在目前阶段，SwiftUI 很难独立开发一款功能强大的 App，还是需要与 UIKit 一起合作，借助 UIKit 成熟完善的知识体系，二者相互嵌套形成混合开发。

UIKit in SwiftUI

UIViewRepresentable

• 要使 UIView 在 SwiftUI 中可用，需要用UIViewRepresentable对 UIView 进行包装。
• UIViewRepresentable中主要有两个方法需要实现：
  • makeUIView：创建View。
  • updateUIView：根据条件和业务逻辑设置View的状态。
• 案例一

import SwiftUI
import UIKit

struct ActivityIndicator: UIViewRepresentable {
    var isAnimating: Bool
    
    func makeUIView(context: Context) -> UIActivityIndicatorView {
        let v = UIActivityIndicatorView()
        v.color = .orange
        return v
    }
    
    func updateUIView(_ uiView: UIActivityIndicatorView, context: Context) {
        if isAnimating {
            uiView.startAnimating()
        } else {
            uiView.stopAnimating()
        }
    }
}


struct ContentView : View {
    
    var isAnimating: Bool = true  
      
    var body: some View {
        ActivityIndicator(isAnimating: isAnimating)
    }
}

• 案例二

import UIKit
import SwiftUI
import MapKit

struct Map: UIViewRepresentable {
    
    var locationManager:CLLocationManager = CLLocationManager()
    
    func setupManager(){
        
        locationManager.desiredAccuracy = kCLLocationAccuracyBest  
        locationManager.requestWhenInUseAuthorization()
        locationManager.requestAlwaysAuthorization()
    }
    
    func makeUIView(context: Context) -> MKMapView {
        
        self.setupManager() 
       
        let map = MKMapView(frame: UIScreen.main.bounds)
        map.showsUserLocation = true    
        map.userTrackingMode = .followWithHeading 
        return map
        
    }
    
    func updateUIView(_ uiView: MKMapView, context: Context) {
        
    }
}

struct ContentView : View {
    
    var body: some View {
        Map()
    }
}

• 案例三

// 定义一个类负责实现代理
class TextFieldDelegate: NSObject, UITextFieldDelegate {
        
    func textFieldDidBeginEditing(_ textField: UITextField) {
        print("开始编辑")
    }
}

// 定义UIViewRepresentable
struct MyTextField: UIViewRepresentable {
    
    var text: String
    var placeholder: String  
    private let delegate = TextFieldDelegate()
    
    func makeUIView(context: UIViewRepresentableContext<MyTextField>) -> UITextField {
        
        let tmpView = UITextField()
        tmpView.text = text
        tmpView.borderStyle = .roundedRect
        tmpView.placeholder = placeholder
        tmpView.delegate = delegate
        return tmpView
    }
    
    func updateUIView(_ uiView: UITextField, context: UIViewRepresentableContext<MyTextField>) {
    }
}

// SwiftUI使用
struct ContentView : View {
    
    var body: some View {        
        MyTextField(text: "", placeholder: "请输入内容").frame(height: 40).padding()
    }
}

• 如果要桥接 UIKit 的数据绑定（Delegate，Target/Action），需要使用Coordinator进行协调。

import SwiftUI
import UIKit

// 自定义个SegmentControl控件
struct SegmentControl: UIViewRepresentable {
    
    @Binding var selectedSegmentIndex: Int

    // 下面两个方法都是和 UIKit 相关
    func makeUIView(context: Context) -> UISegmentedControl {
        
        let segmentControl = UISegmentedControl()
        segmentControl.insertSegment(withTitle: "红", at: 0, animated: true)
        segmentControl.insertSegment(withTitle: "黄", at: 1, animated: true)
        segmentControl.insertSegment(withTitle: "蓝", at: 2, animated: true)
        segmentControl.selectedSegmentIndex = selectedSegmentIndex
        
        // 注意这里的参数，与Coordinator有关
        segmentControl.addTarget(
            context.coordinator,
            action: #selector(Coordinator.updateCurrentPage(sender:)),
            for: .valueChanged)

        return segmentControl
    }

    func updateUIView(_ uiView: UISegmentedControl, context: Context) {
        uiView.selectedSegmentIndex = selectedSegmentIndex
    }

    // 协议的方法之一，返回一个协调器
    func makeCoordinator() -> Coordinator {
        Coordinator(self)
    }

    // 自定义协调器，UIKit与SwiftUI交互的地方
    class Coordinator: NSObject {
        var control: SegmentControl
        
        init(_ control: SegmentControl) {
            self.control = control
        }
        
        @objc func updateCurrentPage(sender: UISegmentedControl) {
            control.selectedSegmentIndex = sender.selectedSegmentIndex
        }
    }
}

struct ContentView : View {
    
    @State private var selectedSegmentIndex: Int = 1
    
    var body: some View {
        SegmentControl(selectedSegmentIndex: $selectedSegmentIndex)
    }
}

UIViewControllerRepresentable

• 要使 UIViewController 在 SwiftUI 中可用，需要用UIViewControllerRepresentable对 UIViewController 进行包装。
• UIViewControllerRepresentable中主要有两个方法需要实现：
  • makeUIViewController：创建UIViewController。
  • updateUIViewController：根据条件和业务逻辑设置UIViewController的状态。
• 案例

import SwiftUI
import UIKit

struct NavigationViewController: UIViewControllerRepresentable {
    
    var vc: UIViewController
    var title: String

    func makeUIViewController(context: Context) -> UINavigationController {
        
        let nvc = UINavigationController(rootViewController: vc)  
        return nvc
    }

    func updateUIViewController(_ navigationController: UINavigationController, context: Context) {
         
        navigationController.viewControllers[0].title = title        
    }
}


struct ContentView : View {
    
    var body: some View {        
        NavigationViewController(vc: UIViewController(), title: "UIViewControllerRepresentable")
    }
}

SwiftUI in UIKit

SwiftUI 中的 View 需要使用UIHostingController包装以后才可以给 UIKit 使用。

UIHostingController

在开发 iOS 项目章节已经分析过启动流程，就是通过UIHostingController包装 ContentView，然后赋值给window.rootViewController。

// 可以是复杂的ContentView
let vc = UIHostingController(rootView: ContentView())

// 也可以时简单的Text等其他View
let vc = UIHostingController(rootView: Text("Hello SwiftUI"))