在前一篇文章中，我们在 Flutter 端让 Android 端发出了 Toast，但内容是在 Android 端定义的，如何从 Flutter 端传递参数到 Android 呢？

Flutter to Android

在 Flutter 端 MethodChannel 的 invokeMethod 方法还有第二个参数：

  @optionalTypeArgs
  Future<T> invokeMethod<T>(String method, [ dynamic arguments ]) {
    return _invokeMethod<T>(method, missingOk: false, arguments: arguments);
  }

它接收一个 Map，我们要传递到 Android 端的数据以键值对的形式进行传递，例如：

    String result =  await _channel.invokeMethod('showToast', {
      "content": message,
      "number": 1233,
    });

Android to Flutter

在 Android 端向 Flutter 发送数据也十分简单，直接调用 Result 对象的 success 方法即可：

result.success("已经发送成功");

可以传递的数据结构

在 Flutter 和 Android/iOS 之间并不是所有数据类型都可以传递的，只有以下可以

示例

android_toast_plugin.dart

import 'dart:async';

import 'package:flutter/services.dart';

class AndroidToastPlugin {
  static const MethodChannel _channel =
      const MethodChannel('ANDROID_TOAST_PLUGIN');

  static Future<String> showToast(String message) async {
    String result =  await _channel.invokeMethod('showToast', {
      "content": message,
      "number": 1233,
    });
    return result;
  }
}

AndroidToastPlugin.java

public class AndroidToastPlugin implements FlutterPlugin, MethodCallHandler {
    private MethodChannel channel;

    @Override
    public void onAttachedToEngine(@NonNull FlutterPluginBinding flutterPluginBinding) {
        channel = new MethodChannel(flutterPluginBinding.getFlutterEngine().getDartExecutor(), "ANDROID_TOAST_PLUGIN");
        channel.setMethodCallHandler(this);
        context = flutterPluginBinding.getApplicationContext();
    }

    static FlutterView view;

    static Context context;

    public static void registerWith(Registrar registrar) {
        final MethodChannel channel = new MethodChannel(registrar.messenger(), "ANDROID_TOAST_PLUGIN");
        channel.setMethodCallHandler(new AndroidToastPlugin());
        context = registrar.context();
    }

    @Override
    public void onMethodCall(@NonNull MethodCall call, @NonNull Result result) {
        if (call.method.equals("showToast")) {
            String message = call.argument("content");
            int number = call.argument("number");
            Toast.makeText(context,message + number,Toast.LENGTH_SHORT).show();
            result.success("已经发送成功");
        } else {
            result.notImplemented();
        }
    }

    @Override
    public void onDetachedFromEngine(@NonNull FlutterPluginBinding binding) {
        channel.setMethodCallHandler(null);
    }
}

使用插件代码，main.dart

import 'package:flutter/material.dart';
import 'package:lixyz/android_taost_plugin.dart';

import 'package:flutter/services.dart';
import 'dart:async';

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

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

class _MyAppState extends State<MyApp> {

  String result = "嘻嘻嘻";

  Future<void> sendToastMessage(String message) async {
    try {
      result = await AndroidToastPlugin.showToast(message);
      print(result);
    } on PlatformException {
      result = 'result is null';
    }
    if (!mounted) return;


  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: const Text('Plugin example app'),
        ),
        body: Column(
          children: <Widget>[
            Text(result),
            Center(
              child: MaterialButton(
                child: Text("点击弹出 Toast"),
                color: Colors.blue,
                onPressed: () {
                  sendToastMessage("这是要显示的内容");
                },
              ),
            ),
          ],
        ),
      ),
    );
  }
}