快速放置在函数中时无法触发uiview.animate

Question

我无法触发动画，我将下面的函数放在viewdidload 函数之外，并创建了一个自定义函数，该函数将在点击按钮时触发。但是它没有创建动画，而是在下面给了我一个错误。这是错误

Thread 1: Fatal error: Unexpectedly found nil while unwrapping an Optional value

这是要触发的函数

@objc func triggeranimation(){
        UIView.animate(withDuration: 0.5, animations: {
            let intro:introViewController = introViewController()
            intro.Title.backgroundColor = UIColor.blue
        }, completion: nil)
    }

我在 viewdidload 中以编程方式添加了按钮，该按钮将触发上述功能。我尝试将自定义函数放在 viewdidload 函数之前和之后，但错误结果相同。请帮助为什么它告诉我当我清楚地在同一个视图控制器中时它发现为零。

let nextBtn = UIButton(frame: CGRect(x:0, y: 0, width: 0, height: 0))
        nextBtn.translatesAutoresizingMaskIntoConstraints = false
        nextBtn.setTitle("Next", for: UIControlState.normal)
        nextBtn.backgroundColor = UIColor.blue
        nextBtn.addTarget(self, action: Selector("triggeranimation"), for: .touchUpInside)
        nextBtn.setTitleColor(UIColor.white, for: .normal)
        self.view.addSubview(nextBtn)
        // width cant change for some unknown reason
        nextBtn.widthAnchor.constraint(equalToConstant: 10)
        nextBtn.heightAnchor.constraint(equalToConstant: 20)
        nextBtn.bottomAnchor.constraint(equalTo: view.bottomAnchor, constant: -20).isActive = true
        nextBtn.rightAnchor.constraint(equalTo: view.rightAnchor, constant: -10).isActive = true

完整代码

class introViewController: UIViewController{
    var Title:UILabel!
    var nextBtn:UIButton!

override func viewDidLoad() {
        super.viewDidLoad()
 let Title = UILabel(frame: CGRect(x: self.view.frame.size.width / 2, y: (self.view.frame.size.height + 30), width: 50, height: 10))
        Title.translatesAutoresizingMaskIntoConstraints = false
        Title.text = "WELCOME"
        Title.font = UIFont.systemFont(ofSize: 24, weight: .bold)
        Title.textAlignment = .center
        Title.textColor = UIColor.black
        self.view.addSubview(Title)
        Title.bottomAnchor.constraint(equalTo: view.bottomAnchor, constant: -250).isActive = true
        Title.centerXAnchor.constraint(equalTo: view.centerXAnchor, constant: 0).isActive = true

let nextBtn = UIButton(frame: CGRect(x:0, y: 0, width: 0, height: 0))
        nextBtn.translatesAutoresizingMaskIntoConstraints = false
        nextBtn.setTitle("Next", for: UIControlState.normal)
        nextBtn.backgroundColor = UIColor.blue
        nextBtn.addTarget(self, action: Selector("triggeranimation"), for: .touchUpInside)
        nextBtn.setTitleColor(UIColor.white, for: .normal)
        self.view.addSubview(nextBtn)
        // width cant change for some unknown reason
        nextBtn.widthAnchor.constraint(equalToConstant: 10)
        nextBtn.heightAnchor.constraint(equalToConstant: 20)
        nextBtn.bottomAnchor.constraint(equalTo: view.bottomAnchor, constant: -20).isActive = true
        nextBtn.rightAnchor.constraint(equalTo: view.rightAnchor, constant: -10).isActive = true


}

@objc func triggeranimation(){
        UIView.animate(withDuration: 0.5, animations: {
            let intro:introViewController = introViewController()
            intro.Title.backgroundColor = UIColor.blue
        }, completion: nil)
    }
}

此外，我还尝试将 UIView.animate 移动到 viewdidload 中，但它根本没有动画，它只是立即改变颜色。

更新：我确实通过更改 Title 变量解决了发现的 nil 问题 var Title:UILabel! 转为var Title:UILabel! = UILabel()

但我仍然对动画有问题，即使我将 DURATION 延长到 5.0，它也没有使任何动画立即改变颜色

Answer 1

问题在于intro 是一个新初始化的视图控制器，它与所讨论的实例完全无关。例如，不会在该新实例上调用 viewDidLoad。相反，您只想使用“self”，即加载的视图控制器。

@objc func triggeranimation(){
    UIView.animate(withDuration: 0.5, animations: {
        //let intro:introViewController = introViewController()
        self.Title.backgroundColor = UIColor.blue
    }, completion: nil)
}

您的 viewDidLoad 代码中似乎也存在问题，您正在尝试初始化 Title 和 nextBtn 属性。相反，您不小心创建了同名的本地常量。这就是为什么您的属性为零的原因。

 // You have this now, which creates a local constant
 //let Title = UILabel(.. 

 // You want this instead, which initializes your property
 self.Title = UILabel(.. 

当然，对 nextBtn 做同样的事情。