Android（decode文件转成bitmap）使用BitmapFactory.Options解决加载大图片内存溢出

来自于  http://orgcent.com/android-outofmemoryerror-load-big-image/

由于Android对图片使用内存有限制，若是加载几兆的大图片便内存溢出。Bitmap会将图片的所有像素（即长x宽）加载到内存中，如果图片分辨率过大，会直接导致内存溢出（java.lang.OutOfMemoryError），只有在BitmapFactory加载图片时使用BitmapFactory.Options对相关参数进行配置来减少加载的像素。

public Bitmap getBitmapFromFile(File dst, int width, int height) {    if (null != dst && dst.exists()) {        BitmapFactory.Options opts = null;        if (width > 0 && height > 0) {            opts = new BitmapFactory.Options();            opts.inJustDecodeBounds = true;            BitmapFactory.decodeFile(dst.getPath(), opts);            // 计算图片缩放比例            final int minSideLength = Math.min(width, height);            opts.inSampleSize = computeSampleSize(opts, minSideLength,                    width * height);            opts.inJustDecodeBounds = false;            opts.inInputShareable = true;            opts.inPurgeable = true;        }        try {            return BitmapFactory.decodeFile(dst.getPath(), opts);        } catch (OutOfMemoryError e) {            e.printStackTrace();        }    }    return null;}

计算比例：

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;    }}