给UIView添加底线方法

好看的底线颜色： [UIColor colorWithRed:70.0/255.0 green:70.0/255.0 blue:70.0/255.0 alpha:1.0]

_addBottomMenuHairline 用于判断是否添加底边
           

if (_addBottomMenuHairline) {
        UIView *menuBottomHairline = [UIView new];
        
        menuBottomHairline.translatesAutoresizingMaskIntoConstraints = NO;
        
        [self.view addSubview:menuBottomHairline];
        
        NSArray *menuBottomHairline_constraint_H = [NSLayoutConstraint constraintsWithVisualFormat:@"H:|[menuBottomHairline]|" options:0 metrics:nil views:@{@"menuBottomHairline":menuBottomHairline}];
        NSString *menuBottomHairline_constraint_V_Format = [NSString stringWithFormat:@"V:|-%f-[menuBottomHairline(0.5)]",_menuHeight];
        NSArray *menuBottomHairline_constraint_V = [NSLayoutConstraint constraintsWithVisualFormat:menuBottomHairline_constraint_V_Format options:0 metrics:nil views:@{@"menuBottomHairline":menuBottomHairline}];
        
        [self.view addConstraints:menuBottomHairline_constraint_H];
        [self.view addConstraints:menuBottomHairline_constraint_V];
        
        menuBottomHairline.backgroundColor = _bottomMenuHairlineColor;
    }