public static Bitmap decodeSampledBitmapFromResource( Resources res,int resId,int reqWidth,int reqHeight){
//先通過inJustDecodeBounds=true獲取圖片尺寸
BitmapFactory.Option options=new BitmapFactory.Options();
options.inJustDecodeBounds=true;
BitmapFactory.decodeResource(res,resId,options);
//根據圖片分辨率以及實際需要的展示尺寸,計算壓縮率
options.inSampleSize=calculateInSampleSize(options,reqWidth,reqHeight);
//設置壓縮率,並解碼
options.inJustDecodeBounds=false;
return BitmapFactory.decodeResource(res,resId,options);
}