android BitmapFactory的OutOfMemoryError: bitmap ...

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bitmapdecodeFileDescriptor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trueopts.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;}