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().
[size=1em]1 [size=1em]2 [size=1em]3 [size=1em]4 [size=1em]5 [size=1em]6 [size=1em]7 [size=1em]8 [size=1em]9 [size=1em]10 [size=1em]11 [size=1em]12 [size=1em]13 [size=1em]14 [size=1em]15 [size=1em]16 [size=1em]17 [size=1em]18 [size=1em]19 [size=1em]20 [size=1em]21 [size=1em]22 [size=1em]23 [size=1em]24 [size=1em]25 [size=1em]26 [size=1em]27 [size=1em]28 [size=1em]29 [size=1em]30 [size=1em]31 [size=1em]32 [size=1em]33 [size=1em]34 [size=1em]35 [size=1em]36 [size=1em]37 [size=1em]38 [size=1em]39 [size=1em]40 [size=1em]41 [size=1em]42 | [size=1em][size=1em]public static int computeSampleSize(BitmapFactory.Options options, [size=1em] int minSideLength, int maxNumOfPixels) { [size=1em] int initialSize = computeInitialSampleSize(options, minSideLength, [size=1em] maxNumOfPixels); [size=1em] [size=1em] int roundedSize; [size=1em] if (initialSize <= 8) { [size=1em] roundedSize = 1; [size=1em] while (roundedSize < initialSize) { [size=1em] roundedSize <<= 1; [size=1em] } [size=1em] } else { [size=1em] roundedSize = (initialSize + 7) / 8 * 8; [size=1em] } [size=1em] [size=1em] return roundedSize; [size=1em]} [size=1em] [size=1em]private static int computeInitialSampleSize(BitmapFactory.Options options, [size=1em] int minSideLength, int maxNumOfPixels) { [size=1em] double w = options.outWidth; [size=1em] double h = options.outHeight; [size=1em] [size=1em] int lowerBound = (maxNumOfPixels == -1) ? 1 : [size=1em] (int) Math.ceil(Math.sqrt(w * h / maxNumOfPixels)); [size=1em] int upperBound = (minSideLength == -1) ? 128 : [size=1em] (int) Math.min(Math.floor(w / minSideLength), [size=1em] Math.floor(h / minSideLength)); [size=1em] [size=1em] if (upperBound < lowerBound) { [size=1em] return lowerBound; [size=1em] } [size=1em] [size=1em] if ((maxNumOfPixels == -1) && [size=1em] (minSideLength == -1)) { [size=1em] return 1; [size=1em] } else if (minSideLength == -1) { [size=1em] return lowerBound; [size=1em] } else { [size=1em] return upperBound; [size=1em] } [size=1em]} |
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
[size=1em]1 [size=1em]2 | [size=1em][size=1em]FileInputStream is = = new FileInputStream(path); [size=1em]bmp = BitmapFactory.decodeFileDescriptor(is.getFD(), null, opts); |
替换
[size=1em]1 [size=1em]2 | [size=1em][size=1em]Bitmap bmp = BitmapFactory.decodeFile(imageFile, opts); [size=1em] 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bitmap
decodeFile源码：
[size=1em]1 [size=1em]2 [size=1em]3 [size=1em]4 [size=1em]5 [size=1em]6 [size=1em]7 [size=1em]8 [size=1em]9 [size=1em]10 [size=1em]11 [size=1em]12 [size=1em]13 [size=1em]14 [size=1em]15 [size=1em]16 [size=1em]17 [size=1em]18 [size=1em]19 [size=1em]20 [size=1em]21 | [size=1em][size=1em]public static Bitmap decodeFile(String pathName, Options opts) { [size=1em] Bitmap bm = null; [size=1em] InputStream stream = null; [size=1em] try { [size=1em] stream = new FileInputStream(pathName); [size=1em] bm = decodeStream(stream, null, opts); [size=1em] } catch (Exception e) { [size=1em] /* do nothing. [size=1em] If the exception happened on open, bm will be null. [size=1em] */ [size=1em] } finally { [size=1em] if (stream != null) { [size=1em] try { [size=1em] stream.close(); [size=1em] } catch (IOException e) { [size=1em] // do nothing here [size=1em] } [size=1em] } [size=1em] } [size=1em] return bm; [size=1em]} |
decodeFileDescriptor的源码，可以找到native本地方法decodeFileDescriptor，通过底层生成bitmap
decodeFileDescriptor源码：
[size=1em]1 [size=1em]2 [size=1em]3 [size=1em]4 [size=1em]5 [size=1em]6 [size=1em]7 [size=1em]8 [size=1em]9 [size=1em]10 [size=1em]11 [size=1em]12 [size=1em]13 [size=1em]14 [size=1em]15 [size=1em]16 [size=1em]17 [size=1em]18 [size=1em]19 [size=1em]20 | [size=1em][size=1em] public static Bitmap decodeFileDescriptor(FileDescriptor fd, Rect outPadding, Options opts) { [size=1em] if (nativeIsSeekable(fd)) { [size=1em] Bitmap bm = nativeDecodeFileDescriptor(fd, outPadding, opts); [size=1em] if (bm == null && opts != null && opts.inBitmap != null) { [size=1em] throw new IllegalArgumentException("Problem decoding into existing bitmap"); [size=1em] } [size=1em] return finishDecode(bm, outPadding, opts); [size=1em] } else { [size=1em] FileInputStream fis = new FileInputStream(fd); [size=1em] try { [size=1em] return decodeStream(fis, outPadding, opts); [size=1em] } finally { [size=1em] try { [size=1em] fis.close(); [size=1em] } catch (Throwable t) {/* ignore */} [size=1em] } [size=1em] } [size=1em] } [size=1em]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。
[size=1em]1 | [size=1em][size=1em]opts.inTempStorage = new byte[16 * 1024]; |
完整代码：
[size=1em]1 [size=1em]2 [size=1em]3 [size=1em]4 [size=1em]5 [size=1em]6 [size=1em]7 [size=1em]8 [size=1em]9 [size=1em]10 [size=1em]11 [size=1em]12 [size=1em]13 [size=1em]14 [size=1em]15 [size=1em]16 [size=1em]17 [size=1em]18 [size=1em]19 [size=1em]20 [size=1em]21 [size=1em]22 [size=1em]23 [size=1em]24 [size=1em]25 [size=1em]26 [size=1em]27 [size=1em]28 [size=1em]29 [size=1em]30 [size=1em]31 [size=1em]32 [size=1em]33 [size=1em]34 [size=1em]35 [size=1em]36 [size=1em]37 [size=1em]38 [size=1em]39 [size=1em]40 [size=1em]41 [size=1em]42 [size=1em]43 [size=1em]44 [size=1em]45 [size=1em]46 [size=1em]47 [size=1em]48 [size=1em]49 [size=1em]50 [size=1em]51 [size=1em]52 | [size=1em][size=1em]public static OutputStream decodeBitmap(String path) { [size=1em] BitmapFactory.Options opts = new BitmapFactory.Options(); [size=1em] opts.inJustDecodeBounds = true;// 设置成了true,不占用内存，只获取bitmap宽高 [size=1em] BitmapFactory.decodeFile(path, opts); [size=1em] opts.inSampleSize = computeSampleSize(opts, -1, 1024 * 800); [size=1em] 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 [size=1em] opts.inPurgeable = true; [size=1em] opts.inInputShareable = true; [size=1em] opts.inDither = false; [size=1em] opts.inPurgeable = true; [size=1em] opts.inTempStorage = new byte[16 * 1024]; [size=1em] FileInputStream is = null; [size=1em] Bitmap bmp = null; [size=1em] InputStream ins = null; [size=1em] ByteArrayOutputStream baos = null; [size=1em] try { [size=1em] is = new FileInputStream(path); [size=1em] bmp = BitmapFactory.decodeFileDescriptor(is.getFD(), null, opts); double scale = getScaling(opts.outWidth * opts.outHeight, 1024 * 600); [size=1em] Bitmap bmp2 = Bitmap.createScaledBitmap(bmp, [size=1em] (int) (opts.outWidth * scale), [size=1em] (int) (opts.outHeight * scale), true); [size=1em] bmp.recycle(); [size=1em] baos = new ByteArrayOutputStream(); [size=1em] bmp2.compress(Bitmap.CompressFormat.JPEG, 100, baos); [size=1em] bmp2.recycle(); [size=1em] return baos; [size=1em] } catch (FileNotFoundException e) { [size=1em] e.printStackTrace(); [size=1em] } catch (IOException e) { [size=1em] e.printStackTrace(); [size=1em] } finally { [size=1em] try { [size=1em] is.close(); [size=1em] ins.close(); [size=1em] baos.close(); [size=1em] } catch (IOException e) { [size=1em] e.printStackTrace(); [size=1em] } [size=1em] System.gc(); [size=1em] } [size=1em] return baos; [size=1em] } [size=1em]private static double getScaling(int src, int des) { [size=1em]/** [size=1em] * 目标尺寸÷原尺寸 sqrt开方，得出宽高百分比 [size=1em] */ [size=1em] double scale = Math.sqrt((double) des / (double) src); [size=1em] return scale; [size=1em]} |
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