1. Dart部分

1.1. 新建native.dart，flutter混合原生view界面

import 'package:flutter/material.dart';
import 'package:flutter/services.dart';

/// flutter混合原生view
class CMNativePage extends StatelessWidget {
  const CMNativePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return const Scaffold(
      body: Center(
        child: IOSCompositionWidget()
      ),
    );
  }
}

class IOSCompositionWidget extends StatelessWidget {
  const IOSCompositionWidget({super.key});

  @override
  Widget build(BuildContext context) {
    // This is used in the platform side to register the view.
    const String viewType = 'custom_platform_view';
    // Pass parameters to the platform side.
    final Map<String, dynamic> creationParams = {'content': 'Flutter传给IOSView的参数'};

    return UiKitView(
      viewType: viewType,
      creationParams: creationParams,
      creationParamsCodec: const StandardMessageCodec(),
    );
  }
}

1.2. 在main.dart的路由表中，增加nativePage。供iOS原生进行跳转

'nativePage': (settings, uniqueId) {
      return PageRouteBuilder<dynamic>(
          settings: settings,
          pageBuilder: (_, __, ___) {
            return const CMNativePage();
          });
    },

2. iOS部分

2.1. 新建FLNativeView和FLNativeViewFactory
FLNativeView.h

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

NS_ASSUME_NONNULL_BEGIN

@interface FLNativeViewFactory : NSObject <FlutterPlatformViewFactory>
- (instancetype)initWithMessenger:(NSObject<FlutterBinaryMessenger>*)messenger;
@end

@interface FLNativeView : NSObject <FlutterPlatformView>

@property (nonatomic, strong) UILabel *label;

- (instancetype)initWithFrame:(CGRect)frame viewIdentifier:(int64_t)viewId arguments:(id _Nullable)args binaryMessenger:(NSObject<FlutterBinaryMessenger>*)messenger;

@end

NS_ASSUME_NONNULL_END

FLNativeView.m

#import "FLNativeView.h"

@implementation FLNativeViewFactory {
  NSObject<FlutterBinaryMessenger> *_messenger;
}

- (instancetype)initWithMessenger:(NSObject<FlutterBinaryMessenger>*)messenger {
  self = [super init];
  if (self) {
    _messenger = messenger;
  }
  return self;
}

- (NSObject<FlutterPlatformView>*)createWithFrame:(CGRect)frame viewIdentifier:(int64_t)viewId arguments:(id _Nullable)args {
  return [[FLNativeView alloc] initWithFrame:frame viewIdentifier:viewId arguments:args binaryMessenger:_messenger];
}

-(NSObject<FlutterMessageCodec> *)createArgsCodec{
    return [FlutterStandardMessageCodec sharedInstance];
}

@end

@implementation FLNativeView

- (instancetype)initWithFrame:(CGRect)frame viewIdentifier:(int64_t)viewId arguments:(id _Nullable)args binaryMessenger:(NSObject<FlutterBinaryMessenger>*)messenger {
  if (self = [super init]) {
      self.label = [UILabel new];
      self.label.textColor = [UIColor redColor];
      NSDictionary *dict = (NSDictionary *)args;
      NSString *textValue = dict[@"content"];
      self.label.text = [NSString stringWithFormat:@"我是iOS View，传值：%@", textValue];
  }
  return self;
}

- (nonnull UIView *)view {
    return self.label;
}

@end

2.2. 其中FLNativeViewFactory中的createArgsCodec方法一定不能遗漏，否则会导致传值不成功。类型也一定要和Dart部分的native.dart->IOSCompositionWidget-> UiKitView-> creationParamsCodec保持一致。否则会导致崩溃：
2.3. 修改AppDelegate.h：修改继承为FlutterAppDelegate，并删除window属性，因为FlutterAppDelegate中已经自带window属性

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

@interface AppDelegate : FlutterAppDelegate

@end

2.4. 在AppDelegate.m中引入头文件

#import "FLNativeView.h"
#import "GeneratedPluginRegistrant.h"

2.5. 在AppDelegate.m中注册插件，注意这里有非常大的坑。官方文档中是这么写的：

- (BOOL)application:(UIApplication *)application
    didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
  [GeneratedPluginRegistrant registerWithRegistry:self];
  NSObject<FlutterPluginRegistrar>* registrar = [self registrarForPlugin:@"plugin-name"];
  FLNativeViewFactory* factory = [[FLNativeViewFactory alloc] initWithMessenger:registrar.messenger];
  [[self registrarForPlugin:@"<plugin-name>"] registerViewFactory:factory withId:@"<platform-view-type>"];
  return [super application:application didFinishLaunchingWithOptions:launchOptions];
}

这样写本身是没问题的，但是在引入flutter_boost的情况下，就不能这么写了！正确的做法是，需要等flutter_boost初始化完成后，用FlutterEngine对插件进行初始化！代码如下：

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    // 初始化window
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    ViewController *vc = [ViewController new];
    UINavigationController *navigation = [[UINavigationController alloc] initWithRootViewController:vc];
    self.window.rootViewController = navigation;
    [self.window makeKeyAndVisible];
    self.window.backgroundColor = [UIColor whiteColor];

    // 初始化FlutterBoost
    BoostDelegate *delegate = [BoostDelegate sharedInstance];
    delegate.navigationController = (UINavigationController *)self.window.rootViewController;
    [[FlutterBoost instance] setup:application delegate:delegate callback:^(FlutterEngine *engine) {
        // 初始化Flutter内嵌iOSView插件
        NSObject<FlutterPluginRegistrar> *registrar = [engine registrarForPlugin:@"custom_platform_view_plugin"];
        FLNativeViewFactory *factory = [[FLNativeViewFactory alloc] initWithMessenger:registrar.messenger];
        [registrar registerViewFactory:factory withId:@"custom_platform_view"];
    }];
    
    return YES;
}

如果按照官方相同的写法，跳转过去会一直是一个空白页面，不会有原生组件嵌入其中。这个问题，我查了很久网上都没有相关资料，希望能帮到后面遇到坑的人~

其中withId:xxx，xxx代表控件的ID，需要和Dart部分的IOSCompositionWidget中的viewType保持一致。命名为：custom_platform_view

其中registrarForPlugin:xxx，xxx代表插件的ID。命名为：custom_platform_view_plugin

2.6. 在ViewController.m测试页面中，增加跳转Flutter页面的按钮和跳转方法

- (void)viewDidLoad {
    [super viewDidLoad];
    self.view.backgroundColor = [UIColor whiteColor];
  
    UIButton *pushFlutterNativePageButton = [UIButton buttonWithType:UIButtonTypeSystem];
    pushFlutterNativePageButton.frame = CGRectMake(100, 300, 300, 100);
    [pushFlutterNativePageButton setTitleColor:[UIColor blueColor] forState:UIControlStateNormal];
    [pushFlutterNativePageButton setTitle:@"跳转到Flutter混合原生view界面" forState:UIControlStateNormal];
    [pushFlutterNativePageButton addTarget:self action:@selector(pushFlutterNativePage) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:pushFlutterNativePageButton];
    
}

// 跳转Flutter混合原生view界面
- (void)pushFlutterNativePage{
    FlutterBoostRouteOptions *options = [FlutterBoostRouteOptions new];
    options.pageName = @"nativePage";
    options.arguments = @{@"animated": @(YES)};
    options.completion = ^(BOOL completion) {
    };
    [[FlutterBoost instance] open:options];
    options.onPageFinished = ^(NSDictionary *dic) {
        NSLog(@"%@", dic);
    };
}