BitmapFactory。Options.inSampleSize用法

来源：互联网发布：美工刀片厚度编辑：程序博客网时间：2024/05/16 03:29

BitmapFactory.decodeFile(imageFile);

用BitmapFactory解码一张图片时，有时会遇到该错误。这往往是由于图片过大造成的。要想正常使用，则需要分配更少的内存空间来存储。

BitmapFactory.Options.inSampleSize

设置恰当的inSampleSize可以使BitmapFactory分配更少的空间以消除该错误。inSampleSize的具体含义请参考SDK文档。例如：

BitmapFactory.Options opts = new BitmapFactory.Options();opts.inSampleSize = 4;Bitmap bitmap = BitmapFactory.decodeFile(imageFile, opts);

设置恰当的inSampleSize是解决该问题的关键之一。BitmapFactory.Options提供了另一个成员inJustDecodeBounds。

BitmapFactory.Options opts = new BitmapFactory.Options();opts.inJustDecodeBounds = true;Bitmap bitmap = BitmapFactory.decodeFile(imageFile, opts);

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。

查看Android源码，Android提供了一种动态计算的方法。

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;    }} 使用该算法，就可动态计算出图片的inSampleSize。BitmapFactory.Options opts = new BitmapFactory.Options();opts.inJustDecodeBounds = true;BitmapFactory.decodeFile(imageFile, opts);   opts.inSampleSize = computeSampleSize(opts, -1, 128*128);  opts.inJustDecodeBounds = false;try { Bitmap bmp = BitmapFactory.decodeFile(imageFile, opts); imageView.setImageBitmap(bmp);    } catch (OutOfMemoryError err) {    }