//通常用于刪除緩存的時，計算緩存大小//單個文件的大小- (long long) fileSizeAtPath:(NSString*) filePath{    NSFileManager* manager = [NSFileManager defaultManager];    if ([manager fileExistsAtPath:filePath]){        return [[manager attributesOfItemAtPath:filePath error:nil] fileSize];    }    return 0;}//遍歷文件夾獲得文件夾大小，返回多少M- (float ) folderSizeAtPath:(NSString*) folderPath{    NSFileManager* manager = [NSFileManager defaultManager];    if (![manager fileExistsAtPath:folderPath]) return 0;    NSEnumerator *childFilesEnumerator = [[manager subpathsAtPath:folderPath] objectEnumerator];    NSString* fileName;    long long folderSize = 0;    while ((fileName = [childFilesEnumerator nextObject]) != nil){        NSString* fileAbsolutePath = [folderPath stringByAppendingPathComponent:fileName];        folderSize += [self fileSizeAtPath:fileAbsolutePath];    }    return folderSize/(1024.0*1024.0);}