Question

获取以下错误消息

＆＃34;致命错误：在展开可选值时意外发现nil＆＃34;

就这一部分而言所有图像都没问题。

(segue.destination as! DetailViewController).imgView.image = UIImage(named: "horsestar.png")!

下面的代码是整个准备功能

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    // Get the new view controller using segue.destinationViewController.
    // Pass the selected object to the new view controller.
    if segue.identifier == "dog" {
        let imgView = UIImageView(image: UIImage(named: "dogstar.png")!)
        print("dog")

        (segue.destination as! DetailViewController).scrollView.addSubview(imgView)
    } else if segue.identifier == "horse" {
        print("horse")
        (segue.destination as! DetailViewController).imgView.image = UIImage(named: "horsestar.png")!
        (segue.destination as! DetailViewController).scrollView.addSubview((segue.destination as! DetailViewController).imgView)
    } else if segue.identifier == "bear" {
        let imageView = UIImageView(image: UIImage(named: "bear.png")!)
        print("bear")
    } else if segue.identifier == "eagle" {
        let imageView = UIImageView(image: UIImage(named: "eagle.png")!)
        print("eagle")
    } else {
        let imageView = UIImageView(image: UIImage(named: "rabbit.png")!)
        print("rabbit")
    }
}

Answer 1

小心强制解包（！），因为它在运行时传播了很多错误。如果您的代码中不希望nil值，则为用户guard let。

在您的代码中：

(segue.destination as! DetailViewController).imgView.image = UIImage(named: "horsestar.png")!

你有两个危险的地方：

将segue.destination投放到DetailViewController。如果不可能，请抛出"fatal error: unexpectedly found nil while unwrapping an Optional value"
加载名称为“horsestar.png”的图片。如果图像未成立，请抛出"fatal error: unexpectedly found nil while unwrapping an Optional value"

更好地使用guard let（或if let）：

guard let destinationViewController = segue.destination as? DetailViewController else {
    print("unable to get destinationViewController")
    return
}

guard let image = UIImage(named: "horsestar.png") else {
    print("unable to load image")
    return
}

destinationViewController.imgView.image = image

Answer 2

在else if条件下更改您的代码

else if segue.identifier == "horse" {
    if let toViewController = segue.destination as? DetailViewController {
      toViewController.imgView.image = UIImage(named: "horsestar.png")

     /// your other stuff 
    }
}

还不知道下面的代码你想要什么？

  (segue.destination as! DetailViewController).scrollView.addSubview((segue.destination as! DetailViewController).imgView)

我可以使用segue prepare函数处理detailViewController中的滚动视图

2 个答案: