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bitmap
decodeFile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;
}
