网上有很多解决android加载bitmap内存溢出的方法，搜了一圈做下整理总结。项目里需求是拍摄多图之后上传，部分手机会内存溢出。
常用一种解决方法：即将载入的图片缩小，这种方式以牺牲图片的质量为代价。在BitmapFactory中有一个内部类BitmapFactory.Options，其中当options.inSampleSize值>1时，根据文档：
If set to a value > 1, requests the decoder to subsample the original image, returning a smaller image to save memory. (1 -> decodes full size; 2 -> decodes 1/4th size; 4 -> decode 1/16th size). Because you rarely need to show and have full size bitmap images on your phone. For manipulations smaller sizes are usually enough.
options.inSampleSize是以2的指数的倒数被进行放缩 现在问题是怎么确定inSampleSize的值？每张图片的放缩大小的比例应该是不一样的！这样的话就要运行时动态确定。在BitmapFactory.Options中提供了另一个成员inJustDecodeBounds。 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。Android提供了一种动态计算的方法，见computeSampleSize().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 lowerBound; } if ((maxNumOfPixels == -1) && (minSideLength == -1)) { return 1; } else if (minSideLength == -1) { return lowerBound; } else { return upperBound; }}
以上只做为参考，我们只要用这函数即可，opts.inSampleSize = computeSampleSize(opts, -1, 128*128);
要点：
1、用decodeFileDescriptor()来生成bimap比decodeFile()省内存FileInputStream is = = new FileInputStream(path);bmp = BitmapFactory.decodeFileDescriptor(is.getFD(), null, opts);
替换
Bitmap bmp = BitmapFactory.decodeFile(imageFile, opts); imageView.setImageBitmap(bmp);
原因：
查看BitmapFactory的源码，对比一下两者的实现，可以发现decodeFile()最终是以流的方式生成bitmapdecodeFile源码：
public static Bitmap decodeFile(String pathName, Options opts) { Bitmap bm = null; InputStream stream = null; try { stream = new FileInputStream(pathName); bm = decodeStream(stream, null, opts); } catch (Exception e) { /* do nothing. If the exception happened on open, bm will be null. */ } finally { if (stream != null) { try { stream.close(); } catch (IOException e) { // do nothing here } } } return bm; }
decodeFileDescriptor的源码，可以找到native本地方法decodeFileDescriptor，通过底层生成bitmap
decodeFileDescriptor源码：
public static Bitmap decodeFileDescriptor(FileDescriptor fd, Rect outPadding, Options opts) { if (nativeIsSeekable(fd)) { Bitmap bm = nativeDecodeFileDescriptor(fd, outPadding, opts); if (bm == null && opts != null && opts.inBitmap != null) { throw new IllegalArgumentException("Problem decoding into existing bitmap"); } return finishDecode(bm, outPadding, opts); } else { FileInputStream fis = new FileInputStream(fd); try { return decodeStream(fis, outPadding, opts); } finally { try { fis.close(); } catch (Throwable t) {/* ignore */} } } } private static native Bitmap nativeDecodeFileDescriptor(FileDescriptor fd,Rect padding, Options opts);
2、当在android设备中载入较大图片资源时，可以创建一些临时空间，将载入的资源载入到临时空间中。
opts.inTempStorage = new byte[16 * 1024];
完整代码：
public static OutputStream decodeBitmap(String path) { BitmapFactory.Options opts = new BitmapFactory.Options(); opts.inJustDecodeBounds = true;// 设置成了true,不占用内存，只获取bitmap宽高 BitmapFactory.decodeFile(path, opts); opts.inSampleSize = computeSampleSize(opts, -1, 1024 * 800); opts.inJustDecodeBounds = false;// 这里一定要将其设置回false，因为之前我们将其设置成了true opts.inPurgeable = true; opts.inInputShareable = true; opts.inDither = false; opts.inPurgeable = true; opts.inTempStorage = new byte[16 * 1024]; FileInputStream is = null; Bitmap bmp = null; InputStream ins = null; ByteArrayOutputStream baos = null; try { is = new FileInputStream(path); bmp = BitmapFactory.decodeFileDescriptor(is.getFD(), null, opts); double scale = getScaling(opts.outWidth * opts.outHeight, 1024 * 600); Bitmap bmp2 = Bitmap.createScaledBitmap(bmp, (int) (opts.outWidth * scale), (int) (opts.outHeight * scale), true); bmp.recycle(); baos = new ByteArrayOutputStream(); bmp2.compress(Bitmap.CompressFormat.JPEG, 100, baos); bmp2.recycle(); return baos; } catch (FileNotFoundException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } finally { try { is.close(); ins.close(); baos.close(); } catch (IOException e) { e.printStackTrace(); } System.gc(); } return baos; }private static double getScaling(int src, int des) {/** * 目标尺寸÷原尺寸 sqrt开方，得出宽高百分比 */ double scale = Math.sqrt((double) des / (double) src); return scale;}