如何在UIKit与SwiftUI混合导航中使@FocusState生效

问题场景 #

项目采用SwiftUI作为视图层、UIKit负责导航，当UIHostingController被UINavigationController管理时，TextField的@FocusState属性包装器完全无法响应（既不能捕获焦点变化，也无法程序化设置焦点），但纯SwiftUI项目中该功能正常。曾尝试用Button包裹TextField模拟聚焦效果，但无法实现程序化触发聚焦。

解决方案 #

方法1：通过UIViewRepresentable桥接UITextField，手动管理焦点 #

直接利用UIKit的第一响应者机制，结合SwiftUI状态同步，绕过SwiftUI焦点系统在UIKit导航下的冲突：

struct FocusableTextField: UIViewRepresentable {
    @Binding var text: String
    @Binding var isFocused: Bool
    let placeholder: String
    
    func makeUIView(context: Context) -> UITextField {
        let textField = UITextField()
        textField.placeholder = placeholder
        textField.borderStyle = .none
        // 同步文本变化到SwiftUI
        textField.addTarget(context.coordinator, action: #selector(Coordinator.textChanged), for: .editingChanged)
        // 同步焦点状态到SwiftUI
        textField.delegate = context.coordinator
        return textField
    }
    
    func updateUIView(_ uiView: UITextField, context: Context) {
        uiView.text = text
        // 根据SwiftUI状态控制第一响应者
        if isFocused != uiView.isFirstResponder {
            isFocused ? uiView.becomeFirstResponder() : uiView.resignFirstResponder()
        }
    }
    
    func makeCoordinator() -> Coordinator {
        Coordinator(self)
    }
    
    class Coordinator: NSObject, UITextFieldDelegate {
        let parent: FocusableTextField
        
        init(_ parent: FocusableTextField) {
            self.parent = parent
        }
        
        @objc func textChanged(_ textField: UITextField) {
            parent.text = textField.text ?? ""
        }
        
        func textFieldDidBeginEditing(_ textField: UITextField) {
            parent.isFocused = true
        }
        
        func textFieldDidEndEditing(_ textField: UITextField) {
            parent.isFocused = false
        }
    }
}

在SwiftUI视图中使用该包装器：

@State private var isFocused: Bool = false

@ViewBuilder
func phoneTextField() -> some View {
    FocusableTextField(
        text: $viewModel.phoneTextfieldNumber,
        isFocused: $isFocused,
        placeholder: "Введите номер"
    )
    .frame(minWidth: 0, maxWidth: .infinity)
    .background(isFocused ? .clear : Resources.Colors.backgroundGrey100.swiftUIColor)
    .cornerRadius(12)
    .overlay(
        RoundedRectangle(cornerRadius: 12)
            .stroke(Resources.Colors.buttonRed100.swiftUIColor, lineWidth: isFocused ? 2 : 0)
    )
    .animation(.default, value: isFocused)
    .onChange(of: isFocused) { newValue in
        print("NEWFOCUS", newValue)
    }
}

方法2：禁用UIHostingController的自动滚动视图调整（可选尝试） #

部分场景下，UINavigationController的滚动视图Insets调整会干扰SwiftUI焦点系统，可在初始化UIHostingController时关闭该特性：

let swiftUIView = YourSwiftUIView()
let hostingController = UIHostingController(rootView: swiftUIView)
hostingController.automaticallyAdjustsScrollViewInsets = false
navigationController.pushViewController(hostingController, animated: true)

方法3：迁移到SwiftUI原生NavigationStack（长期方案） #

如果项目允许，替换UIKit的UINavigationController为SwiftUI的NavigationStack，可彻底避免跨框架的响应链冲突，让@FocusState恢复正常工作。

问题原因 #

当UIHostingController嵌套在UINavigationController中时，UIKit的响应链优先级高于SwiftUI的焦点系统，导致@FocusState无法正确绑定TextField的焦点状态。通过UIViewRepresentable直接操作UITextField的第一响应者，可绕开这一冲突，实现状态同步与程序化聚焦。

内容的提问来源于stack exchange，提问作者Zhenya Taran