Flutter 中的 Intents

可以看看这篇 Flutter 页面跳转，携带参数的页面跳转的使用和说明点击跳转

在Android中，Intent 用来做Activity 之间的跳转，又或者用来发送广播，传递消息。那么，在Flutter中，它有什么替代方式呢？

如果需要在Flutter中进行页面切换，可以使用路由，具体代码如下：

import 'package:flutter/material.dart';//void main() => runApp(MaterialApp(home: DemoApp()));void main() { runApp(MaterialApp( home: DemoApp(), // becomes the route named '/' routes: <String, WidgetBuilder>{ '/a': (BuildContext context) => MyPage(title: "page A"), '/b': (BuildContext context) => MyPage(title: 'page B'), '/c': (BuildContext context) => MyPage(title: 'page C'), }, )); }class MyPage extends StatelessWidget { final String title;MyPage({this.title});Widget build(BuildContext context) { return Center(child: Text(title)); } }class DemoApp extends StatelessWidget { //Widget build(BuildContext context) => Scaffold(body: Signature()); Widget build(BuildContext context) { return Scaffold( body: Center( child: Text("DemoApp"), ), floatingActionButton: FloatingActionButton( onPressed: () => _toPageA(context), tooltip: 'Update Text', child: Icon(Icons.update), ), ); }void _toPageA(BuildContext context) { Navigator.of(context).pushNamed("/a"); } }

首先自定义了 routes 然后定义了按钮点击事件，使其跳转到 pageA 。

routes 定义多个页面并省略 home 的写法

在 Flutter中，编写一个页面，必须提供 home 并 return 一个 Widght 来显示页面，但是在 MaterialApp 中，通过编写 routes 是可以忽略掉 home 的，就像下面的例子：

import 'package:flutter/material.dart';void main() { runApp(new FlutterReduxApp()); }class FlutterReduxApp extends StatelessWidget { FlutterReduxApp({Key key}) : super(key: key);@override Widget build(BuildContext context) { return new MaterialApp(routes: { "/": (context) { //store.state.platformLocale = Localizations.localeOf(context); return MyPage(); }, "/b": (context) { ///通过 Localizations.override 包裹一层， return MyPage(); }, "/c": (context) { return MyPage(); }, }); } }class MyPage extends StatelessWidget { final String title;MyPage({this.title});Widget build(BuildContext context) { return new Scaffold( appBar: new AppBar(title: new Text("this is Push Page")), body: new Center( child: new RaisedButton( child: new Text("点击返回"), onPressed: () => Navigator.of(context).pop("this is result text"), color: Colors.blue, highlightColor: Colors.lightBlue, ), ), ); } }

在routes 中，必须提供 / 这样的一个根目录，否则是会报错的，就像这样

class FlutterReduxApp extends StatelessWidget { FlutterReduxApp({Key key}) : super(key: key);@override Widget build(BuildContext context) { return new MaterialApp(routes: { "/a": (context) { //store.state.platformLocale = Localizations.localeOf(context); return MyPage(); }, "/b": (context) { ///通过 Localizations.override 包裹一层， return MyPage(); }, "/c": (context) { return MyPage(); }, }); } } 

错误：

I/flutter (20735): 'package:flutter/src/widgets/app.dart': Failed assertion: line 178 pos 10: 'builder != null || I/flutter (20735):home != null || I/flutter (20735):routes.containsKey(Navigator.defaultRouteName) || I/flutter (20735):onGenerateRoute != null || I/flutter (20735):onUnknownRoute != null' 

Flutter中如何在dart 和 java 文件之间传递数据？

某些数据需要在java端处理之后，交由界面显示，这时候就需要flutter 和java 之间的交互了

首先，在 java 文件Activity 的onCreate 中定义如下方法：

 package com.example.fluttertestapp;import android.os.Bundle; import android.os.Handler; import android.widget.Toast;import io.flutter.app.FlutterActivity; import io.flutter.plugin.common.MethodCall; import io.flutter.plugin.common.MethodChannel; import io.flutter.plugins.GeneratedPluginRegistrant;public class MainActivity extends FlutterActivity {private final String sharedText = "this is shared text"; Handler handler;@Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); GeneratedPluginRegistrant.registerWith(this); handler = new Handler(); //handler.postDelayed(new Runnable() { //@Override //public void run() { // //Toast.makeText(MainActivity.this, String.format("start main thread:%d", 1600), Toast.LENGTH_SHORT).show(); //} //}, 1600); new MethodChannel(getFlutterView(), "app.channel.shared.data") .setMethodCallHandler(new MethodChannel.MethodCallHandler() { @Override public void onMethodCall(MethodCall methodCall, MethodChannel.Result result) { if (methodCall.method.contentEquals("getSharedText")) { result.success(sharedText); } } });} }

