iOS和flutter混编FlutterMethodChannel内存泄漏问题
1.前言
移动端原生和flutter模块混编时，少不了要在两个模块之间做通讯的需求。flutter为我们提供了三种交互方式：
BasicMessageChannel：双向通道，iOS和flutter都可以主动向对方传递消息，最简单的传递数据。
MethodChannel：双向通道，使用方式基本和BasicMessageChannel一样，但是高级一些，能够自定义methodName。
EventChannel：用于事件流的发送（event streams), 属于持续性的单向通信, 只能是
iOS端主动调用, 常用于传递原生设备的信息, 状态等, 比如电池电量, 远程通知, 网络状态变化, 手机方向, 重力感应, 定位位置变化等等.
具体如何使用可以点击上方对应的链接查阅，这里不再赘述。本篇主要记录我在使用中遇到得一点问题和疑惑。
2.版本
当前使用的flutter和dart版本如下：
flutter 2.8.1 • channel stable • https://github.com/flutter/flutter.git Framework • revision 77d935af4d (5 weeks ago) • 2021-12-16 08:37:33 -0800 Engine • revision 890a5fca2e Tools • Dart 2.15.1 复制代码
3.功能描述
很简单的一个测试功能：
原生ViewController跳转到flutter模块，（即，present一个FlutterViewController）。
flutter模块点击左上角按钮触发MethodChannel，通知原生调用dismiss方法关闭flutter模块。
具体代码实现如下（只贴主要代码）：
3.1原生代码
为了方便查看对象是否销毁，这里继承一下官方的类，并重写deinit方法。
class CusFlutterViewController: FlutterViewController { override init(engine: FlutterEngine, nibName: String?, bundle nibBundle: Bundle?) { super.init(engine: engine, nibName: nibName, bundle: nibBundle) self.modalPresentationStyle = .fullScreen } required init(coder aDecoder: NSCoder) { super.init(coder: aDecoder) } deinit { debugPrint("deinit \(self)") } } class CusFlutterMethodChannel: FlutterMethodChannel { deinit { debugPrint("deinit \(self)") } } 复制代码当FlutterViewController和FlutterMethodChannel被销毁时，控制台会打印出对应的日志。
创建引擎，创建flutterViewController，methodChannel，并实现回调。
let flutterEngine = FlutterEngine(name: "my flutter engine") flutterEngine.run() GeneratedPluginRegistrant.register(with: flutterEngine); ...省略无关代码 self.flutterVC = CusFlutterViewController.init(engine: flutterEngine, nibName: nil, bundle: nil) self.channel = CusFlutterMethodChannel.init(name: "channel", binaryMessenger: self.flutterVC!.binaryMessenger) self.channel?.setMethodCallHandler { [weak self] handler, block in let method = handler.method switch method { case "exit_flutter_module": self?.dismiss(animated: true, completion: { self?.channel?.setMethodCallHandler(nil) self?.channel = nil self?.flutterVC = nil }) default:() } } self.present(self.flutterVC!, animated: true, completion: nil) 复制代码
3.2 flutter端代码
点击按钮时，通知原生dismiss掉flutter模块
const MethodChannel flutterMethodChannel = MethodChannel('channel'); ...省略无关代码 TextButton( child: const Text("back", style: TextStyle(color: Colors.red),), onPressed: () async { var result = await flutterMethodChannel.invokeMapMethod("exit_flutter_module") ?? {}; debugPrint("$result"); }, ) 复制代码4.发现问题
当运行上述代码，从flutter模块返回原生页面时，发现控制台仅仅只输出了flutterViewController的deinit日志，而flutterMethodChannel的deinit方法并没有被触发。每次重新进入到flutter页面都会再次创建一个新的channel对象，但是返回时析构函数deinit并不会被触发。也就是说我重复N次进入和退出flutter页面时，内存中便创建了N个channel对象，他们都没有被释放掉。
个人具体探索问题的过程，这里就不赘述了，直接说说我的发现吧。将上文中创建channel的代码：
self.channel = CusFlutterMethodChannel.init(name: "channel", binaryMessenger: self.flutterVC!.binaryMessenger) 复制代码
修改成：
self.channel = CusFlutterMethodChannel.init(name: "channel", binaryMessenger: self.flutterVC!.binaryMessenger, codec: FlutterStandardMethodCodec.sharedInstance()) 复制代码
上述的问题便解决了。从flutter页面返回原生界面时，channel的析构函数触发，控制台日志有输出。
5.疑惑
其实看官方注释的意思，两种构造方法方法区别不大：
/** * Creates a `FlutterMethodChannel` with the specified name and binary messenger. * * The channel name logically identifies the channel; identically named channels * interfere with each other's communication. * * The binary messenger is a facility for sending raw, binary messages to the * Flutter side. This protocol is implemented by `FlutterEngine` and `FlutterViewController`. * * The channel uses `FlutterStandardMethodCodec` to encode and decode method calls * and result envelopes. * * @param name The channel name. * @param messenger The binary messenger. */ + (instancetype)methodChannelWithName:(NSString*)name binaryMessenger:(NSObject<FlutterBinaryMessenger>*)messenger; /** * Creates a `FlutterMethodChannel` with the specified name, binary messenger, and * method codec. * * The channel name logically identifies the channel; identically named channels * interfere with each other's communication. * * The binary messenger is a facility for sending raw, binary messages to the * Flutter side. This protocol is implemented by `FlutterEngine` and `FlutterViewController`. * * @param name The channel name. * @param messenger The binary messenger. * @param codec The method codec. */ + (instancetype)methodChannelWithName:(NSString*)name binaryMessenger:(NSObject<FlutterBinaryMessenger>*)messenger codec:(NSObject<FlutterMethodCodec>*)codec; 复制代码
第一个方法其实就是第二个方法codec默认为FlutterStandardMethodCodec。至于为何第一中方法构造的channel不能释放，只能去看源码才能解惑了。如果大家有好的想法和见解，还请不吝赐教
作者：番茄炒西红柿啊
链接：https://juejin.cn/post/7054436448161759240