SwiftUI -- 包装UIKit控件

创建一个 struct 遵循 UIViewRepresentable 协议，实现 makeUIView, updateUIView 方法，将 UIKit 的控件在 makeUIView 方法中返回

import SwiftUI
import UIKit

struct LoadingIndicatorView: UIViewRepresentable {
    
    func makeUIView(context: UIViewRepresentableContext<LoadingIndicatorView>) -> UIView {
        let view = UIActivityIndicatorView(style: .medium)
        view.startAnimating()
        return view
    }
    
    func updateUIView(_ uiView: UIView, context: UIViewRepresentableContext<LoadingIndicatorView>) {
        
    }
    
}