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。

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