E/AndroidRuntime: FATAL EXCEPTION: AsyncTask #1 java.lang.RuntimeException: An error occured while executing doInBackground()

Question

I am a beginner in programming and I just want to create an app that display some markers on map using some coordinates from a database( hosted by 000webhost), using PHP and JSON.The map is working, but there are no markers. Please help me because I really cannot figure it out.

This is the error message i get:

E/AndroidRuntime: FATAL EXCEPTION: AsyncTask #1
                                                   Process: com.kid.compaq.licenta, PID: 24949
                                                   java.lang.RuntimeException: An error occured while executing doInBackground()
                                                       at android.os.AsyncTask$3.done(AsyncTask.java:304)
                                                       at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:355)
                                                       at java.util.concurrent.FutureTask.setException(FutureTask.java:222)
                                                       at java.util.concurrent.FutureTask.run(FutureTask.java:242)
                                                       at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
                                                       at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
                                                       at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
                                                       at java.lang.Thread.run(Thread.java:818)
                                                    Caused by: java.lang.IllegalStateException: Not on the main thread
                                                       at maps.f.g.b(Unknown Source)
                                                       at maps.z.D.a(Unknown Source)
                                                       at maps.ag.t.a(Unknown Source)
                                                       at uz.onTransact(:com.google.android.gms.DynamiteModulesB:167)
                                                       at android.os.Binder.transact(Binder.java:385)
                                                       at com.google.android.gms.maps.internal.IGoogleMapDelegate$zza$zza.addMarker(Unknown Source)
                                                       at com.google.android.gms.maps.GoogleMap.addMarker(Unknown Source)
                                                       at com.kid.compaq.licenta.MapsActivity$MarkerTask.doInBackground(MapsActivity.java:106)
                                                       at com.kid.compaq.licenta.MapsActivity$MarkerTask.doInBackground(MapsActivity.java:62)
                                                       at android.os.AsyncTask$2.call(AsyncTask.java:292)
                                                       at java.util.concurrent.FutureTask.run(FutureTask.java:237)
                                                       at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231) 
                                                       at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112) 
                                                       at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587) 
                                                       at java.lang.Thread.run(Thread.java:818) 
05-28 19:22:28.324 731-919/? E/InputDispatcher: channel 'd1579c5 com.kid.compaq.licenta/com.kid.compaq.licenta.MapsActivity (server)' ~ Channel is unrecoverably broken and will be disposed!
05-28 19:23:01.289 731-1342/? E/Sensors: handleToDriver handle(0)
05-28 19:23:01.290 731-1342/? E/Sensors: handleToDriver handle(0)
05-28 19:23:01.290 731-1342/? E/Sensors: new setDelay handle(0),ns(20000000)m, error(0), index(2)
05-28 19:23:01.299 731-939/? E/WifiStateMachine:  DisconnectedState (when=0 what=131143 arg1=10009 arg2=682) CMD_START_SCAN 10009 682 ic=0 proc(ms):0 dur:692 cnt=2252 rssi=-64 f=-1 sc=0 link=-1 tx=0,0, 0,0, 0,0  rx=0,0 fiv=20000 [on:0 tx:0 rx:0 period:121028] from screen [on:0 period:-131266637]
05-28 19:23:01.299 731-939/? E/WifiStateMachine:  ConnectModeState (when=-1ms what=131143 arg1=10009 arg2=682) CMD_START_SCAN 10009 682 ic=0 proc(ms):1 dur:692 cnt=2252 rssi=-64 f=-1 sc=0 link=-1 tx=0,0, 0,0, 0,0  rx=0,0 fiv=20000 [on:0 tx:0 rx:0 period:0] from screen [on:0 period:-131266637]
05-28 19:23:01.300 731-939/? E/WifiStateMachine:  DriverStartedState (when=-2ms what=131143 arg1=10009 arg2=682) CMD_START_SCAN 10009 682 ic=0 proc(ms):2 dur:692 cnt=2252 rssi=-64 f=-1 sc=0 link=-1 tx=0,0, 0,0, 0,0  rx=0,0 fiv=20000 [on:0 tx:0 rx:0 period:1] from screen [on:0 period:-131266636]
05-28 19:23:01.300 731-939/? E/WifiStateMachine: stopReconnectWifi Wfd=false StopScan=false mDontReconnectAndScan=false
05-28 19:23:01.302 731-939/? E/WifiStateMachine: [1.464.452.581.302 ms] noteScanStartWorkSource{10009} uid 10009
05-28 19:23:01.304 731-10206/? E/WifiMonitor: handleEvent unknown: 15  CTRL-EVENT-SCAN-STARTED 
05-28 19:23:01.322 1716-1792/? E/CellLocation: create GsmCellLocation
05-28 19:23:01.358 1716-1792/? E/CellLocation: create GsmCellLocation
05-28 19:23:01.415 1716-25019/? E/MPlugin: Unsupported class: com.mediatek.common.telephony.IOnlyOwnerSimSupport

MapsActivity:

import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
import android.util.Log;

import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.OnMapReadyCallback;
import com.google.android.gms.maps.SupportMapFragment;
import com.google.android.gms.maps.model.BitmapDescriptorFactory;
import com.google.android.gms.maps.model.LatLng;
import com.google.android.gms.maps.model.MarkerOptions;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;

public class MapsActivity extends FragmentActivity implements OnMapReadyCallback {

