Bitmap高效加载

 options.inJustDecodeBounds = true;

int InSampleSize = 1;

 int Height = options.outHeight;
 int Width = options.outWidth;

 private Bitmap LoadBitmapFromResource(Resources resources,int Res,int HopeHeight,int HopeWidth){
        final BitmapFactory.Options options = new BitmapFactory.Options();
        //用于解析图片的宽/高，并不会加载图片
        options.inJustDecodeBounds = true;
        //从resources里面加载图片
        BitmapFactory.decodeResource( resources,Res,options );
        //计算采样率
        options.inSampleSize = CalculateInSampleSize( options,HopeHeight,HopeWidth );
        options.inJustDecodeBounds = false;
        return BitmapFactory.decodeResource( resources,Res,options );
    }
    public static int CalculateInSampleSize(BitmapFactory.Options options,int HopeHeight,int HopeWidth){
    //获取原始图片的宽/高
        int Height = options.outHeight;
        int Width = options.outWidth;
        //采样率为1，即图片大小为原始尺寸
        int InSampleSize = 1;
        //如果获取图片的原始高度大小你所期望的图片大小才有缩放的意义。
        //如果大于的话，第一次获取它们的一般，然后除了采样率如果还大于期望的宽/高
        //表示还可以继续缩小。采样率累乘2，InSampleSize的取值为1,2,4,8,16,32...其值为2的指数。
        if (Height > HopeHeight && Width > HopeWidth){
            int HalfHeight = Height / 2;
            int HalfWidth = Width / 2;
            while ((HalfHeight / InSampleSize ) >= HopeHeight && (HalfWidth / InSampleSize) >= HopeWidth){
                InSampleSize *= 2;
            }
        }
        return InSampleSize;
    }

 UseBitmapFactory.setImageBitmap( LoadBitmapFromResource( getResources(), R.drawable.background,200,200) );