如何使用Pigeon包从Flutter调用原生iOS函数？

Question

我正在尝试将一些本地代码集成到我的项目中。为此，我使用新的Pigeon包：https://pub.dev/packages/pigeon

在安卓上它工作得很好，但是在iOS上，每当我试图调用用swift编写的方法(按下按钮时)时，它抛出一个通道错误(PlatformException-error，Unable to establish connection On channel.，null，null)

我已经设置了flutter启动项目，然后当按下floatingActionButton时，我将调用本机方法。当执行本机方法时，它会在Android端返回一个字符串"Hello from Android“，并在iOS上返回"Hello from Xcode”。

main.dart文件：

import 'package:flutter/material.dart';
import 'package:platforms/pigeon.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key? key, required this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;


  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'You have pushed the button this many times:',
            ),
            Text(
              '$_counter',
              style: Theme.of(context).textTheme.headline4,
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () async {
          Api api = Api();
          final searchReply = await api.search(SearchRequest());
          print(searchReply.result);
        },
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ),
    );
  }
}

MainActivity.java文件：

package com.example.platforms;
import android.os.Bundle;
import io.flutter.embedding.android.FlutterActivity;

public class MainActivity extends FlutterActivity {
    private class Api implements Pigeon.Api {

        @Override
        public Pigeon.SearchReply search(Pigeon.SearchRequest arg) {
            Pigeon.SearchReply searchReply = new Pigeon.SearchReply();
            searchReply.setResult("Hello from Android!");
            return searchReply;
        }
    }

    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        Pigeon.Api.setup(getFlutterEngine().getDartExecutor().getBinaryMessenger(), new Api());
    }
    
}

AppDelegate.swift文件：

import UIKit
import Flutter




@UIApplicationMain
@objc class AppDelegate: FlutterAppDelegate, Api {
    var engine: FlutterEngine = {
        let result = FlutterEngine.init()
        // This could be `run` earlier in the app to avoid the overhead of doing it the first time the
        // engine is needed.
        result.run()
        return result
      }()
    
    
    func search(_ input: SearchRequest, error: AutoreleasingUnsafeMutablePointer<FlutterError?>) -> SearchReply? {
        
        let reply = SearchReply()
        
        reply.result = "Hello from Xcode!!!!"
        return reply
    }
    
    
  override func application(
    _ application: UIApplication,
    didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?
  ) -> Bool {
    
    GeneratedPluginRegistrant.register(with: self)
    ApiSetup(engine.binaryMessenger, self)
    return super.application(application, didFinishLaunchingWithOptions: launchOptions)
  }
}

在安卓系统上运行onPressed的结果：

​

在iOS上执行onPressed的结果：

​

同样值得注意的是，当我在didChangedDependencies函数中调用onPressed中的代码时，swift中的代码确实会运行，结果也会显示出来，但随后会再次抛出相同的异常。这意味着通道确实被创建了，我只是错误地使用了它。

当它被添加到main.dart时

@override
  void didChangeDependencies() async {
    Api api = Api();
    final searchReply = await api.search(SearchRequest());
    print(searchReply.result);
    super.didChangeDependencies();
  }

​

​

它打印来自swift的结果，然后抛出相同的错误。

Answer 1

我认为BinaryMessenger设置得不正确。

我尝试过这样做，它起作用了:在didFinishLaunchingWithOptions方法中，获取rootViewController并将其转换为FlutterBinaryMessenger

let rootViewController : FlutterViewController = window?.rootViewController as! FlutterViewController
// get binaryMessenger
let binaryMessenger = rootViewController as! FlutterBinaryMessenger
    
// set binaryMessenger
ApiSetup(binaryMessenger, self)

完整的方法如下所示：

  override func application(
    _ application: UIApplication,
    didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?
  ) -> Bool {
    GeneratedPluginRegistrant.register(with: self);
    
    let rootViewController : FlutterViewController = window?.rootViewController as! FlutterViewController
    
    // get binaryMessenger
    let binaryMessenger = rootViewController as! FlutterBinaryMessenger
    
    // set binaryMessenger
    ApiSetup(binaryMessenger, self)

    return super.application(application, didFinishLaunchingWithOptions: launchOptions)
  }