import SnapKit

class ViewController: UIViewController {
    
    private var isUpdateSnapkitV  = false
    
    private lazy var snapkitV : UIView = {
        let snapkitV = UIView()
        snapkitV.backgroundColor = UIColor.red
        return snapkitV
    }()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        self.view.addSubview(snapkitV)
        snapkitV.addGestureRecognizer(UITapGestureRecognizer.init(target: self, action: #selector(reloadView)))
        snapkitV.snp.makeConstraints { (make) in
            make.size.equalTo(CGSize(width: 100, height: 100))
            make.centerX.centerY.equalTo(view)
        }
    }
    
    
    override func updateViewConstraints() {
        
        //移除原有的重新添加
        snapkitV.snp.remakeConstraints { (make) in
            if isUpdateSnapkitV{
                make.size.equalTo(CGSize(width: UIScreen.main.bounds.size.width, height: UIScreen.main.bounds.size.width))
            }else{
                make.size.equalTo(CGSize(width: 100, height: 100))
            }
        }
        
        //更新原有的不会添加
        snapkitV.snp.updateConstraints { (make) in
            if isUpdateSnapkitV{
                make.size.equalTo(CGSize(width: UIScreen.main.bounds.size.width, height: UIScreen.main.bounds.size.width))
            }else{
                make.size.equalTo(CGSize(width: 100, height: 100))
            }
        }
        
        //最后一步在调用
        super.updateViewConstraints()
    }
}

extension ViewController{

///第一种更新动画方法 推荐 https://www.cnblogs.com/qingzZ/p/14005859.html


///第二种动画方法 不推荐
    @objc private func reloadView(){
        isUpdateSnapkitV.toggle()
        self.view.setNeedsUpdateConstraints() //标记为需要更新约束
        self.view.updateConstraintsIfNeeded()//立即调用updateViewConstraints更新约束, 此方法只是更新了约束, 并没有刷新布局
        UIView.animate(withDuration: 1.0) {
            self.view.layoutIfNeeded()//动画 刷新布局
        }
    }
}