    HttpURLConnection urlConnection= null;
    private GoogleMap mMap;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_maps);
        // Obtain the SupportMapFragment and get notified when the map is ready to be used.
        SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager()
                .findFragmentById(R.id.map);
        mapFragment.getMapAsync(this);
        new MarkerTask().execute();
    }


    /**
     * Manipulates the map once available.
     * This callback is triggered when the map is ready to be used.
     * This is where we can add markers or lines, add listeners or move the camera. In this case,
     * we just add a marker near Sydney, Australia.
     * If Google Play services is not installed on the device, the user will be prompted to install
     * it inside the SupportMapFragment. This method will only be triggered once the user has
     * installed Google Play services and returned to the app.
     */
    @Override
    public void onMapReady(GoogleMap googleMap) {
        mMap = googleMap;
        mMap.getUiSettings().isCompassEnabled();
        mMap.getUiSettings().setZoomControlsEnabled(true);
        mMap.getUiSettings().setScrollGesturesEnabled(true);
        mMap.getUiSettings().setMapToolbarEnabled(true);


    }

    class MarkerTask extends AsyncTask<Void, String, Void> {



        @Override
        protected void onPreExecute() {
            super.onPreExecute();
        }

        @Override
        protected Void doInBackground(Void... params) {

            InputStream is = null;
            String result="";
            try {
                URL url = new URL("http://catcat.netne.net/get_mark.php");
                urlConnection = (HttpURLConnection) url.openConnection();
                urlConnection.connect();
                is = urlConnection.getInputStream();
//2 sec, tel
            } catch (Exception e) {
                Log.e("URL connection", e.toString());
            }
            try{
                BufferedReader reader = new BufferedReader(new InputStreamReader(is,"utf-8"));
                String line= null;
                while( (line= reader.readLine())!=null){
                    result +=line;
                }
                is.close();
            }
            catch (Exception e){
                e.printStackTrace();
            }
            try{
                JSONArray jsonArray = new JSONArray(result);
                for (int i = 0; i < jsonArray.length(); i++) {
                    JSONObject jsonObj = jsonArray.getJSONObject(i);

                    LatLng latLng = new LatLng(jsonObj.getJSONArray("latlng").getDouble(0),
                            jsonObj.getJSONArray("latlng").getDouble(1));


                    // Create a marker for each station in the JSON data.
                    mMap.addMarker(new MarkerOptions()
                            .icon(BitmapDescriptorFactory.defaultMarker(BitmapDescriptorFactory.HUE_BLUE))
                            .title(jsonObj.getString("nume"))
                            .position(latLng));
                }
            } catch (JSONException e) {
                e.printStackTrace();
            }


            return null;

        }
            // Executed after the complete execution of doInBackground() method
            @Override
            protected void onPostExecute (Void result){


            }

    }
}

php file:

<?php



@$dbhandle = mysql_connect($host,$user,$pass)or die("Unable to connect to MySQL");

$selected = mysql_select_db($db,$dbhandle)or die("Could not select licenta");


    $sql="SELECT id_st, nume, CONCAT_WS(\",\",lat, lng) AS latlng FROM statii";
    $result = mysql_query($sql);
    $response= array();
    while($row= mysql_fetch_assoc($result)){

        $response[]=array(
                            'nume'          => $row['nume'],
                            'latlng'        => explode(',', $row['latlng']),
                            'id_st'         => $row['id_st']
                            );
    }

//$bd_json = json_encode($response);
echo json_encode($response);
exit();

?>

Json response:

[{
    "nume": "Merge in sfarsit",
    "latlng": ["45.659721", "25.606859"],
    "id_st": "5"
}, {
    "nume": "Memo Cantina",
    "latlng": ["45.655075", "25.581560"],
    "id_st": "6"
}]

Answer 1

One issue that I see is that in the code below you are adding a marker to the Google Map (on UI thread) from the background thread:

// Create a marker for each station in the JSON data.
                mMap.addMarker(new MarkerOptions()
                        .icon(BitmapDescriptorFactory.defaultMarker(BitmapDescriptorFactory.HUE_BLUE))
                        .title(jsonObj.getString("nume"))
                        .position(latLng));

Either create an entire set of markers built in the loop first, maybe in a list, and then pass the list to the onPostExecute at the end where you would add them to the map there, or post each marker using the onProgressUpdate method like:

// Create a marker for each station in the JSON data.
mMarker = new MarkerOptions().icon(BitmapDescriptorFactory.defaultMarker(BitmapDescriptorFactory.HUE_BLUE))
                        .title(jsonObj.getString("nume"))
                        .position(latLng);
onProgressUpdate(mMarker);

Make sure to add:

MarkerOptions mMarker;

below this line:

private GoogleMap mMap;

And then override the OnProgressUpdate method:

protected void onProgressUpdate(MarkerOptions marker) {
     mMap.addMarker(marker);
 }

Don't forget to change

class MarkerTask extends AsyncTask<Void, String, Void> {

to

class MarkerTask extends AsyncTask<Void, MarkerOptions, Void> {

While this might help you get past this issue, you really should review the AsyncTask class and get yourself familiar it.

Good luck!