Android 异步获取网络图片并处理图片Out Of Memory 内存溢出问题

测试环境为Adnroid 2.1以上。

1：AndroidManifest.xml 权限配置：

添加互联网访问权限：

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

2.异步图片类 ImageDownloadTask 

import java.io.ByteArrayOutputStream;

import java.io.IOException;

import java.io.InputStream;

import java.net.MalformedURLException;

import java.net.URL;

import android.graphics.Bitmap;

import android.graphics.BitmapFactory;

import android.os.AsyncTask;

import android.widget.ImageView;





public class ImageDownloadTask extends AsyncTask<Object, Object, Bitmap> {

    private ImageView imageView = null;

    /***

     * 这里获取到手机的分辨率大小

     * */

    public  void setDisplayWidth(int width) {

        _displaywidth = width;

    }



    public  int getDisplayWidth() {

        return _displaywidth;

    }



    public  void setDisplayHeight(int height) {

        _displayheight = height;

    }



    public  int getDisplayHeight() {

        return _displayheight;

    }



    public  int getDisplayPixels() {

        return _displaypixels;

    }

    

    private  int _displaywidth = 480;

    private  int _displayheight = 800;

    private  int _displaypixels = _displaywidth * _displayheight;



    @Override

    protected Bitmap doInBackground(Object... params) {

        // TODO Auto-generated method stub

        Bitmap bmp = null;

        imageView = (ImageView) params[1];

        

        try {

            String url = (String) params[0];

            bmp = getBitmap(url, _displaypixels,true);

        } catch (Exception e) {

            

            return null;

        }

        return bmp;

    }



    protected void onPostExecute(Bitmap result) {

        if (imageView != null&&result!=null) {

            imageView.setImageBitmap(result);

            if (null != result && result.isRecycled() == false)

                System.gc();

        }

    }

    /**

     * 通过URL获得网上图片。如:http://www.xxxxxx.com/xx.jpg

     * */

    public Bitmap getBitmap(String url, int displaypixels, Boolean isBig) throws MalformedURLException, IOException {

        Bitmap bmp = null;

        BitmapFactory.Options opts = new BitmapFactory.Options();

        

        InputStream stream = new URL(url).openStream();

        byte[] bytes = getBytes(stream);

        //这3句是处理图片溢出的begin( 如果不需要处理溢出直接 opts.inSampleSize=1;)

        opts.inJustDecodeBounds = true;

        BitmapFactory.decodeByteArray(bytes, 0, bytes.length, opts);

        opts.inSampleSize = computeSampleSize(opts, -1, displaypixels);

        //end

        opts.inJustDecodeBounds = false;

        bmp = BitmapFactory.decodeByteArray(bytes, 0, bytes.length, opts);

        return bmp;

    }

    /**

     * 数据流转成btyle[]数组

     * */

    private byte[] getBytes(InputStream is) {



        ByteArrayOutputStream baos = new ByteArrayOutputStream();

        byte[] b = new byte[2048];

        int len = 0;

        try {

            while ((len = is.read(b, 0, 2048)) != -1) {

                baos.write(b, 0, len);

                baos.flush();

            }

        } catch (IOException e) {

                e.printStackTrace();

        }

        byte[] bytes = baos.toByteArray();

        return bytes;

    }

    /****

    *    处理图片bitmap size exceeds VM budget （Out Of Memory 内存溢出）

    */

    private int computeSampleSize(BitmapFactory.Options options,

            int minSideLength, int maxNumOfPixels) {

        int initialSize = computeInitialSampleSize(options, minSideLength,

                maxNumOfPixels);



        int roundedSize;

        if (initialSize <= 8) {

            roundedSize = 1;

            while (roundedSize < initialSize) {

                roundedSize <<= 1;

            }

        } else {

            roundedSize = (initialSize + 7) / 8 * 8;

        }

        return roundedSize;

    }

    

    private int computeInitialSampleSize(BitmapFactory.Options options,

            int minSideLength, int maxNumOfPixels) {

        double w = options.outWidth;

        double h = options.outHeight;

        int lowerBound = (maxNumOfPixels == -1) ? 1 : (int) Math.ceil(Math

                .sqrt(w * h / maxNumOfPixels));

        int upperBound = (minSideLength == -1) ? 128 : (int) Math.min(

                Math.floor(w / minSideLength), Math.floor(h / minSideLength));



        if (upperBound < lowerBound) {

            return lowerBound;

        }



        if ((maxNumOfPixels == -1) && (minSideLength == -1)) {

            return 1;

        } else if (minSideLength == -1) {

            return lowerBound;

        } else {

            return upperBound;

        }

    }

}

3.测试调用代码：

@Override

    public void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.main);

        ImageDownloadTask imgtask =new ImageDownloadTask();

        

        /**这里是获取手机屏幕的分辨率用来处理 图片 溢出问题的。begin*/

        DisplayMetrics dm = new DisplayMetrics();

        getWindowManager().getDefaultDisplay().getMetrics(dm);

        imgtask.setDisplayWidth(dm.widthPixels);

        imgtask.setDisplayHeight(dm.heightPixels);

        //end

        ImageView imageView_test= (ImageView)findViewById(R.id.imageView_test);

       

        imgtask.execute("http://pic.qukantu.com/big/7515/201201031116491.jpg",imageView_test);

        

    }

 

4.小结：

主要是通过   extends AsyncTask<Object, Object, Bitmap> 来实现异步的。

图片Out Of Memory 内存溢出 这一块操作，在实际应用中应该考虑淡定抽取出来。这里为了方便放进来了。 溢出处理实际上就是获得设备分辨率把图片进行压缩。