android.view.viewrootimpl $ fromwrongthreadexception android java

Question

I have Declare an interface:

public interface GetChildList{
        public void onGetChildList(List<String> list);
}

In my class (where I call fetchJSONChild() ) implement:

import com.example.hakslogin.GetChildList;

public class ChildActivity extends ActionBarActivity implements GetChildList {

    Button btn_home;
    Button btn_add;
    private HandleJSON obj;
    public String urlString = "http://192.168.x.xx:xxxx/getdb";

    List<String> child = new ArrayList<String>();
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_child);


        obj = new HandleJSON(urlString);
        child = obj.fetchJSONChild(this);
    }

    @Override
    public void onGetChildList(List<String> list) {
       //this method will be called after thread in fetchJSONChild ended
       child = list;
       //here you can work with your list

    }
}

Below is my fetchJSONChild :

public void fetchJSONChild(final GetChildList callBack){

        final List<String> child = new ArrayList<String>();
        Thread thread = new Thread(new Runnable(){

            @Override
            public void run() {

                try {

                    URL url = new URL("http://192.168.x.xx:xxxx/childform_list/0.0.0.0/8069/new_db/admin/123456");
                    HttpURLConnection conn = (HttpURLConnection) url.openConnection();
                    conn.setReadTimeout(30000 /* milliseconds */);
                    conn.setConnectTimeout(50000 /* milliseconds */);
                    conn.setRequestMethod("GET");
                    //conn.setRequestProperty("User-Agent", "GYUserAgentAndroid");
                    conn.setRequestProperty("Content-Type", "application/json");
                    conn.setDoInput(true);
                    //conn.setUseCaches (false);
                    // Starts the query
                    if (Build.VERSION.SDK != null && Build.VERSION.SDK_INT > 13) {

                        conn.setRequestProperty("Connection", "close"); 
                    }
                    conn.connect();

                    System.out.println("Before url.openStream()");
                    InputStream stream = conn.getInputStream();//.openStream();
                    System.out.println("After url.openStream()");
                    String data = convertStreamToString(stream);
                    // for examole data = "1,2,3";

                    child.addAll(Arrays.asList(data.split(","));
                    readAndParseJSON(data);
                    stream.close();

                    callBack.onGetChildList(child);
                } catch (Exception e) {

                    e.printStackTrace();
                }
            }
        });
        thread.start(); 
    }

All working fine and I am getting list on my ChildActivity in onGetChildList method.

But I want to populate list in the listview like below:

@Override
public void onGetChildList(List<String> list) {
   //this method will be called after thread in fetchJSONChild ended
    List<String> array = new ArrayList<String>();
   child = list;
   //onCreate(new Bundle()); 
   lv_child = (ListView)findViewById(R.id.lv_child); 
   String arr[]=child.toArray(new String[list.size()]);
   String[] Temp= new String[2];
          Temp[0] = arr[2].toString();
          array.add(Temp[0].split(":")[1]);
          String s = Temp[0].toString();
   ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1,array);
   lv_child.setAdapter(adapter);
   //here you can work with your list
}

But I am getting exception android.view.viewrootimpl$calledfromwrongthreadexception

Kindly suggest me, waiting for reply.

Thanks

Answer 1

Try to use AsyncTask instead to Thread for get data from server :

   public void fetchJSONChild(final GetChildList callBack){

        new AsyncTask<Void,Void,List<String>>(){
            @Override
            protected List<String> doInBackground(Void... params) {
                List<String> child = new ArrayList<String>();
                try {
                    URL url = new URL("http://192.168.x.xx:xxxx/childform_list/0.0.0.0/8069/new_db/admin/123456");
                    HttpURLConnection conn = (HttpURLConnection) url.openConnection();
                    conn.setReadTimeout(30000 /* milliseconds */);
                    conn.setConnectTimeout(50000 /* milliseconds */);
                    conn.setRequestMethod("GET");
                    //conn.setRequestProperty("User-Agent", "GYUserAgentAndroid");
                    conn.setRequestProperty("Content-Type", "application/json");
                    conn.setDoInput(true);
                    //conn.setUseCaches (false);
                    // Starts the query
                    if (Build.VERSION.SDK != null && Build.VERSION.SDK_INT > 13) {

                        conn.setRequestProperty("Connection", "close");
                    }
                    conn.connect();

                    System.out.println("Before url.openStream()");
                    InputStream stream = conn.getInputStream();//.openStream();
                    System.out.println("After url.openStream()");
                    String data = convertStreamToString(stream);
                    // for examole data = "1,2,3";

                    child.addAll(Arrays.asList(data.split(",")));
                    readAndParseJSON(data);
                    stream.close();
                }catch (Exception e){
                    e.printStackTrace();
                }
                return child;
            }

            @Override
            protected void onPostExecute(List<String> child) {
                super.onPostExecute(child);
                callBack.onGetChildList(child);
            }
        }.execute();

    }

Answer 2

The issue is that you're trying to invoke onGetChildList(List<String> list) method from the new Thread . You can't do that, because all the work that needs to be done on your UI has to performed from the main thread (sometimes called UI thread). You can read more about it here .
I suggest you create new AsyncTask here and move all your code inside the run method except for the last line to its doInBackground() method. The latest line needs to be moved inside the AsyncTask#onPostExecute method, so the whole structure looks like this:

    new AsyncTask<Void,Void,List<String>>(){
        @Override
        protected List<String> doInBackground(Void... params) {
            List<String> child = new ArrayList<String>();
            try {
                // code omitted for brevity
            }catch (Exception e){
                e.printStackTrace();
            }
            return child;
        }

        @Override
        protected void onPostExecute(List<String> child) {
            super.onPostExecute(child);
            callBack.onGetChildList(child);
        }
    }.execute();

It will work because doInBackground() method executes inside the background thread and when this method finishes, AsyncTask passes its result to the onPostExecute which is being executed on the UI thread. AsyncTask was made specifically for this kind of tasks - do something in background, then update UI with the results.