用Flutter开发自定义Plugin的方法示例

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。