Android 異步獲取網絡圖片並處理圖片Out Of Memory 內存溢出問題

測試環境為Adnroid 2.1以上。

1：AndroidManifest.xml 權限配置：

添加互聯網訪問權限：

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

2.異步圖片類 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;
    /***
     * 這里獲取到手機的分辨率大小
     * */
    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();
        }
    }
    /**
     * 通過URL獲得網上圖片。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);
        //這3句是處理圖片溢出的begin( 如果不需要處理溢出直接 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;
    }
    /**
     * 數據流轉成btyle[]數組
     * */
    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;
    }
    /****
    *    處理圖片bitmap size exceeds VM budget （Out Of Memory 內存溢出）
    */
    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.測試調用代碼：

@Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        ImageDownloadTask imgtask =new ImageDownloadTask();
        
        /**這里是獲取手機屏幕的分辨率用來處理 圖片 溢出問題的。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.小結：

主要是通過   extends AsyncTask<Object, Object, Bitmap> 來實現異步的。

圖片Out Of Memory 內存溢出 這一塊操作，在實際應用中應該考慮淡定抽取出來。這里為了方便放進來了。 溢出處理實際上就是獲得設備分辨率把圖片進行壓縮。