Android: slow gallery view

Question

I 'm having a problem with my gallery, it's to slow and it lags. I 'm loading images from server with Image Adapter:

package com.example.ocenitaksi;

import java.io.IOException;
import java.io.InputStream;
import java.io.UnsupportedEncodingException;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLConnection;
import java.net.URLEncoder;

import org.apache.http.client.utils.URLEncodedUtils;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.TextView;



public class ImageAdapter extends BaseAdapter {
    private Context context;
    private final String[] mobileValues;

    public ImageAdapter(Context context, String[] mobileValues) {
        this.context = context;
        this.mobileValues = mobileValues;
    }

    public View getView(int position, View convertView, ViewGroup parent) {

        LayoutInflater inflater = (LayoutInflater) context
                .getSystemService(Context.LAYOUT_INFLATER_SERVICE);

        View gridView;

        if (convertView == null) {

            gridView = new View(context);

            // get layout from mobile.xml
            gridView = inflater.inflate(R.layout.mobile, null);


            // set image based on selected text
            ImageView imageView = (ImageView) gridView
                    .findViewById(R.id.grid_item_image);



            // ubacivanje slika za string


                String mobile = mobileValues[position];
                if (mobile.equals(MainActivity.imena[position])) {
                //imageView.setImageURI("http://24.media.tumblr.com/avatar_a400b4dbb80e_64.png");
                Bitmap bitmap=null;;

                mobile = mobile.replace(" ", "_");

                        bitmap = DownloadImage("http://android.yunews.net/images/"+mobile+".png");


                    imageView.setImageBitmap(bitmap);

                }


        } 
        else {
            gridView = (View) convertView;
        }

        return gridView;
    }

    @Override
    public int getCount() {
        return mobileValues.length;
    }

    @Override
    public Object getItem(int position) {
        return null;
    }

    @Override
    public long getItemId(int position) {
        return 0;
    }
    private InputStream OpenHttpConnection(String urlString) throws IOException {
        InputStream in = null;
        int response = -1;

        URL url = new URL(urlString);
        URLConnection conn = url.openConnection();

        if (!(conn instanceof HttpURLConnection))
            throw new IOException("Not an HTTP connection");

        try {
            HttpURLConnection httpConn = (HttpURLConnection) conn;
            httpConn.setAllowUserInteraction(false);
            httpConn.setInstanceFollowRedirects(true);
            httpConn.setRequestMethod("GET");
            httpConn.connect();
            response = httpConn.getResponseCode();
            if (response == HttpURLConnection.HTTP_OK) {
                in = httpConn.getInputStream();
            }
        } catch (Exception ex) {
            throw new IOException("Error connecting");
        }
        return in;
    }

    private Bitmap DownloadImage(String URL) {
        Bitmap bitmap = null;
        InputStream in = null;
        try {
            in = OpenHttpConnection(URL);
            bitmap = BitmapFactory.decodeStream(in);
            in.close();
        } catch (IOException e1) {
            // TODO Auto-generated catch block
            e1.printStackTrace();
        }
        return bitmap;
    }
}

and this is part of my main activity.

private class LongOperation extends AsyncTask<String, Void, String> 
    {
        protected void onPreExecute() 
        { 
            progressDialog = new ProgressDialog(MainActivity.this); 
            progressDialog.setTitle("Molimo sacekajte...");
            progressDialog.setMessage("Ucitavam taksi sluzbe...");
            progressDialog.setCancelable(true);
            progressDialog.show();
        }

        protected String doInBackground(String... params) 
        {

                niz = new JSONFunkcije().ListaSluzbi();

                imena= new String[niz.size()];
                Iterator<String> it= niz.iterator();
                for (int i=0;i<niz.size();i++)
                    imena[i]=it.next();
                slicice = new ImageAdapter(MainActivity.this, imena);


            return null;
        }
        protected void onPostExecute(String result) 
        {

            progressDialog.dismiss();

            runOnUiThread(new Runnable() {
                public void run() {
                    /**
                     * Updating parsed JSON data into ListView
                     * */
                    //Button dugme1 = (Button) findViewById(R.id.dugme1);

                    ///params.height = "50dpi";
                    //dugme1.setLayoutParams(new LinearLayout.LayoutParams(LayoutParams.MATCH_PARENT, 100));

                    Gallery gridView = (Gallery) findViewById(R.id.gallery1);

                    gridView.setAdapter(slicice);
                    //kraj ucitvanja

                    //gridView.setAdapter(adapter);
                    gridView.setOnItemClickListener(new OnItemClickListener() {
                        @Override
                        public void onItemClick(AdapterView<?> parent, View v,
                                int position, long id) {

                            // Sending image id to FullScreenActivity
                            Intent i = new Intent(getApplicationContext(), TaksiDetalji.class);
                            // passing array index
                            i.putExtra("id", imena[position]);
                            startActivity(i);
                        }
                    });

                }
            });
        System.gc();
        }
      }

I 'm calling LongOperation from OnCrate:

mytask = new LongOperation();
        mytask.execute(); 

Is something wrong with ImageAdapter? Too many calls, downloads? I tried to cache images but I failed.

Answer 1

From your code, I would say there are many reasons and because all these below reasons its running slow:

1. You haven't followed ViewHolder pattern. Read documentation also for Making ListView Scrolling Smooth
2. You haven't followed standard way of loading images (i.e. Cached images in local, load from local if its already cached)

Better you try any library available (Universal Image loader or any) on web to load images in your ListView.