Load Flickr images in background thread

In the exercise "Display Flickr photos in Gallery using BaseAdapter", the Flickr photos are loaded in foreground thread. If it take long time to load photos from Flickr server, the app will be killed by Android OS. In this exercise, the job will be moved to a background thread, and a ProgressDialog will be displayed to user. (For example of using background thread and ProgressDialog, refer the post "ProgressDialog + Thread").

package com.exercise.AndroidFlickr;

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

import org.apache.http.HttpEntity;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import android.app.Activity;
import android.app.ProgressDialog;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.View;
import android.view.ViewGroup;
import android.view.ViewGroup.LayoutParams;
import android.widget.BaseAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Gallery;
import android.widget.ImageView;
import android.widget.Toast;

public class AndroidFlickrActivity extends Activity {

ProgressDialog progressDialog;
BackgroundThread backgroundThread;

public class FlickrImage {
   String Id;
   String Owner;
   String Secret;
   String Server;
   String Farm;
   String Title;
  
   Bitmap FlickrBitmap;
  
   FlickrImage(String _Id, String _Owner, String _Secret,
     String _Server, String _Farm, String _Title){
    Id = _Id;
       Owner = _Owner;
       Secret = _Secret;
       Server = _Server;
       Farm = _Farm;
       Title = _Title;
      
       FlickrBitmap = preloadBitmap();
   }
  
   private Bitmap preloadBitmap(){
    Bitmap bm= null;
      
       String FlickrPhotoPath =
         "http://farm" + Farm + ".static.flickr.com/"
         + Server + "/" + Id + "_" + Secret + "_m.jpg";
      
       URL FlickrPhotoUrl = null;
      
       try {
     FlickrPhotoUrl = new URL(FlickrPhotoPath);
    
     HttpURLConnection httpConnection
      = (HttpURLConnection) FlickrPhotoUrl.openConnection();
     httpConnection.setDoInput(true);
     httpConnection.connect();
     InputStream inputStream = httpConnection.getInputStream();
     bm = BitmapFactory.decodeStream(inputStream);
    
    } catch (MalformedURLException e) {
     // TODO Auto-generated catch block
     e.printStackTrace();
    } catch (IOException e) {
     // TODO Auto-generated catch block
     e.printStackTrace();
    }
      
       return bm;
   }
  
   public Bitmap getBitmap(){
    return FlickrBitmap;
   }

}

class FlickrAdapter extends BaseAdapter{
 private Context context;
 private FlickrImage[] FlickrAdapterImage;;

 FlickrAdapter(Context c, FlickrImage[] fImage){
  context = c;
  FlickrAdapterImage = fImage;
 }

 public int getCount() {
  // TODO Auto-generated method stub
  return FlickrAdapterImage.length;
 }

 public Object getItem(int position) {
  // TODO Auto-generated method stub
  return FlickrAdapterImage[position];
 }

 public long getItemId(int position) {
  // TODO Auto-generated method stub
  return position;
 }

 public View getView(int position, View convertView, ViewGroup parent) {
  // TODO Auto-generated method stub
  ImageView image;
  if (convertView == null) {
   image = new ImageView(context);
   image.setLayoutParams(new Gallery.LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT));
   image.setScaleType(ImageView.ScaleType.CENTER_CROP);
   image.setPadding(8, 8, 8, 8);  
  } else {
   image = (ImageView) convertView;  
  }

  image.setImageBitmap(FlickrAdapterImage[position].getBitmap());
    
     return image;
 }

}

FlickrImage[] myFlickrImage;

/*
 * FlickrQuery = FlickrQuery_url
 * + FlickrQuery_per_page
 * + FlickrQuery_nojsoncallback
 * + FlickrQuery_format
 * + FlickrQuery_tag + q
 * + FlickrQuery_key + FlickrApiKey
 */

String FlickrQuery_url = "http://api.flickr.com/services/rest/?method=flickr.photos.search";
String FlickrQuery_per_page = "&per_page=10";
String FlickrQuery_nojsoncallback = "&nojsoncallback=1";
String FlickrQuery_format = "&format=json";
String FlickrQuery_tag = "&tags=";
String FlickrQuery_key = "&api_key=";

// Apply your Flickr API:
// www.flickr.com/services/apps/create/apply/?
String FlickrApiKey = "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx";

//final String DEFAULT_SEARCH = "Bill_Gate";
final String DEFAULT_SEARCH = "new_york";

EditText searchText;
  Button searchButton;

  Gallery photoBar;

