Android example source code file (ImageManager.java)

This example Android source code file (ImageManager.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Android by Example" ^TM.

Java - Android tags/keywords

android, arraylist, bufferedreader, content, handler, httpget, imagemanager, io, ioexception, jsonobject, net, network, networkthread, panoramioitem, string, stringbuilder, thumbnail_url, uri, util, weakreference

The ImageManager.java Android example source code

/*
 * Copyright (C) 2008 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.android.panoramio;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
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.content.Context;
import android.database.DataSetObserver;
import android.graphics.Bitmap;
import android.os.Handler;
import android.util.Log;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.lang.ref.WeakReference;
import java.net.URI;
import java.util.ArrayList;

/**
 * This class is responsible for downloading and parsing the search results for
 * a particular area. All of the work is done on a separate thread, and progress
 * is reported back through the DataSetObserver set in
 * {@link #addObserver(DataSetObserver). State is held in memory by in memory
 * maintained by a single instance of the ImageManager class.
 */
public class ImageManager {
   private static final String TAG = "Panoramio";
    
    /**
     * Base URL for Panoramio's web API
     */
    private static final String THUMBNAIL_URL = "//www.panoramio.com/map/get_panoramas.php?order=popularity&set=public&from=0&to=20&miny=%f&minx=%f&maxy=%f&maxx=%f&size=thumbnail";

    /**
     * Used to post results back to the UI thread
     */
    private Handler mHandler = new Handler();

    /**
     * Holds the single instance of a ImageManager that is shared by the process.
     */
    private static ImageManager sInstance;
    
    /**
     * Holds the images and related data that have been downloaded
     */
    private ArrayList<PanoramioItem> mImages = new ArrayList();
    
    /**
     * Observers interested in changes to the current search results
     */
    private ArrayList<WeakReference mObservers = 
            new ArrayList<WeakReference();
    
    /**
     * True if we are in the process of loading
     */
    private boolean mLoading;
    
    private Context mContext;
    
    /**
     * Key for an Intent extra. The value is the zoom level selected by the user.
     */
    public static final String ZOOM_EXTRA = "zoom";

    /**
     * Key for an Intent extra. The value is the latitude of the center of the search
     * area chosen by the user.
     */
    public static final String LATITUDE_E6_EXTRA = "latitudeE6";

    /**
     * Key for an Intent extra. The value is the latitude of the center of the search
     * area chosen by the user.
     */
    public static final String LONGITUDE_E6_EXTRA = "longitudeE6";
    

    /**
     * Key for an Intent extra. The value is an item to display
     */
    public static final String PANORAMIO_ITEM_EXTRA = "item";
    
    public static ImageManager getInstance(Context c) {
        if (sInstance == null) {
            sInstance = new ImageManager(c.getApplicationContext());
        }
        return sInstance;
    }
    
    private ImageManager(Context c) {
        mContext = c;
    }
    
    /**
     * @return True if we are still loading content
     */
    public boolean isLoading() {
        return mLoading;
    }
    
    /**
     * Clear all downloaded content
     */
    public void clear() {
        mImages.clear();   
        notifyObservers();
    }
    
    /**
     * Add an item to and notify observers of the change.
     * @param item The item to add
     */
    private void add(PanoramioItem item) {
        mImages.add(item);   
        notifyObservers();
    }
    
    /**
     * @return The number of items displayed so far
     */
    public int size() {
        return mImages.size();
    }

    /**
     * Gets the item at the specified position
     */
    public PanoramioItem get(int position) {
        return mImages.get(position);
    }
    
    /**
     * Adds an observer to be notified when the set of items held by this ImageManager changes.
     */
    public void addObserver(DataSetObserver observer) {
        WeakReference<DataSetObserver> obs = new WeakReference(observer);
        mObservers.add(obs);
    }
    
    /**
     * Load a new set of search results for the specified area.
     * 
     * @param minLong The minimum longitude for the search area
     * @param maxLong The maximum longitude for the search area
     * @param minLat The minimum latitude for the search area
     * @param maxLat The minimum latitude for the search area
     */
    public void load(float minLong, float maxLong, float minLat, float maxLat) {
        mLoading = true;
        new NetworkThread(minLong, maxLong, minLat, maxLat).start();
    }
    
    /**
     * Called when something changes in our data set. Cleans up any weak references that
     * are no longer valid along the way.
     */
    private void notifyObservers() {
        final ArrayList<WeakReference observers = mObservers;
        final int count = observers.size();
        for (int i = count - 1; i >= 0; i--) {
            WeakReference<DataSetObserver> weak = observers.get(i);
            DataSetObserver obs = weak.get();
            if (obs != null) {
                obs.onChanged();
            } else {
                observers.remove(i);
            }
        }
        
    }
    
    /**
     * This thread does the actual work of downloading and parsing data.
     *
     */
    private class NetworkThread extends Thread {

        private float mMinLong;
        private float mMaxLong;
        private float mMinLat;
        private float mMaxLat;

        public NetworkThread(float minLong, float maxLong, float minLat, float maxLat) {
            mMinLong = minLong;
            mMaxLong = maxLong;
            mMinLat = minLat;
            mMaxLat = maxLat;
        }

        @Override
        public void run() {
            
            String url = THUMBNAIL_URL;
            url = String.format(url, mMinLat, mMinLong, mMaxLat, mMaxLong);
            try {
                URI uri = new URI("http", url, null);
                HttpGet get = new HttpGet(uri);
                
                HttpClient client = new DefaultHttpClient();
                HttpResponse response = client.execute(get);
                HttpEntity entity = response.getEntity();
                String str = convertStreamToString(entity.getContent());
                JSONObject json = new JSONObject(str);
                parse(json);
            } catch (Exception e) {
                Log.e(TAG, e.toString());
            }
        }
        
        private void parse(JSONObject json) {
            try {
                JSONArray array = json.getJSONArray("photos");
                int count = array.length();
                for (int i = 0; i < count; i++) {
                    JSONObject obj = array.getJSONObject(i);

                    long id = obj.getLong("photo_id");
                    String title = obj.getString("photo_title");
                    String owner = obj.getString("owner_name");
                    String thumb = obj.getString("photo_file_url");
                    String ownerUrl = obj.getString("owner_url");
                    String photoUrl = obj.getString("photo_url");
                    double latitude = obj.getDouble("latitude");
                    double longitude = obj.getDouble("longitude");
                    Bitmap b = BitmapUtils.loadBitmap(thumb);
                    if (title == null) {
                        title = mContext.getString(R.string.untitled);
                    }

                    final PanoramioItem item = new PanoramioItem(id, thumb, b,
                            (int) (latitude * Panoramio.MILLION),
                            (int) (longitude * Panoramio.MILLION), title, owner,
                            ownerUrl, photoUrl);
                    final boolean done = i == count - 1;
                    mHandler.post(new Runnable() {
                        public void run() {
                            
                            sInstance.mLoading = !done;
                            sInstance.add(item);
                        }
                    });
                }
            } catch (JSONException e) {
                Log.e(TAG, e.toString());
            }
        }

        private String convertStreamToString(InputStream is) {
            BufferedReader reader = new BufferedReader(new InputStreamReader(is), 8*1024);
            StringBuilder sb = new StringBuilder();
     
            String line = null;
            try {
                while ((line = reader.readLine()) != null) {
                    sb.append(line + "\n");
                }
            } catch (IOException e) {
                e.printStackTrace();
            } finally {
                try {
                    is.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
     
            return sb.toString();
        }

    }
    
}