Swift NSLayoutConstraint 添加约束

  lazy var cancelBtn: UIButton = {
    let button = UIButton()
    button.translatesAutoresizingMaskIntoConstraints = false //这句一定要写
    button.setTitle(NSLocalizedString("cancel", comment: ""), for: .normal)
    button.setTitleColor(UIColor.ne_blueText, for: .normal)
    button.titleLabel?.font = UIFont.systemFont(ofSize: 13)
    button.addTarget(self, action: #selector(cancelBtnClick), for: .touchUpInside)

    return button
  }()

addSubview(cancelBtn)

  NSLayoutConstraint.activate([
      cancelBtn.leftAnchor.constraint(equalTo: leftAnchor, constant: 15),
      cancelBtn.topAnchor.constraint(equalTo: topAnchor, constant: 8),
      cancelBtn.widthAnchor.constraint(equalToConstant: 45),
    ])

    if #available(iOS 11.0, *) {
      NSLayoutConstraint.activate([
        copyright.centerXAnchor.constraint(equalTo: view.centerXAnchor),
        copyright.bottomAnchor.constraint(
          equalTo: view.safeAreaLayoutGuide.bottomAnchor,
          constant: -48
        ),
      ])
    }

func setupSubviews() {
    view.addSubview(textfieldBgView)
    if #available(iOS 11.0, *) {
      NSLayoutConstraint.activate([
        textfieldBgView.leftAnchor.constraint(equalTo: view.leftAnchor, constant: 20.0),
        textfieldBgView.rightAnchor.constraint(equalTo: view.rightAnchor, constant: -20),
        textfieldBgView.topAnchor.constraint(
          equalTo: view.safeAreaLayoutGuide.topAnchor,
          constant: 12
        ),
        textfieldBgView.heightAnchor.constraint(equalToConstant: 50),
      ])
    } else {
      if #available(iOS 10.0, *) {
        NSLayoutConstraint.activate([
          textfieldBgView.leftAnchor.constraint(equalTo: view.leftAnchor, constant: 20.0),
          textfieldBgView.rightAnchor.constraint(equalTo: view.rightAnchor, constant: -20),
          textfieldBgView.topAnchor.constraint(equalTo: view.topAnchor, constant: 12),
          textfieldBgView.heightAnchor.constraint(equalToConstant: 50),
        ])
      } else {
        NSLayoutConstraint.activate([
          textfieldBgView.leftAnchor.constraint(equalTo: view.leftAnchor, constant: 20.0),
          textfieldBgView.rightAnchor.constraint(equalTo: view.rightAnchor, constant: -20),
          textfieldBgView.topAnchor.constraint(equalTo: view.topAnchor, constant: 12 + kNavigationHeight + KStatusBarHeight),
          textfieldBgView.heightAnchor.constraint(equalToConstant: 50),
        ])
      }
    }

    textfieldBgView.addSubview(textField)
    NSLayoutConstraint.activate([
      textField.leftAnchor.constraint(equalTo: textfieldBgView.leftAnchor, constant: 16),
      textField.rightAnchor.constraint(equalTo: textfieldBgView.rightAnchor, constant: -12),
      textField.topAnchor.constraint(equalTo: textfieldBgView.topAnchor, constant: 0),
      textField.heightAnchor.constraint(equalToConstant: 44),
    ])
  }