pass ArrayList<HashMap<String, String>> in AsyncTask

Question

I did a bit of mistakes and I do not know how to get out. Originally, the code is this and it works:

public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        ArrayList<HashMap<String, String>> menuItems = new ArrayList<HashMap<String, String>>();

        XMLParser parser = new XMLParser();
        String xml = parser.getXmlFromUrl(URL); // getting XML
        Document doc = parser.getDomElement(xml); // getting DOM element

        NodeList nl = doc.getElementsByTagName(KEY_ITEM);
        // looping through all item nodes <item>
        for (int i = 0; i < nl.getLength(); i++) {
            // creating new HashMap
            HashMap<String, String> map = new HashMap<String, String>();
            Element e = (Element) nl.item(i);
            // adding each child node to HashMap key => value
            map.put(KEY_ID, parser.getValue(e, KEY_ID));
            map.put(KEY_NAME, parser.getValue(e, KEY_NAME));
            map.put(KEY_COST, parser.getValue(e, KEY_COST));

            // adding HashList to ArrayList
            menuItems.add(map);
        }

        // Adding menuItems to ListView
        ListAdapter adapter = new SimpleAdapter(this, menuItems,
                R.layout.list_item,
                new String[] { KEY_NAME, KEY_COST }, new int[] {
                        R.id.name, R.id.cost });

        setListAdapter(adapter);


    }

Now since I put in another activity, I should be in error. Studying a bit I saw that you need to utlizare the taskasync but do not know how to end. And this is the code:

public class TaskAsincrono  extends AsyncTask<ArrayList<String>, Void, ArrayList<String>> {
        @Override
        protected void onPreExecute(){
        }

        @Override
        protected void onProgressUpdate(Void[] values) {

        };

        @Override
        protected ArrayList<String> doInBackground(ArrayList<String>... params) {
            ArrayList<HashMap<String, String>> menuItems = new ArrayList<HashMap<String, String>>();

            XMLParser parser = new XMLParser();
            String xml = parser.getXmlFromUrl(URL); // getting XML
            Document doc = parser.getDomElement(xml); // getting DOM element

            NodeList nl = doc.getElementsByTagName(KEY_ITEM);
            // looping through all item nodes <item>
            for (int i = 0; i < nl.getLength(); i++) {
                // creating new HashMap
                HashMap<String, String> map = new HashMap<String, String>();
                Element e = (Element) nl.item(i);
                // adding each child node to HashMap key => value
                map.put(KEY_ID, parser.getValue(e, KEY_ID));
                map.put(KEY_NAME, parser.getValue(e, KEY_NAME));
                map.put(KEY_COST, parser.getValue(e, KEY_COST));

                // adding HashList to ArrayList
                menuItems.add(map);

            }

            return menuItems;
        }

        @Override
        protected void onPostExecute(ArrayList<String> success) {
            //se l'alert è visibile viene rimosso
            if(dialog.isShowing()) dialog.dismiss();

            ListAdapter adapter = new SimpleAdapter(this, menuItems,
                    R.layout.list_item,
                    new String[] { KEY_NAME, KEY_COST }, new int[] {
                            R.id.name, R.id.cost });

            setListAdapter(adapter);

        }

        @Override
        protected void onCancelled() {
            mAuthTask = null;
        }
    }

How can I do?

thank you very much

not work, I do not know how to pass arraylist to OnPostExecute. because the return menuItems; goes wrong — Valkyrie00
– Valkyrie00, Commented Jul 16, 2013 at 19:21
the result of doInbackground computation is a param to onPostExecute. Change your onpostExecute parm as ArrayList<HashMap<String, String>> success — Raghunandan
– Raghunandan, Commented Jul 16, 2013 at 19:25
Also change this AsyncTask<ArrayList<String>, Void, ArrayList<HashMap<String, String>>> — Raghunandan
– Raghunandan, Commented Jul 16, 2013 at 19:25
Since it is a parameter to your doInBackground method, you can also save it as a local member of AsyncTask and later refer to it in your onPostExecute method. — type-a1pha
– type-a1pha, Commented Jul 18, 2013 at 15:31

2 revs · Accepted Answer · 2013-08-22 07:26:22Z

Just follow the suggestions of Raghunandan.

If your return type is ArrayList < HashMap < String,String > then why you return ArrayList < Sting >.

Change it like:

public class TaskAsincrono  extends AsyncTask<ArrayList<String>, Void, ArrayList<String>>

to

public class TaskAsincrono  extends AsyncTask<String, Void, ArrayList<HashMap<String,String>>>

And Also :

 @Override
 protected ArrayList<String> doInBackground(ArrayList<String>... params)

to

    @Override
    protected ArrayList<HashMap<String,String>> doInBackground(String... params)

I think your in your program the doInBackground() needs the url as its argument, so you may change it from ArrayList < String > to simple String [] ..

your AsyncTask skeleton is something like:

    public class TaskAsincrono  extends AsyncTask<String, Void, ArrayList<HashMap<String, String>>> {

    @Override, 
    protected void onPreExecute(){
       //what you want to do before AsyncTask execution(runs on UI thread)
      ......................
    }

    @Override
    protected void onProgressUpdate(Void[] values) {
       //About updates.......... 
    };

    @Override
    protected ArrayList<HashMap<String, String>> doInBackground(String... params) {
        ArrayList<HashMap<String, String>> menuItems = new ArrayList<HashMap<String, String>>();

         for (String extraUrl : params) {
           //do all stuffs here 
           //like parse xml stuffs 
           //put them to hashmap then add the hashmap to arraylist(menuitems).... 
           }
           return menuItems;
       }
 }

Now you can fetch the ArrayList from outside of AsyncTask(like button onclick or from onCreate() ) like this.

 TaskAsincrono  task = new TaskAsincrono  ();
    try {
        ArrayList<HashMap<String, String>> arr = new ArrayList<HashMap<String, String>>();
        arr = task.execute(URL).get();

And also follow the Developer Link For AsyncTask to know more about it.

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