hashmap for single contact
                    HashMap<String, String> contact = new HashMap<String, String>();

                    // adding each child node to HashMap key => value
                    contact.put(TAG_ID, id);
                    contact.put(TAG_NOME, name);
                    contact.put(TAG_CIDADE, cidade);
                    contact.put(TAG_ENDERECO, endereco);

                                                    empresas = new ArrayList<Empresas>();

                    Empresas item = new Empresas(name,endereco, R.drawable.logo);

                    empresas.add(item);

                    adapter = new AdapterEmpresas(empresas, ?????);

                    listView.setAdapter(adapter);

                }
            } catch (JSONException e) {
                e.printStackTrace();
            }
        } else {
            Log.e("ServiceHandler", "Couldn't get any data from the url");
        }

        return null;
    }

     ....

}

ERROR

01-30 18:21:25.058: E/AndroidRuntime(8276): FATAL EXCEPTION: AsyncTask #1
01-30 18:21:25.058: E/AndroidRuntime(8276): java.lang.RuntimeException: An error occured while executing doInBackground()
01-30 18:21:25.058: E/AndroidRuntime(8276):     at android.os.AsyncTask$3.done(AsyncTask.java:299)
01-30 18:21:25.058: E/AndroidRuntime(8276):     at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:352)
01-30 18:21:25.058: E/AndroidRuntime(8276):     at java.util.concurrent.FutureTask.setException(FutureTask.java:219)
01-30 18:21:25.058: E/AndroidRuntime(8276):     at java.util.concurrent.FutureTask.run(FutureTask.java:239)
01-30 18:21:25.058: E/AndroidRuntime(8276):     at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)
01-30 18:21:25.058: E/AndroidRuntime(8276):     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080)
01-30 18:21:25.058: E/AndroidRuntime(8276):     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573)
01-30 18:21:25.058: E/AndroidRuntime(8276):     at java.lang.Thread.run(Thread.java:856)
01-30 18:21:25.058: E/AndroidRuntime(8276): Caused by: java.lang.NullPointerException
01-30 18:21:25.058: E/AndroidRuntime(8276):     at com.solutudo.activities.Main$GetEmpresas.doInBackground(Main.java:137)
01-30 18:21:25.058: E/AndroidRuntime(8276):     at com.solutudo.activities.Main$GetEmpresas.doInBackground(Main.java:1)
01-30 18:21:25.058: E/AndroidRuntime(8276):     at android.os.AsyncTask$2.call(AsyncTask.java:287)
01-30 18:21:25.058: E/AndroidRuntime(8276):     at java.util.concurrent.FutureTask.run(FutureTask.java:234)
01-30 18:21:25.058: E/AndroidRuntime(8276):     ... 4 more

Question:

How do I pass the context of the method Adapter that gets the context?

Before loading the Json, I had created another class, and when I passed the this as a parameter, it worked correctly. Now in this other method it does not work.

Answer 1

I suggest some changes. First, the reason:

Operations related to the Android UI cannot be done in the InBackground method, as it does not run in the Main Thread. UI operations can only be performed on Main Thread. Thus, you should perform UI operations in the onPostExecute method, as it runs in Main Thread.

About the Context passage, the lucasb.Aquino suggestion is correct.

About the Nullpointerexception error, I believe it may be due to the inappropriate UI update point.

That way your code would look like this

The onCreate method

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    new GetEmpresas(this).execute();
}

Your Asynctask Getempresas

private class GetEmpresas extends AsyncTask<Void, Void, List<Empresas>> {

    private Context mContext;

    public GetEmpresas(Context context) {
        super();
        mContext = context;
    }

    @Override
    protected List<Empresas> doInBackground(Void... params) {

        ...

        return empresas;
    }

    @Override
    protected void onPostExecute(List<Empresas> listEmpresas) {
        super.onPostExecute(listEmpresas);

        adapter = new AdapterEmpresas(listEmpresas, mContext);

        listView.setAdapter(adapter);

    }

}

If Nullpointerexception persists, make more of your code available so that a better assessment of the problem is possible.

Answer 2

You can create a constructor that takes the context.

Declare within your Getbusiness class the mContext property as below:

private Context mContext;

And then create a constructor by passing Context.

public GetEmpresas(Context ctx){
    mContext = ctx;
}

Now in the call snippet you passed this, pass the mContext property.

adapter = new AdapterEmpresas(empresas, mContext);

Edit: in your Activity...

GetEmpresas getEmpresasAsync = new GetEmpresas(this);
getEmpresasAsync.execute();