当你在开发flutter应用的时候，有时会需要调用native的api，往往遇到flutter并没有相应的package， 这时候flutter plugin就开始发挥作用了，这篇文章将会讲解开发一个简单flutter plugin的步骤和方法，好了，让我们开始动手吧。

1.在Android Studio 中创建一个Flutter Plugin 项目，如下图

上图中你能看到项目描述中写到，如果需要暴露Andorid或iOS的API给开发者时，选择"Plugin"项目类型。
这个项目我们命名为:flutter_native_log_plugin, 当我们完成创建项目后，有两个文件我们需要看一看， 一个是位于android/src下的FlutterNativeLogPlugin.java， 这段代码是用来和本地设备交互，然后将交互结果返回供flutter前端调用， 如下所示：

package com.cube8.flutter_native_log_plugin;import io.flutter.plugin.common.MethodCall;import io.flutter.plugin.common.MethodChannel;import io.flutter.plugin.common.MethodChannel.MethodCallHandler;import io.flutter.plugin.common.MethodChannel.Result;import io.flutter.plugin.common.PluginRegistry.Registrar;/** FlutterNativeLogPlugin */public class FlutterNativeLogPlugin implements MethodCallHandler { /** Plugin registration. */ public static void registerWith(Registrar registrar) { final MethodChannel channel = new MethodChannel(registrar.messenger(), "flutter_native_log_plugin"); channel.setMethodCallHandler(new FlutterNativeLogPlugin()); } @Override public void onMethodCall(MethodCall call, Result result) { if (call.method.equals("getPlatformVersion")) { result.success("Android " + android.os.Build.VERSION.RELEASE); } else { result.notImplemented(); } }}

另一个 /lib/mian.dart文件，这段代码是主要用来和native代码交互， 如下所示：

import 'dart:async';import 'package:flutter/services.dart';class FlutterNativeLogPlugin { static const MethodChannel _channel = const MethodChannel('flutter_native_log_plugin'); static Future<String> get platformVersion async { final String version = await _channel.invokeMethod('getPlatformVersion'); return version; }}

2.现在我们开始编写我们的Plugin.

在lib/flutter_native_log_plugin.dart 文件中，我们先创建一个新的方法，代码如下：

import 'dart:async';import 'package:flutter/material.dart';import 'package:flutter/services.dart';enum Log { DEBUG, WARNING, ERROR }class FlutterNativeLogPlugin { static const MethodChannel _channel = const MethodChannel('flutter_native_log_plugin'); static Future<String> printLog( {Log logType, @required String tag, @required String msg}) async { String log = "debug"; if (logType == Log.WARNING) { log = "warning"; } else if (logType == Log.ERROR) { log = "error"; } else { log = "debug"; } final Map<String, dynamic> params = <String, dynamic>{ 'tag': tag, 'msg': msg, 'logType': log }; final String result = await _channel.invokeMethod('printLog', params); return result; }}

在Android端，我们将android/src下的FlutterNativePlugin.java改写如下：

package com.cube8.flutter_native_log_plugin;import android.util.Log;import io.flutter.plugin.common.MethodCall;import io.flutter.plugin.common.MethodChannel;import io.flutter.plugin.common.MethodChannel.MethodCallHandler;import io.flutter.plugin.common.MethodChannel.Result;import io.flutter.plugin.common.PluginRegistry.Registrar;/** * FlutterNativeLogPlugin */public class FlutterNativeLogPlugin implements MethodCallHandler { /** * Plugin registration. */ public static void registerWith(Registrar registrar) { final MethodChannel channel = new MethodChannel(registrar.messenger(), "flutter_native_log_plugin"); channel.setMethodCallHandler(new FlutterNativeLogPlugin()); } @Override public void onMethodCall(MethodCall call, Result result) { if (call.method.equals("printLog")) { String msg = call.argument("msg"); String tag = call.argument("tag"); String logType = call.argument("logType"); if (logType.equals("warning")) { Log.w(tag, msg); } else if (logType.equals("error")) { Log.e(tag, msg); } else { Log.d(tag, msg); } result.success("Logged Successfully!"); } else { result.notImplemented(); } }}

3.测试plugin。当开发完了我们的plugin之后，我们需要测试这个新plugin是否可用，于是对example/lib的main.dart文件作如下修改：

import 'package:flutter/material.dart';import 'package:flutter_native_log_plugin/flutter_native_log_plugin.dart';void main() => runApp(MyApp());class MyApp extends StatefulWidget { @override _MyAppState createState() => _MyAppState();}class _MyAppState extends State<MyApp> { @override void initState() { super.initState(); } void printLogs() async { print(await FlutterNativeLogPlugin.printLog( tag: "Debug", msg: "This is ordinary Log")); // default logType print(await FlutterNativeLogPlugin.printLog( tag: "Debug", msg: "This is warning Log", logType: Log.WARNING)); // logType = warning print(await FlutterNativeLogPlugin.printLog( tag: "Debug", msg: "This is error Log", logType: Log.ERROR)); // logType = error print(await FlutterNativeLogPlugin.printLog( tag: "Debug", msg: "This is debug Log", logType: Log.DEBUG)); // logType = debug } @override Widget build(BuildContext context) { return MaterialApp( home: Scaffold( appBar: AppBar( title: const Text('Plugin example app'), ), body: Center( child: RaisedButton( child: Text("PrintLogs"), onPressed: printLogs, ), ), ), ); }}

点击app中的按钮，控制台将看到如下输出，说明plugin可以顺利运行了。

4.最后一步就是将我们开发的plugin发布到dart pub供以后直接调用。打开控制台，需要确认定位到plugin项目的根目录，然后输入如下命令：

flutter packages pub publish --dry-run

这段命令会做一个程序相关文件和信息的检查，确保待发布的plugin信息完整，根据控制台的提示完善信息后，与下图相似：

接着输入如下命令，正式将plugin发布到dart pub中：

flutter packages pub publish

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持。