完美解决java.lang.OutOfMemoryError: bitmap size exceeds VM budget

转自 http://www.maxhis.info/androiding/bitmap-size-exceed/

当图片过大，或图片数量较多时使用BitmapFactory解码图片会出java.lang.OutOfMemoryError: bitmap size exceeds VM budget，要想正常使用则需分配更少的内存，具体的解决办法是修改采样值BitmapFactory.Options.inSampleSize，例 如：

 BitmapFactory.Options opts = new BitmapFactory.Options();
 opts.inSampleSize = 4;
 Bitmap bitmap = BitmapFactory.decodeFile(imageFile, opts);

如何设置恰当的inSampleSize
设置恰当的inSampleSize是解决该问题的关键之一。BitmapFactory.Options提供了另一个成员inJustDecodeBounds。

 BitmapFactory.Options opts = new BitmapFactory.Options();
 opts.inJustDecodeBounds = true;
 Bitmap bitmap = BitmapFactory.decodeFile(imageFile, opts);

设置inJustDecodeBounds为true后，decodeFile并不分配空间，但可计算出原始图片的长度和宽度，即opts.width和opts.height。有了这两个参数，再通过一定的算法，即可得到一个恰当的inSampleSize。
查看Android源码，Android提供了一种动态计算的方法。

 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 == -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 the larger one when there is no overlapping zone.
         return lowerBound;
     }

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

使用该算法，就可动态计算出图片的inSampleSize。

 BitmapFactory.Options opts = new BitmapFactory.Options();
 opts.inJustDecodeBounds = true;
 BitmapFactory.decodeFile(imageFile, opts);

 opts.inSampleSize = computeSampleSize(opts, -1, 128*128);
 opts.inJustDecodeBounds = false;
 try {
  Bitmap bmp = BitmapFactory.decodeFile(imageFile, opts);
  imageView.setImageBitmap(bmp);
     } catch (OutOfMemoryError err) {
 }

另外，可以通过

 Bitmap.recycle()

方法来释放位图所占的空间，当然前提是位图没有被使用。