UIKit

1. UIView 和 CALayer

• UIView继承UIResponder，可以响应事件；
• CALayer用来绘制内容；
• UIView设置表现和位置时，内部实际是对所持有的layer的更改

2. Frame 和 Bounds

• frame.origin设置视图在父视图坐标系中的位置；frame.size设置视图的尺寸
• bounds.origin设置坐标系左上角的坐标(默认(0,0))，子视图随之更改位置；bounds.size设置视图的尺寸但中心点不变

UITabBarController

class TabBarController: UITabBarController, UITabBarControllerDelegate {
    init() {
        super.init(nibName: nil, bundle: nil)
        
        viewControllers = ["1", "2", "3"].map { text in
            ViewController(text: text)
        }
        
        delegate = self
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    func tabBarController(_ tabBarController: UITabBarController, didSelect viewController: UIViewController) {
        print(viewControllers?.firstIndex(of: viewController))
    }
}

class ViewController: UIViewController {
    init(text: String) {
        super.init(nibName: nil, bundle: nil)
        
        let label = UILabel(frame: .init(x: 100, y: 100, width: 100, height: 30))
        label.text = text
        
        view.addSubview(label)
        tabBarItem = UITabBarItem(title: text, image: nil, tag: 0)
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
}

在SwiftUI中使用UIKit的App生命周期

import SwiftUI

@main
struct DemoApp: App {
    @UIApplicationDelegateAdaptor var delegate: AppDelegate
    
    var body: some Scene {
        WindowGroup {
            DemoView()
        }
    }
}

class AppDelegate: UIResponder, UIApplicationDelegate {
    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey : Any]? = nil) -> Bool {
        return true
    }
}