iOS 圓角投影

    self.backgroundColor = [UIColor whiteColor];
    self.layer.shadowColor = [UIColor lightGrayColor].CGColor;
    self.layer.shadowOffset = CGSizeMake(0,0);
    self.layer.shadowOpacity = 0.5;
    self.layer.cornerRadius = 12;
    self.layer.masksToBounds = YES;
    self.clipsToBounds = NO;