iOS项目开发：集成flutter模块找不到自定义插件

我写了一个在纯flutter环境下可以正常运行的插件。然而，将flutter项目集成到iOS项目后，使用Xcode启动iOS项目并进入flutter界面。 ，但是报了如下错误：

Unhandled Exception: MissingPluginException(No implementation found for method getPlatformVersion on channel koolearn_test)

代码如下：

AppDelegate:

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    self.window.rootViewController = [[ViewController alloc] init];
    self.window.backgroundColor = [UIColor whiteColor];
    [self.window makeKeyAndVisible];
    
    return [super application:application didFinishLaunchingWithOptions:launchOptions];
}

ViewController:

#import ""
#import <Flutter/Flutter.h>

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
}

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
    FlutterViewController* flutterViewController = [[FlutterViewController alloc] init];
    [self presentViewController:flutterViewController animated:false completion:nil];
}

第一次尝试：引入GenegedPluginRegistrant

创建插件工程时，目录自动生成一个示例文件其中包含测试项目补充。打开iOS测试项目，在AppDelegate类中我看到比我写的插件代码多了一行注册代码，所以我肯定是连接到iOS项目了。

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
   
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    self.window.rootViewController = [[ViewController alloc] init];
    self.window.backgroundColor = [UIColor whiteColor];
    [self.window makeKeyAndVisible];

    [GeneratedPluginRegistrant registerWithRegistry:self];

    return [super application:application didFinishLaunchingWithOptions:launchOptions];
}

尝试结果：失败，仍然报上述错误

第二次尝试：将RootViewController设置为FlutterViewController

我在闲鱼博客上看到了一个解决方案，就是将RootViewController设置为FlutterViewController。测试正常，错误解决。但是我们项目的首页是原生页面，所以窗口的rootViewController不能是FlutterViewController。

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    
    // 显示Window
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    [self.window setRootViewController:[[FlutterViewController alloc] initWithNibName:nil bundle:nil]];
    [self.window setBackgroundColor:[UIColor whiteColor]];
    [self.window makeKeyAndVisible];

    [GeneratedPluginRegistrant registerWithRegistry:self];
    
    return [super application:application didFinishLaunchingWithOptions:launchOptions];
}

第三次尝试：引入FlutterEngine

终于在flutter wiki上找到了新的解决方案。创建一个新的FlutterEngine，并让FlutterEngine作为插件的注册对象。问题解决了。 ？