获取子视图高度以估计另一个视图高度

Question

您好，我想获取子视图的高度来估计 detailUIView heightAnchor。在 detailUIView 中，我有 4 个使用自动约束（以编程方式）布局的标签，我想获取视图高度，以便我可以估计 detailUIView。在函数 estimateCardHeight 中，我正在迭代所有子视图并尝试获取每个子视图的高度并添加它们，但我得到 0.0。我在这里错过了什么，我无法弄清楚。

class ComicDetailViewController: UIViewController {
    var comicNumber = Int()
    
    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        self.navigationItem.title = "Comic Number: \(comicNumber)"
    }
    let detailUIView = DetailComicUIView()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        view.backgroundColor = .white
        // Do any additional setup after loading the view.
        detailUIView.translatesAutoresizingMaskIntoConstraints = false
        view.addSubview(detailUIView)
        addConstraints()
        print(estimateCardHeight())
    }
   
    public func configure(with viewModel: XKCDTableViewCellVM){
        detailUIView.configure(with: viewModel)
        comicNumber = viewModel.number
        
        
    }
    private func estimateCardHeight() -> CGFloat{
        var allHeight : CGFloat = 0
        for view in detailUIView.subviews{
            allHeight += view.frame.origin.y
        }
       return allHeight
    }
 
    
    private func addConstraints(){
        var constraints = [NSLayoutConstraint]()
        constraints.append(detailUIView.topAnchor.constraint(equalTo: self.view.safeAreaLayoutGuide.topAnchor, constant: 10))
        constraints.append(detailUIView.leftAnchor.constraint(equalTo: self.view.leftAnchor, constant: 20))
        constraints.append(detailUIView.rightAnchor.constraint(equalTo: self.view.rightAnchor, constant: -20))

        constraints.append(detailUIView.heightAnchor.constraint(equalToConstant: self.view.frame.height/3))
        
        NSLayoutConstraint.activate(constraints)
    }

    

}

Answer 1

你不见了view.layoutIfNeeded()

    addConstraints()
    view.layoutIfNeeded()
    print(estimateCardHeight())

作为apple's saying

使用此方法强制视图立即更新其布局。使用 Auto Layout 时，布局引擎会根据需要更新视图的位置以满足约束的变化。

如果布局更新未决，则立即布局子视图。

---

我猜：

估计高度的方法，

   private func estimateCardHeight() -> CGFloat{
        var allHeight : CGFloat = 0
        for view in detailUIView.subviews{
            allHeight += view.frame.size.height
            // allHeight += view.frame.origin.y
        }
       return allHeight
    }

Answer 2

实现它的另一种方法。

 override func viewDidLayoutSubviews() {
    super.viewDidLayoutSubviews()
    print(estimateCardHeight())
}

viewDidLayoutSubviews()

调用以通知视图控制器它的视图刚刚布置了它的子视图。