  Bitmap bmFlickr;

  /** Called when the activity is first created. */
  @Override
  public void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.main);
    
      searchText = (EditText)findViewById(R.id.searchtext);
      searchText.setText(DEFAULT_SEARCH);
      searchButton = (Button)findViewById(R.id.searchbutton);
    
      photoBar = (Gallery)findViewById(R.id.photobar);
    
      searchButton.setOnClickListener(searchButtonOnClickListener);
  }

  private Button.OnClickListener searchButtonOnClickListener
  = new Button.OnClickListener(){

 public void onClick(View arg0) {
  // TODO Auto-generated method stub
  progressDialog = ProgressDialog.show(AndroidFlickrActivity.this,
                "ProgressDialog", "Wait!");
      
        backgroundThread = new BackgroundThread();
        backgroundThread.setRunning(true);
        backgroundThread.start();
 
 
 

 }};


  private String QueryFlickr(String q){
  
   String qResult = null;
  
   String qString =
     FlickrQuery_url
     + FlickrQuery_per_page
     + FlickrQuery_nojsoncallback
     + FlickrQuery_format
     + FlickrQuery_tag + q
     + FlickrQuery_key + FlickrApiKey;
  
   HttpClient httpClient = new DefaultHttpClient();
      HttpGet httpGet = new HttpGet(qString);
    
      try {
  HttpEntity httpEntity = httpClient.execute(httpGet).getEntity();
 
  if (httpEntity != null){
   InputStream inputStream = httpEntity.getContent();
   Reader in = new InputStreamReader(inputStream);
   BufferedReader bufferedreader = new BufferedReader(in);
   StringBuilder stringBuilder = new StringBuilder();
  
   String stringReadLine = null;
  
   while ((stringReadLine = bufferedreader.readLine()) != null) {
    stringBuilder.append(stringReadLine + "\n");
    }
  
   qResult = stringBuilder.toString();
   inputStream.close();
  }
 
 } catch (ClientProtocolException e) {
  // TODO Auto-generated catch block
  e.printStackTrace();
 } catch (IOException e) {
  // TODO Auto-generated catch block
  e.printStackTrace();
 }
    
      return qResult;
  }

  private FlickrImage[] ParseJSON(String json){

   FlickrImage[] flickrImage = null;
  
   bmFlickr = null;
   String flickrId;
   String flickrOwner;
   String flickrSecret;
   String flickrServer;
   String flickrFarm;
   String flickrTitle;
  
   try {
  JSONObject JsonObject = new JSONObject(json);
  JSONObject Json_photos = JsonObject.getJSONObject("photos");
  JSONArray JsonArray_photo = Json_photos.getJSONArray("photo");
 
  flickrImage = new FlickrImage[JsonArray_photo.length()];
  for (int i = 0; i < JsonArray_photo.length(); i++){
   JSONObject FlickrPhoto = JsonArray_photo.getJSONObject(i);
   flickrId = FlickrPhoto.getString("id");
   flickrOwner = FlickrPhoto.getString("owner");
   flickrSecret = FlickrPhoto.getString("secret");
   flickrServer = FlickrPhoto.getString("server");
   flickrFarm = FlickrPhoto.getString("farm");
   flickrTitle = FlickrPhoto.getString("title");
   flickrImage[i] = new FlickrImage(flickrId, flickrOwner, flickrSecret,
     flickrServer, flickrFarm, flickrTitle);
  }
 
 } catch (JSONException e) {
  // TODO Auto-generated catch block
  e.printStackTrace();
 }
  
   return flickrImage;
  }

  public class BackgroundThread extends Thread{
   volatile boolean running = false;
   int cnt;
  
   void setRunning(boolean b){
    running = b;
    cnt = 10;
   }

 @Override
 public void run() {
  // TODO Auto-generated method stub
  String searchQ = searchText.getText().toString();
  String searchResult = QueryFlickr(searchQ);
 
  myFlickrImage = ParseJSON(searchResult);
 
 
  handler.sendMessage(handler.obtainMessage());
 }
  }

  Handler handler = new Handler(){

 @Override
 public void handleMessage(Message msg) {
  // TODO Auto-generated method stub
 
  progressDialog.dismiss();
  photoBar.setAdapter(new FlickrAdapter(AndroidFlickrActivity.this, myFlickrImage));
  Toast.makeText(AndroidFlickrActivity.this,
    "Flickr images loaded", Toast.LENGTH_LONG).show();
 }
  
  };

}

Download the files.