android 加载大图片时报OOM的解决方案(源码)

在Android中：

　　1.一个进程的内存可以由2个部门组成：java 施用内存 ，C 施用内存 ，这两个内存的和必需小于16M，不然就会出现各人熟悉的OOM，这个就是熬头种OOM的情况。

　　2.一朝内存分配给Java后，以后这块内存纵然开释后，也只能给Java的施用，这个估计跟java虚拟机里把内存分成好几块进行缓存的原因有关，反正C就别想用到这块的内存了，所以要是Java突然占用了一个大块内存，纵然很快开释了：

　　C能施用的内存 = 16M - Java某一瞬间占在校大学生创业点子用的最大内存。

　　而Bitmap的生成是路程经过过程malloc进行内存分配的，占用的是C的内存。

Code :

/**
 * 加载大图片工具类：解决android加载大图片时报OOM异常
 * 解决原理：先设置缩放选项，再读取缩放的图片数据到内存，规避了内存引起的OOM
 * @author: 张进 

 * @time:2011/7/28
 */
public class BitmapUtil {

    public static final int UNCONSTRAINED = -1;
    
    /*
  * 获得设置信息
  */
 public static Options getOptions(String path){
  Options options = new Options();
  options.inJustDecodeBounds = true;//只描边，不读取数据
  BitmapFactory.decodeFile(path, options);
  return options;
 }
 
 
 /**
  * 获得图像
  * @param path
  * @param options
  * @return
  * @throws FileNotFoundException
  */
 public static Bitmap getBitmapByPath(String path, Options options , int screenWidth , int screenHeight)throws FileNotFoundException{
  File file = new File(path);
  if(!file.exists()){
   throw new FileNotFoundException();
  }
  FileInputStream in = null;
  in = new FileInputStream(file);
  if(options != null){
   Rect r = getScreenRegion(screenWidth,screenHeight);
   int w = r.width();
   int h = r.height();
   int maxSize = w > h ? w : h;
   int inSimpleSize = computeSampleSize(options, maxSize, w * h);
   options.inSampleSize = inSimpleSize; //设置缩放比例
   options.inJustDecodeBounds = false;
  }
  Bitmap b = BitmapFactory.decodeStream(in, null, options);
  try {
   in.close();
  } catch (IOException e) {
   e.printStackTrace();
  }
  return b;
 }
 
 
    
 private static Rect getScreenRegion(int width , int height) {
  return new Rect(0,0,width,height);
 }


 /**
  * 获取需要进行缩放的比例，即options.inSampleSize
  * @param options
  * @param minSideLength
  * @param maxNumOfPixels
  * @return
  */
 public static 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 static int computeInitialSampleSize(BitmapFactory.Options options,
            int minSideLength, int maxNumOfPixels) {
        double w = options.outWidth;
        double h = options.outHeight;

        int lowerBound = (maxNumOfPixels == UNCONSTRAINED) ? 1 :
                (int) Math.ceil(Math.sqrt(w * h / maxNumOfPixels));
        int upperBound = (minSideLength == UNCONSTRAINED) ? 128 :
                (int) Math.min(Math.floor(w / minSideLength),
                Math.floor(h / minSideLength));

        if (upperBound < lowerBound) {
            // return the larger one when there is no overlapping zone.
            return lowerBound;
        }

        if ((maxNumOfPixels == UNCONSTRAINED) &&
                (minSideLength == UNCONSTRAINED)) {
            return 1;
        } else if (minSideLength == UNCONSTRAINED) {
            return lowerBound;
        } else {
            return upperBound;
        }
    }
    
 
}

工具类的使用：

 String path = "/sdcard/test2.jpg";
     try {
   Bitmap bitmap = BitmapUtil.getBitmapByPath(path, BitmapUtil.getOptions(path), screenWidth, screenHeight);
  } catch (FileNotFoundException e) {
   e.printStackTrace();
  }