SnapKit

GitHub地址：https://github.com/SnapKit/SnapKit
中文说明：http://www.hangge.com/blog/cache/detail_1097.html

• 例子

        let redView = UIView()
        redView.backgroundColor = UIColor.red
        self.view.addSubview(redView)
        redView.snp.makeConstraints { (make) in
            make.width.height.equalTo(50)
            make.center.equalTo(self.view)
        }

• SnapKit设置百分百

   //宽度为父view的宽度的一半
    make.width.equalTo(_containerView.mas_width).multipliedBy(0.5);