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 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 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 params = {
'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 {
@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如果你喜欢这篇文章或者认为有收获，请给这篇文章点个赞，你的支持就是笔者继续努力写文章的动力。