java.lang.OutOfMemoryError: bitmap size exceeds VM budget解决方法

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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);

如何设置恰当的inSampleSize

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) {
    }

另外,可以通过Bitmap.recycle()方法来释放位图所占的空间,当然前提是位图没有被使用。

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