嵌入在 UIViewController 中的 UIHostingController - 如何从外部更新 @State？

Question

我正在使用 UIHostingController 将 ContentView 嵌入到 ViewController 中。当按下“更改名称”按钮时，我想更改ContentView 的name 的名称。这是我的代码：

class ViewController: UIViewController {

    var contentView: ContentView? /// keep reference to ContentView
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        view.backgroundColor = UIColor.secondarySystemBackground
        
        /// add the button
        let button = UIButton()
        button.frame = CGRect(x: 50, y: 50, width: 200, height: 100)
        button.setTitle("Change name", for: .normal)
        button.setTitleColor(.blue, for: .normal)
        button.addTarget(self, action: #selector(handleTap), for: .touchUpInside)
        view.addSubview(button)
        
        /// add the SwiftUI ContentView
        let contentView = ContentView()
        let hostingController = UIHostingController(rootView: contentView)
        self.contentView = contentView
        
        addChild(hostingController)
        view.insertSubview(hostingController.view, at: 0)
        hostingController.view.frame = CGRect(x: 0, y: 400, width: view.bounds.width, height: view.bounds.height - 400)
        hostingController.view.autoresizingMask = [.flexibleWidth, .flexibleHeight]
        hostingController.didMove(toParent: self)
    }
    
    @objc func handleTap() {
        contentView?.updateLastCardName(name: "Updated name") /// update the name
    }
}

struct ContentView: View {
    @State var name = "Name"

    var body: some View {
        Text(name)
    }

    func updateLastCardName(name: String) {
        print("updating to \(name)")
        self.name = name /// but it's not updating!
    }
}

结果：

问题是，即使 func updateLastCardName(name: String) { 被调用，当我设置 self.name = name 时也没有任何变化。 Text 继续显示“名称”，而不是“更新的名称”。

我读过@State should be local，所以我尝试使用updateLastCardName 函数来解决这个问题。但是，它不起作用。我的方法错了吗？

如何从ViewController 更新ContentView 的name？

Answer 1

var contentView: ContentView? /// keep reference to ContentView

这是错误的假设，因为ContentView 是一个结构，即。价值，所以您保留副本而不是参考。

相反，我们应该使用视图模型类的实例作为从 UIKit 到 SwiftUI 通信的参考。在下面找到带有方法演示的修改代码。

使用 Xcode 12.4 / iOS 14.4 测试

class ViewModel: ObservableObject {
    @Published var name = "Name"
}

class ViewController: UIViewController {

    private var vm: ViewModel!

    override func viewDidLoad() {
        super.viewDidLoad()

        view.backgroundColor = UIColor.secondarySystemBackground

        /// add the button
        let button = UIButton()
        button.frame = CGRect(x: 50, y: 50, width: 200, height: 100)
        button.setTitle("Change name", for: .normal)
        button.setTitleColor(.blue, for: .normal)
        button.addTarget(self, action: #selector(handleTap), for: .touchUpInside)
        view.addSubview(button)

        /// add the SwiftUI ContentView
        self.vm = ViewModel()
        let contentView = ContentView(vm: self.vm)
        let hostingController = UIHostingController(rootView: contentView)

        addChild(hostingController)
        view.insertSubview(hostingController.view, at: 0)
        hostingController.view.frame = CGRect(x: 0, y: 400, width: view.bounds.width, height: view.bounds.height - 400)
        hostingController.view.autoresizingMask = [.flexibleWidth, .flexibleHeight]
        hostingController.didMove(toParent: self)
    }

    @objc func handleTap() {
        vm.name = "Updated name" /// update the name
    }
}

struct ContentView: View {
    @ObservedObject var vm: ViewModel

    var body: some View {
        Text(vm.name)
    }
}