本地访问-MethodChannel
- 本地访问是指跨平台的解决方案，有访问本地android或者ios资源的能力,主要是MethodChannel和MessageChannel两种，第一种是调用方法，第二种是传递信息。通信的双方是Flutter和本地操作系统或者应用，而且方法的调用和消息的方法可以从任何一方发起，类似远程过程调用。
- Flutter是一个比较独立的环境，要想访问本地的资源，Flutter提供了Channel机制，类似Cilent-Server模式或者RPC
- 通过Channel的名称打通Channel，隧道
- Flutter和本地是对称的，请求可以从任何一发发起，这篇文章主要是记录从Flutter给本地发送请求
- 首先我们创建Flutte工程,ide随你自己喜欢，修改UI代码如下:
import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
import 'dart:async';
void main() => runApp(new MyApp());
class MyApp extends StatelessWidget {
// This widget is the root of your application.
@override
Widget build(BuildContext context) {
return new MaterialApp(
title: 'Flutter Demo',
theme: new ThemeData(
primarySwatch: Colors.blue,
),
home: new MyHomePage(title: 'Flutter Demo Home Page'),
);
}
}
class MyHomePage extends StatefulWidget {
final String title;
@override
_MyHomePageState createState() => new _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
int _counter = 0;
static const platformMethodChannel = const MethodChannel("com.xyjy.flutterchannel/test");
num nativeMessage = 0;
void _incrementCounter() {
setState(() {
_counter++;
});
}
Future<Null> getData() async{
num _message;
try{
final num result = await platformMethodChannel.invokeMethod("getTime");
_message = result;
}
on PlatformException catch(e){
print(e.message);
}
setState(() {
nativeMessage = _message;
});
}
@override
Widget build(BuildContext context) {
return new Scaffold(
appBar: new AppBar(
// Here we take the value from the MyHomePage object that was created by
// the App.build method, and use it to set our appbar title.
title: new Text(widget.title),
),
body: new Center(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
new Text(
"$nativeMessage",
),
new Text(
'$nativeMessage',
style: Theme.of(context).textTheme.display1,
),
],
),
),
floatingActionButton: new FloatingActionButton(
onPressed: ()=>getData(),
tooltip: 'Increment',
child: new Icon(Icons.add),
), // This trailing comma makes auto-formatting nicer for build methods.
);
}
}
- 很简单我只是将_counter显示的替换成了自己定义的nativeMessage，接着往下
- 首先我们要引入service包和async包。
import 'package:flutter/services.dart';
import 'dart:async';
- 声明一个static const变量platformMethodChannel ，赋值MethodChannel类型的对象。
class _MyHomePageState extends State<MyHomePage> {
int _counter = 0;
static const platformMethodChannel = const MethodChannel("com.xyjy.flutterchannel/test");
num nativeMessage = 0;
void _incrementCounter() {
setState(() {
_counter++;
});
}
- 在上面我们要注意，给MethodChannel一个名字com.xyjy.flutterchannel/test,这个名字和本地（这里代表android部分）那边的要一样
我们创建了MethodChannel，我们准备一个用来发送请求的函数。我们创建一个叫getData的异步函数
await platformMethodChannel.invokeMethod('getTime') 是调用本地的getTime方法，并且这个方法是异步的，await表示阻塞执行。
nativeMessage = _message; 表示通知Flutter状态改变，刷新界面。
Future<Null> getData() async{
// num是数字类型
num _message;
try{
final num result = await platformMethodChannel.invokeMethod("getTime");
_message = result;
}
on PlatformException catch(e){
print(e.message);
}
setState(() {
nativeMessage = _message;
});
}
- 修改build里面的显示，将_counter 替换为nativeMessage ，并将floatingActionButton的onTap事件替换为我们定义好的getData方法
@override
Widget build(BuildContext context) {
return new Scaffold(
appBar: new AppBar(
// Here we take the value from the MyHomePage object that was created by
// the App.build method, and use it to set our appbar title.
title: new Text(widget.title),
),
body: new Center(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
new Text(
"$nativeMessage",
),
new Text(
'$nativeMessage',
style: Theme.of(context).textTheme.display1,
),
],
),
),
floatingActionButton: new FloatingActionButton(
onPressed: ()=>getData(),
tooltip: 'Increment',
child: new Icon(Icons.add),
), // This trailing comma makes auto-formatting nicer for build methods.
);
}
- 接下来本地方法如何编写，打开MainActivity
public class MainActivity extends FlutterActivity {
private static final String CHANNAL = "com.xyjy.flutterchannel/test";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
GeneratedPluginRegistrant.registerWith(this);
new MethodChannel(getFlutterView() , CHANNAL).setMethodCallHandler(new MethodChannel.MethodCallHandler()
{
@Override
public void onMethodCall(MethodCall methodCall, MethodChannel.Result result)
{
if (methodCall.method.equals("getTime"))
{
long time = getTime();
result.success(time);
}
else
{
result.notImplemented();
}
}
});
}
private long getTime()
{
return System.currentTimeMillis();
}
}
-
CHANNAL 里面的字符串一定是与Flutter定义一致，在MethodChannel的中调用.setMethodCallHandler() 方法，需要一个MethodCallHandler 对象，是一个匿名内部类，有一个方法onMethodCall,在Flutter发送请求时，onMethodCall方法会执行， result.success(time);返回信息,这样就可以进行本地调用，点击悬浮按钮得到时间(此时的时间是通过本地返回的时间)
QQ图片20180709174145.png
