Need Help in Downloading in Background Images in Android?

Question

I have an image view , i had written swiping , at that time of swiping,the images are downloading from Internet, so i thought i have to download the images in the background

Answer 1

You are probably over engineering this. I have implemented swiping with dynamically loading images and I just a use a simple utility class that does it all for me via static method call. Try this class:

package com.beget.consumer.util;

/*
 Licensed to the Apache Software Foundation (ASF) under one
or more contributor license agreements.  See the NOTICE file
distributed with this work for additional information
regarding copyright ownership.  The ASF licenses this file
to you 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.    
*/
import java.io.IOException;
import java.io.InputStream;
import java.lang.ref.WeakReference;
import java.net.MalformedURLException;
import java.util.HashMap;
import java.util.Map;

import org.apache.http.HttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;

import android.graphics.drawable.Drawable;
import android.os.Handler;
import android.os.Message;
import android.util.Log;
import android.widget.ImageView;

public class DrawableLoader {
    private final Map drawableMap;
    private WeakReference imageViewReference;

    public DrawableLoader() {
        drawableMap = new HashMap();
    }

    public Drawable fetchDrawable(String urlString) {
        if (drawableMap.containsKey(urlString)) {
            return drawableMap.get(urlString);
        }

        Log.d(this.getClass().getSimpleName(), "image url:" + urlString);
        try {
            InputStream is = fetch(urlString);
            Drawable drawable = Drawable.createFromStream(is, "src");
            drawableMap.put(urlString, drawable);
            Log.d(this.getClass().getSimpleName(), "got a thumbnail drawable: " + drawable.getBounds() + ", "
                    + drawable.getIntrinsicHeight() + "," + drawable.getIntrinsicWidth() + ", "
                    + drawable.getMinimumHeight() + "," + drawable.getMinimumWidth());
            return drawable;
        } catch (MalformedURLException e) {
            Log.e(this.getClass().getSimpleName(), "fetchDrawable failed", e);
            return null;
        } catch (IOException e) {
            Log.e(this.getClass().getSimpleName(), "fetchDrawable failed", e);
            return null;
        }
    }

    public void fetchDrawableOnThread(final String urlString, final ImageView imageView) {

        imageViewReference = new WeakReference(imageView);

        if (drawableMap.containsKey(urlString)) {
            imageViewReference.get().setImageDrawable(drawableMap.get(urlString));
        }

        final Handler handler = new Handler() {
            @Override
            public void handleMessage(Message message) {
                imageViewReference.get().setImageDrawable((Drawable) message.obj);
            }
        };

        Thread thread = new Thread() {
            @Override
            public void run() {
                //TODO : set imageView to a "pending" image
                Drawable drawable = fetchDrawable(urlString);
                Message message = handler.obtainMessage(1, drawable);
                handler.sendMessage(message);
            }
        };
        thread.start();
    }

    private InputStream fetch(String urlString) throws MalformedURLException, IOException {
        DefaultHttpClient httpClient = new DefaultHttpClient();
        HttpGet request = new HttpGet(urlString);
        HttpResponse response = httpClient.execute(request);
        return response.getEntity().getContent();
    }

}

This is all you need. Then when you need to load an image, you call:

fetchDrawableOnThread("http://path/to/your/image.jpg", yourImageViewReference);

That's it.
If you have an URL from a JSON object, parse the URL into your string so:
String url = jsonObj.getString("url"); Then call fetchDrawableOnThread(url, yourImageViewReference);