Android Lazy Loading images and text in listview from http json data

In this article, we will create an Android application containing listview with images and text. The listview items are loaded from a remote http json object. The images and text are loaded in listview as they get downloaded to the device.

The whole application can be divided in to three different processes as follows :

1. Download JSON data from http url ( DownloadTask )

2. Parse JSON data and populate listview with text ( ListViewLoaderTask )

3. Download image from http server and populate listview with images at appropriate positions ( ImageLoaderTask)

This article is an extension to the article titled “ListView with Images and Text using Simple Adapter in Android“.

This application is developed in Eclipse ( 4.2.0 ) with ADT plugin ( 20.0.3 ) and Android SDK ( R20.0.3 )

1. Create a new Android application project namely “ListViewWithJSONFromURL”

Figure 1 : New Androd Application Project

2. Design application launcher icon

Figure 2 : Design Application launcher icon

3. Create a blank activity to define the class MainActivity

Figure 3 : Create a blank activity

4. Enter MainActivity class details

Figure 4 : Enter MainActivity Details

5. Delete the Android support library, if exists

By default Eclipse ( 4.2.0) adds Android Support Library to  Android application project. For this application, we don’t need to use this support library. So the library file libs/android-support-v4.jar may be removed manually via ProjectExplorer by simply right click on the file and then clicking the menu item “delete”.

6. Create a folder namely “drawable” under the folder “res”

7. Download the given below image to the folder res/drawable

8. Update the file res/values/strings.xml

<resources>
    <string name="app_name">ListViewWithJSONFromURL</string>
    <string name="hello_world">Hello world!</string>
    <string name="menu_settings">Settings</string>
    <string name="title_activity_main">ListView with JSON From URL</string>
    <string name="str_iv_flag">Flag</string>
</resources>

9. Create a custom layout for the listview in res/layout/lv_layout.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

    <TextView
        android:id="@+id/tv_country"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:textSize="20dp"
        android:textStyle="bold" />

    <ImageView
        android:id="@+id/iv_flag"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@id/tv_country"
        android:layout_centerVertical="true"
        android:padding="5dp"
        android:contentDescription="@string/str_iv_flag" />

    <TextView
        android:id="@+id/tv_country_details"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_toRightOf="@id/iv_flag"
        android:layout_below="@id/tv_country"  />

</RelativeLayout>

10. Update the layout activity_main in the file res/layout/activity_main.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

    <ListView
        android:id="@+id/lv_countries"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        tools:context=".MainActivity" />
</RelativeLayout>

11. Create a JSON parser class in the file src/in/wptrafficanalyzer/listviewwithjsonfromurl/CountryJSONParser.java

package in.wptrafficanalyzer.listviewwithjsonfromurl;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;

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

/** A class to parse json data */
public class CountryJSONParser {

    // Receives a JSONObject and returns a list
    public List<HashMap<String,Object>> parse(JSONObject jObject){

        JSONArray jCountries = null;
        try {
            // Retrieves all the elements in the 'countries' array
            jCountries = jObject.getJSONArray("countries");
        } catch (JSONException e) {
            e.printStackTrace();
        }

        // Invoking getCountries with the array of json object
        // where each json object represent a country
        return getCountries(jCountries);
    }

    private List<HashMap<String, Object>> getCountries(JSONArray jCountries){
        int countryCount = jCountries.length();
        List<HashMap<String, Object>> countryList = new ArrayList<HashMap<String,Object>>();
        HashMap<String, Object> country = null;

        // Taking each country, parses and adds to list object
        for(int i=0; i<countryCount;i++){
            try {
                // Call getCountry with country JSON object to parse the country
                country = getCountry((JSONObject)jCountries.get(i));
                countryList.add(country);

            } catch (JSONException e) {
                e.printStackTrace();
            }
        }

        return countryList;
    }

    // Parsing the Country JSON object
    private HashMap<String, Object> getCountry(JSONObject jCountry){

