调整UIHostingController约束时SwiftUI View无动画问题求助

问题核心在于UIKit和SwiftUI的动画系统相互独立：你用UIKit的UIView.animate修改约束时，UIHostingController的视图会跟着动，但内部的SwiftUI视图无法感知到这个UIKit层面的动画过程，所以不会同步呈现动画效果。

下面提供两种简单可行的解决方案：

方案一：通过绑定让SwiftUI主动响应动画 #

把容器高度通过绑定传递给SwiftUI视图，让SwiftUI自己处理动画逻辑，和UIKit动画保持同步：

1. 修改MapView，添加绑定属性并关联动画：

struct MapView: View {
    @Binding var containerHeight: CGFloat
    
    var body: some View {
        Text("Hello, World!")
            .frame(maxWidth: .infinity, maxHeight: .infinity)
            .background(Color.blue.opacity(0.3))
            // 监听高度变化，应用对应时长的动画
            .animation(.linear(duration: 2.0), value: containerHeight)
    }
}

2. 在UIViewController中添加ViewModel管理高度状态，同步UIKit和SwiftUI的高度变化：

// 用ObservableObject管理SwiftUI需要的响应式状态
class ViewModel: ObservableObject {
    @Published var mapHeight: CGFloat = 700
}

class ViewController: UIViewController {
    var heightConstraint: NSLayoutConstraint?
    private let viewModel = ViewModel()
    // 懒加载初始化hostingVC，绑定ViewModel的高度属性
    lazy var hostingVC = UIHostingController(rootView: MapView(containerHeight: $viewModel.mapHeight))
    let button = UIButton()
    var isExpanded = true

    override func viewDidLoad() {
        super.viewDidLoad()
        setupHostingVC()
        setupButton()
    }

    private func setupHostingVC() {
        hostingVC.view.backgroundColor = .lightGray
        addChildController(hostingVC)
        hostingVC.view.translatesAutoresizingMaskIntoConstraints = false
        
        heightConstraint = hostingVC.view.heightAnchor.constraint(equalToConstant: viewModel.mapHeight)
        
        NSLayoutConstraint.activate([
            hostingVC.view.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor),
            heightConstraint!,
            hostingVC.view.leadingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.leadingAnchor),
            hostingVC.view.trailingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.trailingAnchor)
        ])
    }

    private func setupButton() {
        button.translatesAutoresizingMaskIntoConstraints = false
        view.addSubview(button)
        button.setTitle("Animation", for: .normal)
        button.backgroundColor = .darkGray
        button.titleLabel?.textColor = .white
        button.addTarget(self, action: #selector(toggleHeight), for: .touchUpInside)
        
        NSLayoutConstraint.activate([
            button.centerXAnchor.constraint(equalTo: view.centerXAnchor),
            button.centerYAnchor.constraint(equalTo: view.centerYAnchor, constant: 100),
            button.widthAnchor.constraint(equalToConstant: 100),
            button.heightAnchor.constraint(equalToConstant: 50)
        ])
    }

    @objc func toggleHeight() {
        let targetHeight: CGFloat = isExpanded ? 200 : 700
        
        // UIKit动画更新约束
        UIView.animate(withDuration: 2.0) {
            self.heightConstraint?.constant = targetHeight
            self.view.layoutIfNeeded()
        }
        
        // SwiftUI动画更新绑定高度，和UIKit动画时长保持一致
        withAnimation(.linear(duration: 2.0)) {
            self.viewModel.mapHeight = targetHeight
        }
        
        isExpanded.toggle()
    }
}

方案二：用GeometryReader让SwiftUI感知布局变化 #

如果不想引入绑定和ViewModel，可以在SwiftUI视图中用GeometryReader捕捉容器尺寸变化，自动触发动画：

只需要修改MapView即可：

struct MapView: View {
    var body: some View {
        GeometryReader { geometry in
            Text("Hello, World!")
                .frame(maxWidth: .infinity, maxHeight: .infinity)
                .background(Color.blue.opacity(0.3))
                // 监听容器高度变化，应用动画
                .animation(.linear(duration: 2.0), value: geometry.size.height)
        }
    }
}

这样当UIHostingController的视图高度通过UIKit动画改变时，GeometryReader会实时捕捉到高度变化，SwiftUI视图就会同步呈现动画效果。

内容的提问来源于stack exchange，提问作者Trieu Nguyen