import android.app.ProgressDialog;
    import android.content.Intent;
    import android.graphics.Bitmap;
    import android.graphics.BitmapFactory;
    import android.net.Uri;

import android.os.AsyncTask;
import android.os.Bundle;
import android.support.design.widget.NavigationView;
import android.support.v4.view.GravityCompat;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarDrawerToggle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;

import com.google.android.gms.appindexing.Action;
import com.google.android.gms.appindexing.AppIndex;
import com.google.android.gms.common.api.GoogleApiClient;

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

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;


//import com.example.nikos.map.MapsActivity;

public class MainActivity extends AppCompatActivity implements NavigationView.OnNavigationItemSelectedListener {

    /**
     * ATTENTION: This was auto-generated to implement the App Indexing API.
     * See https://g.co/AppIndexing/AndroidStudio for more information.
     */

    private String imagesJSON;

    private static final String JSON_ARRAY ="result";
    private static final String IMAGE_URL = "url";
    private JSONArray arrayImages= null;
    private int TRACK = 0;

    private static final String IMAGES_URL = "http://192.168.1.116/images.php";

    private Button buttonFetchImages;
    private Button buttonMoveNext;
    private Button buttonMovePrevious;
    private ImageView imageView;



    private GoogleApiClient client;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        imageView = (ImageView) findViewById(R.id.imageView2);

        buttonMoveNext = (Button) findViewById(R.id.buttonNext);
        buttonMovePrevious = (Button) findViewById(R.id.buttonPrev);
        getAllImages();

      /*  FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
        assert fab != null;
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                        .setAction("Action", null).show();
            }
        });
*/
        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
                this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
        drawer.setDrawerListener(toggle);
        toggle.syncState();

        NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
        navigationView.setNavigationItemSelectedListener(this);
        // ATTENTION: This was auto-generated to implement the App Indexing API.
        // See https://g.co/AppIndexing/AndroidStudio for more information.
        client = new GoogleApiClient.Builder(this).addApi(AppIndex.API).build();

    }

    private void extractJSON(){
        try {
            JSONObject jsonObject = new JSONObject(imagesJSON);
            arrayImages = jsonObject.getJSONArray(JSON_ARRAY);
        } catch (JSONException e) {
            e.printStackTrace();
        }
    }

    private void showImage(){
        try {
            JSONObject jsonObject = arrayImages.getJSONObject(TRACK);
            getImage(jsonObject.getString(IMAGE_URL));
        } catch (JSONException e) {
            e.printStackTrace();
        }
    }

    private void moveNext(){
        if(TRACK < arrayImages.length()){
            TRACK++;
            showImage();
        }
    }

    private void movePrevious(){
        if(TRACK>0){
            TRACK--;
            showImage();
        }
    }

    private void getAllImages() {
        class GetAllImages extends AsyncTask<String,Void,String> {
            ProgressDialog loading;
            @Override
            protected void onPreExecute() {
                super.onPreExecute();
                loading = ProgressDialog.show(MainActivity.this, "Fetching Data...","Please Wait...",true,true);
            }

            @Override
            protected void onPostExecute(String s) {
                super.onPostExecute(s);
                loading.dismiss();
                imagesJSON = s;
                extractJSON();
                showImage();
            }

            @Override
            protected String doInBackground(String... params) {
                String uri = params[0];
                BufferedReader bufferedReader;
                try {
                    URL url = new URL(uri);
                    HttpURLConnection con = (HttpURLConnection) url.openConnection();
                    StringBuilder sb = new StringBuilder();

                    bufferedReader = new BufferedReader(new InputStreamReader(con.getInputStream()));
                    String json;
                    while((json = bufferedReader.readLine())!= null){
                        sb.append(json+"n");
                    }

                    return sb.toString().trim();

                }catch(Exception e){
                    return null;
                }
            }
        }
        GetAllImages gai = new GetAllImages();
        gai.execute(IMAGES_URL);
    }

    private void getImage(String urlToImage){
        class GetImage extends AsyncTask<String,Void,Bitmap>{
            ProgressDialog loading;
            @Override
            protected Bitmap doInBackground(String... params) {
                URL url = null;

                Bitmap image = null;

                String urlToImage = params[0];
                try {
                    url = new URL(urlToImage);

                    image = BitmapFactory.decodeStream(url.openConnection().getInputStream());
                } catch (MalformedURLException e) {
                    e.printStackTrace();
                } catch (IOException e) {
                    e.printStackTrace();
                }
                return image;
            }

            @Override
            protected void onPreExecute() {
                super.onPreExecute();
                loading = ProgressDialog.show(MainActivity.this, "Downloading Image...", "Please wait...", true, true);
            }

            @Override
            protected void onPostExecute(Bitmap bitmap) {
                super.onPostExecute(bitmap);
                loading.dismiss();
                imageView.setImageBitmap(bitmap);
            }
        }
        GetImage gi = new GetImage();
        gi.execute(urlToImage);
    }


    public void onClick(View v) {
        if(v == buttonFetchImages) {
            getAllImages();
        }
        if(v == buttonMoveNext){
            moveNext();
        }
        if(v== buttonMovePrevious){
            movePrevious();
        }
    }



    @Override
    public void onBackPressed() {
        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        if (drawer.isDrawerOpen(GravityCompat.START)) {
            drawer.closeDrawer(GravityCompat.START);
        } else {
            super.onBackPressed();
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    @SuppressWarnings("StatementWithEmptyBody")
    @Override
    public boolean onNavigationItemSelected(MenuItem item) {
        // Handle navigation view item clicks here.
        int id = item.getItemId();

        if (id == R.id.login) {
            Intent intent3;
            intent3 = new Intent(MainActivity.this, LoginActivity.class);
            startActivity(intent3);
        } else if (id == R.id.map) {
            Intent intent2 = new Intent(MainActivity.this, MapsActivity.class);
            startActivity(intent2);

        } else if (id == R.id.search) {
            Intent intent6 = new Intent(MainActivity.this, SearchActivity.class);
            startActivity(intent6);
        } else if (id == R.id.leaf) {
            Intent intent5 = new Intent(MainActivity.this, LeafletActivity.class);
            startActivity(intent5);
        } else if (id == R.id.main) {

        } else if (id == R.id.information) {
            Intent intent4 = new Intent(MainActivity.this, InformationActivity.class);
            startActivity(intent4);
        } else if (id == R.id.lists) {

        }

        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        drawer.closeDrawer(GravityCompat.START);
        return true;
    }

    @Override
    public void onStart() {
        super.onStart();

        // ATTENTION: This was auto-generated to implement the App Indexing API.
        // See https://g.co/AppIndexing/AndroidStudio for more information.
        client.connect();
        Action viewAction = Action.newAction(
                Action.TYPE_VIEW, // TODO: choose an action type.
                "Main Page", // TODO: Define a title for the content shown.
                // TODO: If you have web page content that matches this app activity's content,
                // make sure this auto-generated web page URL is correct.
                // Otherwise, set the URL to null.
                Uri.parse("http://host/path"),
                // TODO: Make sure this auto-generated app deep link URI is correct.
                Uri.parse("android-app://com.example.nikos.papaapadakis/http/host/path")
        );
        AppIndex.AppIndexApi.start(client, viewAction);
    }

    @Override
    public void onStop() {
        super.onStop();

        // ATTENTION: This was auto-generated to implement the App Indexing API.
        // See https://g.co/AppIndexing/AndroidStudio for more information.
        Action viewAction = Action.newAction(
                Action.TYPE_VIEW, // TODO: choose an action type.
                "Main Page", // TODO: Define a title for the content shown.
                // TODO: If you have web page content that matches this app activity's content,
                // make sure this auto-generated web page URL is correct.
                // Otherwise, set the URL to null.
                Uri.parse("http://host/path"),
                // TODO: Make sure this auto-generated app deep link URI is correct.
                Uri.parse("android-app://com.example.nikos.papaapadakis/http/host/path")
        );
        AppIndex.AppIndexApi.end(client, viewAction);
        client.disconnect();

    }
}

and my php file

    <?php
$host="localhost"; //replace with database hostname
$username="root"; //replace with database username
$password=""; //replace with database password
$db_name="supermarket"; //replace with database name

$con=mysqli_connect("localhost", "root", "")or die("cannot connect");



mysqli_select_db($con,"supermarket")or die("cannot select DB");
    $sql = "select pid from deals";

 $res = mysqli_query($con,$sql);


 $result = array();

 $url = "http://192.168.1.116/images.php?pid=";
 while($row = mysqli_fetch_array($res)){
 array_push($result,array('url'=>$url.$row['pid']));
 }

print json_encode(array("result"=>$result));

 mysqli_close($con);
 ?>