当然，关于Flutter自定义功能插件flutter_customs（请注意，flutter_customs并非一个官方或广泛认知的Flutter插件，这里我将创建一个假设的插件案例来展示如何创建和使用自定义Flutter插件）。

创建自定义Flutter插件

1. 插件项目结构

首先，我们需要创建一个Flutter插件项目。使用以下命令：

flutter create --template=plugin flutter_customs

这将创建一个名为flutter_customs的插件项目，其结构大致如下：

flutter_customs/
├── example/
│   └── ... (Flutter应用示例)
├── lib/
│   ├── flutter_customs.dart (插件主文件)
│   └── ... (其他插件代码)
├── ios/
│   └── Classes/
│       └── FlutterCustomsPlugin.m (iOS平台代码)
├── android/
│   └── src/
│       └── main/
│           └── kotlin/
│               └── com/
│                   └── example/
│                       └── flutter_customs/
│                           └── FlutterCustomsPlugin.kt (Android平台代码)
└── ... (其他配置文件)

2. 实现插件功能

假设我们要实现一个简单的功能：从原生平台（iOS和Android）获取设备信息，并将其传递给Flutter。

iOS 平台实现

在ios/Classes/FlutterCustomsPlugin.m中：

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

@interface FlutterCustomsPlugin : NSObject<FlutterPlugin>
@end

@implementation FlutterCustomsPlugin
+ (void)registerWithRegistrar:(NSObject<FlutterPluginRegistrar>*)registrar {
    FlutterMethodChannel* channel = [FlutterMethodChannel methodChannelWithName:@"flutter_customs" binaryMessenger:[registrar messenger]];
    FlutterCustomsPlugin* instance = [[FlutterCustomsPlugin alloc] init];
    [channel setMethodCallHandler:[instance methodCallHandler]];
}

- (FlutterMethodCallHandler)methodCallHandler {
    return ^(FlutterMethodCall* call, FlutterResult result) {
        if ([@"getDeviceInfo" isEqualToString:call.method]) {
            NSString *deviceName = [[UIDevice currentDevice] name];
            NSString *systemVersion = [[UIDevice currentDevice] systemVersion];
            NSDictionary *deviceInfo = @{
                @"deviceName": deviceName,
                @"systemVersion": systemVersion
            };
            result(deviceInfo);
        } else {
            result(FlutterMethodNotImplemented);
        }
    };
}
@end

Android 平台实现

在android/src/main/kotlin/com/example/flutter_customs/FlutterCustomsPlugin.kt中：

package com.example.flutter_customs

import android.os.Build
import android.os.Bundle
import androidx.annotation.NonNull
import io.flutter.embedding.engine.plugins.FlutterPlugin
import io.flutter.embedding.engine.plugins.activity.ActivityAware
import io.flutter.embedding.engine.plugins.activity.ActivityPluginBinding
import io.flutter.plugin.common.MethodCall
import io.flutter.plugin.common.MethodChannel
import io.flutter.plugin.common.MethodChannel.MethodCallHandler
import io.flutter.plugin.common.MethodChannel.Result

class FlutterCustomsPlugin: FlutterPlugin, MethodCallHandler, ActivityAware {
    private lateinit var channel: MethodChannel
    private var activityBinding: ActivityPluginBinding? = null

    override fun onAttachedToEngine(@NonNull flutterPluginBinding: FlutterPluginBinding) {
        channel = MethodChannel(flutterPluginBinding.binaryMessenger, "flutter_customs")
        channel.setMethodCallHandler(this)
    }

    override fun onMethodCall(@NonNull call: MethodCall, @NonNull result: Result) {
        if (call.method == "getDeviceInfo") {
            val deviceInfo = mapOf(
                "deviceName" to android.os.Build.MODEL,
                "systemVersion" to android.os.Build.VERSION.RELEASE
            )
            result.success(deviceInfo)
        } else {
            result.notImplemented()
        }
    }

    override fun onDetachedFromEngine(@NonNull binding: FlutterPluginBinding) {
        channel.setMethodCallHandler(null)
    }

    override fun onAttachedToActivity(binding: ActivityPluginBinding) {
        activityBinding = binding
    }

    override fun onDetachedFromActivityForConfigChanges() {
        activityBinding = null
    }

    override fun onReattachedToActivityForConfigChanges(binding: ActivityPluginBinding) {
        activityBinding = binding
    }

    override fun onDetachedFromActivity() {
        activityBinding = null
    }
}

3. 在Flutter中使用插件

在lib/flutter_customs.dart中定义插件接口：

import 'package:flutter/services.dart';

class FlutterCustoms {
  static const MethodChannel _channel = MethodChannel('flutter_customs');

  static Future<Map<String, String>> getDeviceInfo() async {
    final Map<String, String> deviceInfo = await _channel.invokeMethod('getDeviceInfo');
    return deviceInfo;
  }
}

在Flutter应用中使用该插件：

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

void main() {
  runApp(MyApp());
}

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  Map<String, String>? deviceInfo;

  @override
  void initState() {
    super.initState();
    _getDeviceInfo();
  }

  Future<void> _getDeviceInfo() async {
    String? error;
    deviceInfo = await FlutterCustoms.getDeviceInfo().catchError((e) {
      error = e.toString();
    });

    if (error == null) {
      setState(() {});
    }
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: const Text('Flutter Customs Plugin Demo'),
        ),
        body: Center(
          child: deviceInfo != null
              ? Column(
                  mainAxisAlignment: MainAxisAlignment.center,
                  children: <Widget>[
                    Text('Device Name: ${deviceInfo!['deviceName']}'),
                    Text('System Version: ${deviceInfo!['systemVersion']}'),
                  ],
                )
              : CircularProgressIndicator(),
        ),
      ),
    );
  }
}

这个示例展示了如何创建一个简单的Flutter插件来获取设备信息，并在Flutter应用中使用它。希望这对你有所帮助！如果你有更多具体需求或问题，请随时提出。