Question

我正在尝试将类型为string的新闻ID传递给第二个VC并从Realm加载基于它的对象。当我调试时，我发现准备segue正确地将detailNewsVC.newsID设置为我的新闻项的主键，但第二个VC没有收到它。对此有何帮助？

检查我做了：

确保详细VC标识符正确
detailNewsVC.newsID正确设置了新闻ID。这是为了确保领域正确发送新闻ID并且工作正常。
将VC 2中的viewDidLoad更改为viewWillLoad ..只是为了确保之前没有加载第二个vc，但是没有运气。
重新启动xcode
使用实际的新闻主键替换VC 2中的newsID，并正确地提取相关新闻。我认为罪魁祸首是VC2属性：当调用segue准备时，newsID没有更新。

准备segue的第一个VC代码：

extension HomeVC: UICollectionViewDelegate {

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {


    if segue.identifier == SegueIdentifier.gotodetail.rawValue, let sendNewsID = sender as? String {

        let navVC = segue.destination as? UINavigationController

        let detailNewsVC = navVC?.viewControllers.first as! DetailNewsVC

        detailNewsVC.newsID = sendNewsID
        print("Detail News ID = \(detailNewsVC.newsID)")
    }


}

  func collectionView(_ collectionView: UICollectionView, didSelectItemAt     indexPath: IndexPath) {


    let newsID = newsArray[indexPath.row].newsId

    performSegue(withIdentifier: SegueIdentifier.gotodetail.rawValue, sender: newsID)

}



}

第二个VC代码：

class DetailNewsVC: UIViewController {

@IBOutlet private weak var scrollView: UIScrollView!
@IBOutlet private weak var newsTitle: UILabel!
@IBOutlet private weak var newsImage: UIImageView!
@IBOutlet private weak var newsDescription: UILabel!

var newsID = ""

override func viewDidLoad() {
    super.viewDidLoad()

    let realm = try! Realm()

    print("News ID: \(newsID)")
    guard let news = realm.object(ofType: News.self, forPrimaryKey: newsID as AnyObject) else {
        print("Cannot load news")
        return
    }

    print(news)

    newsTitle.text = news.newsTitle

    if let url = URL(string: news.urlToImage), let data = try? Data.init(contentsOf: url) {

        newsImage.image = UIImage(data: data)

    }

    newsDescription.text = news.newsDescription

}


}

Answer 1

将准备功能移出扩展程序并将其放入HomeVC。根据Apple的Swift Guide扩展无法覆盖现有功能。

扩展程序可以为类型添加新功能，但它们无法覆盖现有功能。

Apple Developer Guide

Answer 2

很难说出UIKit调用UIViewController方法的顺序，但是在你有机会设置viewDidLoad的值之前，可能会调用newsID。 1}}。

以下内容可能有些过分，但它会保证在viewDidLoad期间更新观看次数，或者在事后设置newsID后更新：

class DetailNewsVC: UIViewController {

    @IBOutlet private weak var scrollView: UIScrollView!
    @IBOutlet private weak var newsTitle: UILabel!
    @IBOutlet private weak var newsImage: UIImageView!
    @IBOutlet private weak var newsDescription: UILabel!

    public var newsID = "" {
        didSet {
            updateUIForNews()
        }
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        updateUIForNews() 
    }

    private func updateUIForNews() {
        guard !newsID.isEmpty else {
            return
        }

        let realm = try! Realm()

        print("News ID: \(newsID)")
        guard let news = realm.object(ofType: News.self, forPrimaryKey: newsID as AnyObject) else {
            print("Cannot load news")
            return
        }

        print(news)

        newsTitle.text = news.newsTitle

        if let url = URL(string: news.urlToImage), let data = try? Data.init(contentsOf: url) {

            newsImage.image = UIImage(data: data)

        }

        newsDescription.text = news.newsDescription
    }
}

iOS Swift - 准备segue后属性不更新

2 个答案: