HttpPost inside getView from Adapter

Question

I have a Listview with multiple items, in every item there is 2 buttons. What i want to do is when i click on a button, it sends some data to server through the HttpPost. I put a Thread inside my Adapter.getView() but it's not working because the Adapter is aleady in an Async Thread. Have you an idea about how can i make it work?

My ListView :

// ... OnCreate ListView ...
// ... new ListAppTask().execute();
// ...
public class ListAppTask extends AsyncTask<Void, Void, List<ProductExtended>> {

    protected List<ProductExtended> doInBackground(Void... args) {
        Product product = new Product();
        List<ProductExtended> products = product.getLastProducts(getApplicationContext());

        return products;
    }

    protected void onPostExecute(List<ProductExtended> result) {
        data.addAll(result);
        adapter.notifyDataSetChanged();
        if (progressDialog != null) {
            progressDialog.dismiss();
            progressDialog = null;
        }
    }
}

My Adapter :

    public class PackageAdapter extends BaseAdapter {

        private List<ProductExtended> data;
        private Context context;

        public PackageAdapter(Context context, List<ProductExtended> data) {
            this.context = context;
            this.data = data;
        }

        @Override
        public int getCount() {
            return data.size();
        }

        @Override
        public ProductExtended getItem(int position) {
            return data.get(position);
        }

        @Override
        public long getItemId(int position) {
            return position;
        }

        @Override
        public View getView(final int position, View convertView, ViewGroup parent) {
            final ProductExtended item = getItem(position);
            ViewHolder holder;
            if (convertView == null) {
                LayoutInflater li = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
                convertView = li.inflate(R.layout.package_row, parent, false);
                holder = new ViewHolder();
                holder.btnBa = (LinearLayout) convertView.findViewById(R.id.idBonneaffaire);
                holder.btnJl = (LinearLayout) convertView.findViewById(R.id.idJelai);
                convertView.setTag(holder);
            } else {
                holder = (ViewHolder) convertView.getTag();
            }


            holder.btnBa.setOnClickListener(new OnClickListener() {

                @Override
                public void onClick(View v) {

                        new Thread() {

                            @Override
                            public void run() {
                                // ---------------- PROBLEM HERE -------------------
                                HttpClient httpclient = new DefaultHttpClient();
                                HttpPost httppost = new HttpPost("My URL");
                                // Execute HTTP Post Request
                                try {
                                    HttpResponse response = httpclient.execute(httppost);
                                    String reponse = EntityUtils.toString(response.getEntity());

                                } catch (UnknownHostException e) {
                                } catch (HttpHostConnectException e) {
                                } catch (ClientProtocolException e) {
                                } catch (IOException e) {
                                }
                            }
                        }.start();
                }
            });

          // Same for the second LinearLayout considered as Button



            return convertView;
        }

        static class ViewHolder {
            LinearLayout btnBa;
            LinearLayout btnJl;
        }

And the error diplayed :

Only the original thread that created a view hierarchy can touch its views. adapter

Thank's, Akram

As usual, the folks would enjoy a code snippet, and your precise error code ('not working=?'). Also- out of interest could you be more precise about what you mean that your adapter is in an Async Thread- strictly speaking it should only update on the UI thread. Thanks. — Tom, Jul 01 '13 at 21:58

score 2 · Accepted Answer · answered Jul 01 '13 at 22:38

This error mainly describe that your are trying to update the UI from another thread than the main one. This happen if for whatever reason you try to touch your view in the Run methods of your threads trown by your onClickListener. It is not visible in your example but can you check what your doing where you stated "// Same for the second LinearLayout considered as Button" ?

To prevent this exception from happening you can use android.os.Handler to execute Runnable on the main thread whenever you need to update the UI.

For instance:

Handler mHandler = new Handler();

@Override
public View getView(final int position, View convertView, ViewGroup parent) {
    final ViewHolder holder;
    if(convertView == null){
        convertView = mInflater.inflate(R.layout.item_simple_row, parent, false);
        holder = new ViewHolder();
        holder.textView = (TextView) convertView.findViewById(R.id.txt);
        holder.button = (Button) convertView.findViewById(R.id.btn);
        convertView.setTag(holder);
    }else{
        holder = (ViewHolder) convertView.getTag();
    }

    final String url = getItemAtPosition(position);
    holder.textView.setText(url);
    holder.button.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View v) {
            final Thread worker = new Thread(new Runnable(){

                @Override
                public void run()
                {
//WATCH OUT IF YOU TOUCH YOUR VIEW HERE WITHOUT USING A HANDLER YOU MAY GET THE ERROR YOUR ARE TALKING ABOUT

                    HttpGet request = new HttpGet(url);
                    DefaultHttpClient httpClient = new DefaultHttpClient();
                    try {
                        final HttpResponse response = httpClient.execute(request);

                        mHandler.post(new Runnable() {

                            @Override
                            public void run() {
//UPDATE YOUR UI HERE
                                holder.textView.setText(url+ " : " +response.getStatusLine());
                            }
                        });

                    } catch (ClientProtocolException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    } catch (IOException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
                }
            });

            worker.start();


        }
    });

    return convertView;
}

The problem is that i didn't set the Thread "final", Thank you for your answer. — Akram Fares, Jul 01 '13 at 23:10

score 1 · Answer 2 · edited Jun 20 '20 at 09:12

I prefer keeping things simple. Thread and Handler are important java and android concepts respectively, but doing http in response to UI events is so common in Android they've invented an amazing helper called AsyncTask.

Create an anonymous instance of this class with an inner reference to the enclosing Activity class (i.e. in practical terms, define the class inside your activity and don't make it static). It's these kind of features of Java that the developers had in mind when designing Android UI and threading patterns.

From the docs above:

When an asynchronous task is executed, the task goes through...

doInBackground(Params...), invoked on the background thread immediately after onPreExecute() finishes executing. This step is used to perform background computation that can take a long time. ...

onPostExecute(Result), invoked on the UI thread after the background computation finishes. The result of the background computation is passed to this step as a parameter.

[I've ommited extra details, also my emphasis].

Your adapter's getView should refer to an async task, which passes information from a code block executed with all your syncronous http requests in it off the UI thread, to a code block on the UI thread that can be used to touch its views (you update your listview here).

NB Dont' forget to check your listview is still relevant for that data after the task has finished, or, because of AbsListView view recycling, you'll risk putting data into apparently the wrong cell.

Best,

Tom.

HttpPost inside getView from Adapter

2 Answers2