Flutter关于FlutterEngineGroup的使用

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1.FlutterEngineGroup

FlutterEngineGroup 是一个用于管理多个 FlutterEngine 实例的类。当你的应用需要同时运行多个 Flutter 引擎时，可以使用 FlutterEngineGroup 来有效地管理和共享资源，例如平台的插件注册和插件的通信管道。

2.FlutterEngineGroup主要用途

• 共享插件注册：在多个 Flutter 引擎之间共享插件注册，避免重复注册相同的插件。
• 优化性能：通过共享插件注册和通信管道，减少资源消耗，提高应用性能。
• 简化管理：提供一个集中的地方来管理多个 Flutter 引擎的生命周期。

3.FlutterEngineGroup适用场景

• 混合路由栈：Flutter 和 native 互跳，即 native -> Flutter -> native -> Flutter
• 模块化：使用多个 Flutter 实例，每个实例各自维护路由栈、UI 和应用状态.
• 多视图：多个Flutter View同时集成在同一个页面上，且同时显示.

4.FlutterEngineGroup示例

本示例演示多视图情况下，两个Flutter View同时显示在同一个页面中。

AppDelegate.swift

import UIKit
import Flutter

@main
class AppDelegate: UIResponder, UIApplicationDelegate {

    static let FlutterEngineMaxNum = 2
    let flutterEngineGroup = FlutterEngineGroup(name: "multiple-flutters", project: nil)
    lazy var flutterEngines:[FlutterEngine] = Array()
    
    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
        // Override point for customization after application launch.
        for _ in 0..<AppDelegate.FlutterEngineMaxNum {
            let flutterEngine = flutterEngineGroup.makeEngine(withEntrypoint: "main", libraryURI: nil)
            flutterEngine.run()
            flutterEngines.append(flutterEngine)
        }
        return true
    }
    
    // MARK: UISceneSession Lifecycle
    func application(_ application: UIApplication, configurationForConnecting connectingSceneSession: UISceneSession, options: UIScene.ConnectionOptions) -> UISceneConfiguration {
        // Called when a new scene session is being created.
        // Use this method to select a configuration to create the new scene with.
        return UISceneConfiguration(name: "Default Configuration", sessionRole: connectingSceneSession.role)
    }

    func application(_ application: UIApplication, didDiscardSceneSessions sceneSessions: Set<UISceneSession>) {
        // Called when the user discards a scene session.
        // If any sessions were discarded while the application was not running, this will be called shortly after application:didFinishLaunchingWithOptions.
        // Use this method to release any resources that were specific to the discarded scenes, as they will not return.
    }
}

UIViewController.swift

import UIKit
import Flutter

class ViewController: UIViewController {
    
    var flutterViewControllers:[FlutterViewController] = []

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
    }
    
    @IBAction func showFlutterViewEvent()  {
        //showSingleFlutterView()
        showTwoFlutterView()
    }
    
    @IBAction func removeFlutterViewsEvent()  {
        
        for item in flutterViewControllers {
            item.view.removeFromSuperview()
        }
        
        flutterViewControllers.removeAll();
    }
    
    func showTwoFlutterView() {
        
        guard flutterViewControllers.isEmpty else {
            return
        }
        
        let  viewWidth = CGRectGetWidth(self.view.frame)
        
        let flutterEngines = (UIApplication.shared.delegate as! AppDelegate).flutterEngines
        
        for engine in flutterEngines {
            let flutterViewController = FlutterViewController(engine: engine, nibName: nil, bundle: nil)

            self.view.addSubview(flutterViewController.view)
            self.view.bringSubviewToFront(flutterViewController.view)
            flutterViewControllers.append(flutterViewController)
            
        }

        flutterViewControllers[0].view.frame = CGRect(x: 0, y: 250, width: viewWidth/3, height: 500)
        flutterViewControllers[1].view.frame = CGRect(x: viewWidth * 2/3, y: 250, width: viewWidth/3, height: 500)
    }
    
    func showSingleFlutterView() {
        guard let flutterEngine = (UIApplication.shared.delegate as! AppDelegate).flutterEngines.first else { return }
        
        let flutterViewController = FlutterViewController(engine: flutterEngine, nibName: nil, bundle: nil)
        let navigationController = UINavigationController(rootViewController: flutterViewController)
        navigationController.navigationBar.topItem?.rightBarButtonItem = UIBarButtonItem(barButtonSystemItem: .stop, target: self, action: #selector(dismissFlutterViewController))
        present(navigationController, animated: true, completion: nil)
    }
    
    @objc func dismissFlutterViewController() {
        dismiss(animated: true, completion: nil)
   }
}