Question

我有tableView，其中有imageView和label，当我选择单元格时，我想推送另一个viewController并在其中显示我选择的单元格imageView.image和label.text，但是有错误（意外地发现nil在图像行中隐式展开一个Optional值）

func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
    let vc = storyboard?.instantiateViewController(withIdentifier: "PushedViewController") as? PushedViewController
    vc?.pushedImage.image = UIImage(named: imagesArray[indexPath.row])
    vc?.pushedLabel.text = imagesArray[indexPath.row]
    self.navigationController?.pushViewController(vc!, animated: true)
}

意外发现nil，同时隐式展开一个可选值

Answer 1

您发布的内容不多，但崩溃的行似乎是

self.navigationController?.pushViewController(vc!, animated: true)

您确定此storyboard?.instantiateViewController(withIdentifier: "PushedViewController") as? PushedViewController不是nil吗？

也许PushedViewController不在同一个情节提要中。无论如何，只要将其放在guard let中即可展开可选

func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
    guard let vc = storyboard?.instantiateViewController(withIdentifier: "PushedViewController") as? PushedViewController else { //fallback goes here return }
    vc.pushedImage.image = UIImage(named: imagesArray[indexPath.row])
    vc.pushedLabel.text = imagesArray[indexPath.row]
    self.navigationController?.pushViewController(vc, animated: true)
}

Answer 2

在您的第一个视图控制器中，selectedImage和selectedText在tableView didSelectRowAt方法中将为零。 IBOutlet仅在您按下第二个视图控制器后才会启动。因此，在第二个视图控制器中创建一个UIImage和String变量，并将值发送到这些变量。在第二个视图控制器的viewDidLoad方法中，将传递的值分配给IBOutlet。

func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
    let vc = storyboard?.instantiateViewController(withIdentifier: "PushedViewController") as? PushedViewController
    //vc?.pushedImage vc?.pushedLabel are nil
    vc?.selectedImage = UIImage(named: imagesArray[indexPath.row])
    vc?.selectedText = imagesArray[indexPath.row]
    self.navigationController?.pushViewController(vc!, animated: true)
}

PushedViewController

class PushedViewController: UIViewController {
    @IBOutlet weak var pushedLabel: UILabel!
    @IBOutlet weak var pushedImage: UIImageView!
    var selectedImage: UIImage?
    var selectedText: String?
    override func viewDidLoad() {
        super.viewDidLoad()
        //vc?.pushedImage vc?.pushedLabel are not nil
        pushedImage.image = selectedImage
        pushedLabel.text = selectedText
    }
}

Answer 3

UI组件尚未初始化，因此您无法在初始化控制器后立即访问它们。

我建议您在PushedViewController中有一个局部变量来存储图像和文本，然后在viewDidLoad中分配它们。

赞：

class PushedViewController: UIViewController {
    //..
    var image:UIImage?
    var text:String?
    //..
    override viewDidLoad() {
        super.viewDidLoad()
        //..
        if let image = self.image {
            self.imageView.image = image
        }
        if let text = self.text {
            self.label.text = text
        }
        //..
    }
    //..
}

然后从推动控制器的位置设置这些属性：

func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
    guard let vc = storyboard?.instantiateViewController(withIdentifier: "PushedViewController") as? PushedViewController else { return }
    // Assign the properties here
    vc.image = UIImage(named: imagesArray[indexPath.row])
    vc.text = textsArray[indexPath.row]
    self.navigationController?.pushViewController(vc, animated: true)
}

按下ViewController时无法传输图像

3 个答案: