Flutter学习笔记-与原生(iOS swift)交互_flutter调用ios原生几种通信方法

需求描述：需要从原生工程里面获取到设备的唯一标识，然后传到flutter模块里面去。

基本原理：Flutter使用了一个灵活的系统，允许您调用特定平台的API，无论在Android上的Java或Kotlin代码中，还是iOS上的ObjectiveC或Swift代码中均可用。Flutter平台特定的API支持不依赖于代码生成，而是依赖于灵活的消息传递的方式：

• 应用的Flutter部分通过平台通道（platform channel）将消息发送到其应用程序的所在的宿主（iOS或Android）。
• 宿主监听的平台通道，并接收该消息。然后它会调用特定于该平台的API（使用原生编程语言） - 并将响应发送回客户端，即应用程序的Flutter部分。

使用平台通道在客户端（Flutter UI）和宿主（平台）之间传递消息，如下图所示：

• 消息和响应是异步传递的，以确保用户界面保持响应(不会挂起)。

• Flutter与原生的交互可以使用 BasicChannel、MethodChannel、EventChannel 三种：

• 1、BasicMessageChannel: 用于传递数据。Flutter与原生项目的资源是不共享的，可以通过BasicMessageChannel来获取Native项目的图标等资源。

• 2、MethodChannel: 传递方法调用。Flutter主动调用Native的方法，并获取相应的返回值。比如获取系统电量，发起Toast等调用系统API，可以通过这个来完成。

• 3、EventChannel: 传递事件。这里是Native将事件通知到Flutter。比如Flutter需要监听网络情况，这时候MethodChannel就无法胜任这个需求了。EventChannel可以将Flutter的一个监听交给Native，Native去做网络广播的监听，当收到广播后借助EventChannel调用Flutter注册的监听，完成对Flutter的事件通知。

本需求使用MethodChannel的方式进行flutter与原生的通信

一、 iOS原生端，可以使用苹果提供的KeychainItemWrapper类，保存生成的唯一标识，作为设备的唯一标识（由于安全问题，设备的唯一码已经拿不到了）。由于KeychainItemWrapper类是用OC语言实现的，所以还存在OC和swift混编的过程。

在swift项目中，新建OC类，Xcode会提示是否创建桥接文件，选择创建桥接文件，然后在桥接文件里面引入swift要使用的OC类的头文件，就可以实现OC和swift的混编了。

• KeychainItemWrapper类的代码如下：

KeychainItemWrapper.h

/*
     File: KeychainItemWrapper.h
 Abstract: 
 Objective-C wrapper for accessing a single keychain item.
 
  Version: 1.2
 
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*/

/*
    
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