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

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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