Android使用BitmapFactory.Options解决加载大图片内存溢出问题

Android使用BitmapFactory.Options解决加载大图片内存溢出问题

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。

1、设置缩放大小对图片作处理

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;
 }

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;
     }
 }