Question

当用户接触到imageview时，我尝试使用if语句来更改约束。现在，我的代码从小到大变化，但从大到小都没有变化。因此，if语句只能工作一次，而不能再次工作。

 var counter = 0

    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)

        let tap = UITapGestureRecognizer(target: self, action: #selector(ViewController.handleRegisterC))
        FIRE.addGestureRecognizer(tap)
        FIRE.isUserInteractionEnabled = true
        print(counter)

    }
override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view, typically from a nib.

        view.addSubview(FIRE)
    FIRE.centerXAnchor.constraint(equalTo: view.centerXAnchor).isActive = true
    FIRE.topAnchor.constraint(equalTo: view.topAnchor, constant: 0).isActive = true



    FIRE.widthAnchor.constraint(equalToConstant: 400).isActive = true
    FIRE.heightAnchor.constraint(equalToConstant: 700).isActive = true
     FIRE.translatesAutoresizingMaskIntoConstraints = false



    @objc func handleRegisterC(sender: UIButton){

        counter += 1


        if counter % 2 == 0 {


            FIRE.centerXAnchor.constraint(equalTo: view.centerXAnchor).isActive = true
            FIRE.topAnchor.constraint(equalTo: view.topAnchor, constant: 0).isActive = true


            FIRE.widthAnchor.constraint(equalToConstant: 400).isActive = true
            FIRE.heightAnchor.constraint(equalToConstant: 700).isActive = true
            FIRE.translatesAutoresizingMaskIntoConstraints = false

        }
        if counter % 2 == 1 {
            FIRE.topAnchor.constraint(equalTo: view.topAnchor, constant: 0).isActive = true
            FIRE.bottomAnchor.constraint(equalTo: view.bottomAnchor, constant: 0).isActive = true
            FIRE.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 0).isActive = true
            FIRE.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: 0).isActive = true
            FIRE.translatesAutoresizingMaskIntoConstraints = false


        }


    }



}

Answer 1

我不认为if statement只工作一次（您可以在每个块中添加打印语句以进行确认）。我认为问题在于您有两组同时处于活动状态的约束。您可能想要做的是在这两组之间交替进行；将其中一个设为活动状态，将另一个设为非活动状态。试试这样的东西

enum Size {
    case big
    case small
}
var counter = 0

override func viewDidLoad() {
    super.viewDidLoad()
    view.addSubview(FIRE)
    changeSizeTo(.small)
}

override func viewDidAppear(_ animated: Bool) {
    super.viewDidAppear(animated)
    let tap = UITapGestureRecognizer(target: self, action: #selector(ViewController.handleRegisterC))
    FIRE.addGestureRecognizer(tap)
    FIRE.isUserInteractionEnabled = true
}

private func changeSizeTo(_ size: Size) {
    FIRE.centerXAnchor.constraint(equalTo: view.centerXAnchor).isActive = size == .small
    FIRE.topAnchor.constraint(equalTo: view.topAnchor, constant: 0).isActive = size == .small
    FIRE.widthAnchor.constraint(equalToConstant: 400).isActive = size == .small
    FIRE.heightAnchor.constraint(equalToConstant: 700).isActive = size == .small
    FIRE.topAnchor.constraint(equalTo: view.topAnchor, constant: 0).isActive = size == .big
    FIRE.bottomAnchor.constraint(equalTo: view.bottomAnchor, constant: 0).isActive = size == .big
    FIRE.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 0).isActive = size == .big
    FIRE.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: 0).isActive = size == .big
    FIRE.translatesAutoresizingMaskIntoConstraints = false
}

@objc func handleRegisterC(sender: UIButton){
    counter += 1
    changeSizeTo(counter % 2 == 0 ? .small : .big)
}

swift4中的if语句不会触发addGestureRecognizer

1 个答案: