android 加載大圖片時報OOM的解決方案(源碼)

 

在Android中：

　　1.一個進程的內存可以由2個部門組成：java 施用內存 ，C 施用內存 ，這兩個內存的和必需小於16M，不然就會出現各人熟悉的OOM，這個就是熬頭種OOM的情況。

　　2.一朝內存分配給Java後，以後這塊內存縱然開釋後，也只能給Java的施用，這個估計跟java虛擬機裏把內存分成好幾塊進行緩存的原因有關，反正C就別想用到這塊的內存了，所以要是Java突然佔用了一個大塊內存，縱然很快開釋了：

　　C能施用的內存 = 16M - Java某一瞬間佔在校大學生創業點子用的最大內存。

　　而Bitmap的生成是路程經過過程malloc進行內存分配的，佔用的是C的內存。

 

Code :

 

/**
 * 加載大圖片工具類：解決android加載大圖片時報OOM異常
 * 解決原理：先設置縮放選項，再讀取縮放的圖片數據到內存，規避了內存引起的OOM
 * @author: 張進 

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

    public static final int UNCONSTRAINED = -1;
    
    /*
  * 獲得設置信息
  */
 public static Options getOptions(String path){
  Options options = new Options();
  options.inJustDecodeBounds = true;//只描邊，不讀取數據
  BitmapFactory.decodeFile(path, options);
  return options;
 }
 
 
 /**
  * 獲得圖像
  * @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; //設置縮放比例
   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);
 }


 /**
  * 獲取需要進行縮放的比例，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;
        }
    }
    
 
}

 

 

工具類的使用：

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