        HashMap<String, Object> country = new HashMap<String, Object>();
        String countryName = "";
        String flag="";
        String language = "";
        String capital = "";
        String currencyCode = "";
        String currencyName = "";

        try {
            countryName = jCountry.getString("countryname");
            flag = jCountry.getString("flag");
            language = jCountry.getString("language");
            capital = jCountry.getString("capital");
            currencyCode = jCountry.getJSONObject("currency").getString("code");
            currencyName = jCountry.getJSONObject("currency").getString("currencyname");

            String details =        "Language : " + language + "\n" +
                                "Capital : " + capital + "\n" +
                                "Currency : " + currencyName + "(" + currencyCode + ")";

            country.put("country", countryName);
            country.put("flag", R.drawable.blank);
            country.put("flag_path", flag);
            country.put("details", details);

        } catch (JSONException e) {
            e.printStackTrace();
        }
        return country;
    }
}

12. Update the class MainActivity in the file src/in/wptrafficanalyzer/listviewwithjsonfromurl/MainActivity.java

package in.wptrafficanalyzer.listviewwithjsonfromurl;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.HashMap;
import java.util.List;

import org.json.JSONObject;

import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.widget.ListView;
import android.widget.SimpleAdapter;

public class MainActivity extends Activity {

    ListView mListView;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // URL to the JSON data
        String strUrl = "http://wptrafficanalyzer.in/p/demo1/first.php/countries";

        // Creating a new non-ui thread task to download json data
        DownloadTask downloadTask = new DownloadTask();

        // Starting the download process
        downloadTask.execute(strUrl);

        // Getting a reference to ListView of activity_main
        mListView = (ListView) findViewById(R.id.lv_countries);

    }

    /** A method to download json data from url */
    private String downloadUrl(String strUrl) throws IOException{
        String data = "";
        InputStream iStream = null;
        try{
            URL url = new URL(strUrl);

            // Creating an http connection to communicate with url
            HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();

            // Connecting to url
            urlConnection.connect();

            // Reading data from url
            iStream = urlConnection.getInputStream();

            BufferedReader br = new BufferedReader(new InputStreamReader(iStream));

            StringBuffer sb  = new StringBuffer();

            String line = "";
            while( ( line = br.readLine())  != null){
                sb.append(line);
            }

            data = sb.toString();

            br.close();

        }catch(Exception e){
            Log.d("Exception while downloading url", e.toString());
        }finally{
            iStream.close();
        }

        return data;
    }

    /** AsyncTask to download json data */
    private class DownloadTask extends AsyncTask<String, Integer, String>{
        String data = null;
        @Override
        protected String doInBackground(String... url) {
            try{
                data = downloadUrl(url[0]);
            }catch(Exception e){
                Log.d("Background Task",e.toString());
            }
            return data;
        }

        @Override
        protected void onPostExecute(String result) {

            // The parsing of the xml data is done in a non-ui thread
            ListViewLoaderTask listViewLoaderTask = new ListViewLoaderTask();

            // Start parsing xml data
            listViewLoaderTask.execute(result);
        }
    }

    /** AsyncTask to parse json data and load ListView */
    private class ListViewLoaderTask extends AsyncTask<String, Void, SimpleAdapter>{

        JSONObject jObject;
        // Doing the parsing of xml data in a non-ui thread
        @Override
        protected SimpleAdapter doInBackground(String... strJson) {
            try{
                jObject = new JSONObject(strJson[0]);
                CountryJSONParser countryJsonParser = new CountryJSONParser();
                countryJsonParser.parse(jObject);
            }catch(Exception e){
                Log.d("JSON Exception1",e.toString());
            }

            // Instantiating json parser class
            CountryJSONParser countryJsonParser = new CountryJSONParser();

            // A list object to store the parsed countries list
            List<HashMap<String, Object>> countries = null;

            try{
                // Getting the parsed data as a List construct
                countries = countryJsonParser.parse(jObject);
            }catch(Exception e){
                Log.d("Exception",e.toString());
            }

            // Keys used in Hashmap
            String[] from = { "country","flag","details"};

            // Ids of views in listview_layout
            int[] to = { R.id.tv_country,R.id.iv_flag,R.id.tv_country_details};

            // Instantiating an adapter to store each items
            // R.layout.listview_layout defines the layout of each item
            SimpleAdapter adapter = new SimpleAdapter(getBaseContext(), countries, R.layout.lv_layout, from, to);

            return adapter;
        }

        /** Invoked by the Android on "doInBackground" is executed */
        @Override
        protected void onPostExecute(SimpleAdapter adapter) {

            // Setting adapter for the listview
            mListView.setAdapter(adapter);

            for(int i=0;i<adapter.getCount();i++){
                HashMap<String, Object> hm = (HashMap<String, Object>) adapter.getItem(i);
                String imgUrl = (String) hm.get("flag_path");
                ImageLoaderTask imageLoaderTask = new ImageLoaderTask();

                HashMap<String, Object> hmDownload = new HashMap<String, Object>();
                hm.put("flag_path",imgUrl);
                hm.put("position", i);

                // Starting ImageLoaderTask to download and populate image in the listview
                imageLoaderTask.execute(hm);
            }
        }
    }

    /** AsyncTask to download and load an image in ListView */
    private class ImageLoaderTask extends AsyncTask<HashMap<String, Object>, Void, HashMap<String, Object>>{

        @Override
        protected HashMap<String, Object> doInBackground(HashMap<String, Object>... hm) {

            InputStream iStream=null;
            String im
            gUrl = (String) hm[0].get("flag_path");
            int position = (Integer) hm[0].get("position");

            URL url;
            try {
                url = new URL(imgUrl);

                // Creating an http connection to communicate with url
                HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();

                // Connecting to url
                urlConnection.connect();

                // Reading data from url
                iStream = urlConnection.getInputStream();

                // Getting Caching directory
                File cacheDirectory = getBaseContext().getCacheDir();

                // Temporary file to store the downloaded image
                File tmpFile = new File(cacheDirectory.getPath() + "/wpta_"+position+".png");

                // The FileOutputStream to the temporary file
                FileOutputStream fOutStream = new FileOutputStream(tmpFile);

                // Creating a bitmap from the downloaded inputstream
                Bitmap b = BitmapFactory.decodeStream(iStream);

                // Writing the bitmap to the temporary file as png file
                b.compress(Bitmap.CompressFormat.PNG,100, fOutStream);

                // Flush the FileOutputStream
                fOutStream.flush();

               //Close the FileOutputStream
               fOutStream.close();

                // Create a hashmap object to store image path and its position in the listview
                HashMap<String, Object> hmBitmap = new HashMap<String, Object>();

                // Storing the path to the temporary image file
                hmBitmap.put("flag",tmpFile.getPath());

                // Storing the position of the image in the listview
                hmBitmap.put("position",position);

                // Returning the HashMap object containing the image path and position
                return hmBitmap;

            }catch (Exception e) {
                e.printStackTrace();
            }
            return null;
        }

        @Override
        protected void onPostExecute(HashMap<String, Object> result) {
            // Getting the path to the downloaded image
            String path = (String) result.get("flag");

            // Getting the position of the downloaded image
            int position = (Integer) result.get("position");

            // Getting adapter of the listview
            SimpleAdapter adapter = (SimpleAdapter ) mListView.getAdapter();

            // Getting the hashmap object at the specified position of the listview
            HashMap<String, Object> hm = (HashMap<String, Object>) adapter.getItem(position);

            // Overwriting the existing path in the adapter
            hm.put("flag",path);

            // Noticing listview about the dataset changes
            adapter.notifyDataSetChanged();
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.activity_main, menu);
        return true;
    }
}

13. Update AndroidManifest.xml to provide Internet access permission for this application

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="in.wptrafficanalyzer.listviewwithjsonfromurl"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="4"
        android:targetSdkVersion="15" />

    <uses-permission android:name="android.permission.INTERNET"/>

    <application
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name=".MainActivity"
            android:label="@string/title_activity_main" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

14. Screenshot of the application

Figure 5 : Loading Images and Text in ListView

15. Download

16. Reference

http://developer.android.com/guide/index.html

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Tags: asynchronous, ASyncTask, cache directory, HttpUrlConnection, image, ImageVIew, json, lazy loading, listview, SimpleAdapter