如何使用 Pigeon 包从 Flutter 调用原生 iOS 函数？

Question

我正在尝试在我的项目中集成一些本机代码。为此，我正在使用新的 Pigeon 包：https://pub.dev/packages/pigeon

在 Android 上它工作得很好，但在 iOS 上，每当我尝试调用用 swift 编写的方法时（按下按钮时），它都会抛出 PlatformException(channel-error, Unable to build connection on channel., null, null)

我已经设置了颤振启动项目，然后在按下 floatingActionButton 时调用本机方法。执行本机方法时，它会返回一个字符串，在 android 端显示“Hello from Android”，在 iOS 端返回“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)
  }
}

onPressed 在 Android 上的结果：

在 iOS 上 onPressed 的结果：

另外值得注意的是，当我在 didChangedDependencies 函数中调用 onPressed 中的代码时，swift 中的代码确实运行了，结果确实显示出来了，但随后又抛出了相同的异常。这意味着频道确实被创建了，我只是用错了。

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 swift 的结果，然后抛出同样的错误。

Answer 1

我认为BinaryMessenger 设置不正确。

我试过了，它奏效了： 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)

完整的方法变成这样：

  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)
  }