Loading Large Bitmaps Efficiently

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在有些情况下，图片本身的大小超过了应用的需求，这时可以降低图片分辨率以降低内存消耗；

BitmapFactory提供了很多种方法用于创建bitmap（decodeByteArray(), decodeFile(),decodeResource(), etc），这些方法都可以通过设置 BitmapFactory.Options 来设定解析选项；

一，获取原图片的大小

BitmapFactory.Options options = new BitmapFactory.Options();options.inJustDecodeBounds = true;BitmapFactory.decodeResource(getResources(), R.id.myimage, options);int imageHeight = options.outHeight;int imageWidth = options.outWidth;String imageType = options.outMimeType;

二，设置图片的sample

public static int calculateInSampleSize(            BitmapFactory.Options options, int reqWidth, int reqHeight) {    // Raw height and width of image    final int height = options.outHeight;    final int width = options.outWidth;    int inSampleSize = 1;    if (height > reqHeight || width > reqWidth) {        final int halfHeight = height / 2;        final int halfWidth = width / 2;        // Calculate the largest inSampleSize value that is a power of 2 and keeps both        // height and width larger than the requested height and width.        while ((halfHeight / inSampleSize) > reqHeight                && (halfWidth / inSampleSize) > reqWidth) {            inSampleSize *= 2;        }    }    return inSampleSize;}

三，创建所需要的bitmap

public static Bitmap decodeSampledBitmapFromResource(Resources res, int resId,        int reqWidth, int reqHeight) {    // First decode with inJustDecodeBounds=true to check dimensions    final BitmapFactory.Options options = new BitmapFactory.Options();    options.inJustDecodeBounds = true;    BitmapFactory.decodeResource(res, resId, options);    // Calculate inSampleSize    options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);    // Decode bitmap with inSampleSize set    options.inJustDecodeBounds = false;    return BitmapFactory.decodeResource(res, resId, options);}

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