然后在 main.dart 中定义

import 'package:flutter/material.dart'; import 'package:flutter/services.dart';void main() { runApp(SampleApp()); }class SampleApp extends StatelessWidget { // This widget is the root of your application. @override Widget build(BuildContext context) { return MaterialApp( title: 'Sample Shared App Handler', theme: ThemeData( primarySwatch: Colors.blue, ), home: SampleAppPage(), ); } }class SampleAppPage extends StatefulWidget { SampleAppPage({Key key}) : super(key: key);@override _SampleAppPageState createState() => _SampleAppPageState(); }class _SampleAppPageState extends State<SampleAppPage> { static const platform = const MethodChannel('app.channel.shared.data'); String dataShared = "No data";@override void initState() { super.initState(); getSharedText(); }@override Widget build(BuildContext context) { return Scaffold(body: Center(child: Text(dataShared))); }getSharedText() async { var sharedData = await platform.invokeMethod("getSharedText"); if (sharedData != null) { setState(() { dataShared = sharedData; }); } } }

运行程序就可正确的获取到 shareText 了

在看官方demo中，发现了await 字眼，说明应该是延时调用，所以，尝试在 activity 中也延时返回数据，发现，并不会导致程序阻塞，但是会导致数据获取失败，在实际测试中，当延迟在 1600 的时候，有时成功获取 shareText ，有时则失败。具体代码如下：

package com.example.fluttertestapp;import android.os.Bundle; import android.os.Handler; import android.widget.Toast;import io.flutter.app.FlutterActivity; import io.flutter.plugin.common.MethodCall; import io.flutter.plugin.common.MethodChannel; import io.flutter.plugins.GeneratedPluginRegistrant;public class MainActivity extends FlutterActivity {private final String sharedText = "this is shared text"; Handler handler;@Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); GeneratedPluginRegistrant.registerWith(this); handler = new Handler(); handler.postDelayed(new Runnable() { @Override public void run() { new MethodChannel(getFlutterView(), "app.channel.shared.data") .setMethodCallHandler(new MethodChannel.MethodCallHandler() { @Override public void onMethodCall(MethodCall methodCall, MethodChannel.Result result) { if (methodCall.method.contentEquals("getSharedText")) { result.success(sharedText); } } });Toast.makeText(MainActivity.this, String.format("start main thread:%d", 1600), Toast.LENGTH_SHORT).show(); } }, 1600);} }

为了防止调用方法的失败，最好不要在主线程中执行延时线程去返回方法。

Flutter 中如何跳转到另一个页面后，获取返回值？

在Android原生编程中，可以使用 startActivityForResult 来获取另一个页面的返回值，那么，在Flutter 中呢

import 'package:flutter/material.dart';void main() { runApp(MaterialApp( home: DemoApp(), // becomes the route named '/' routes: <String, WidgetBuilder>{ '/a': (BuildContext context) { debugPrint("select route A"); //Navigator.of(context).pop("this is result text"); return MyPage(title: "page A"); } }, )); }class MyPage extends StatelessWidget { final String title;MyPage({this.title});Widget build(BuildContext context) { return new Scaffold( appBar: new AppBar(title: new Text("this is Push Page")), body: new Center( child: new RaisedButton( child: new Text("点击返回"), onPressed: () => Navigator.of(context).pop("this is result text"), color: Colors.blue, highlightColor: Colors.lightBlue, ), ), ); } }class DemoApp extends StatelessWidget { //Widget build(BuildContext context) => Scaffold(body: Signature()); Widget build(BuildContext context) { return Scaffold( body: Center( child: Text("DemoApp"), ), floatingActionButton: FloatingActionButton( onPressed: () => _toPageA(context), tooltip: 'Update Text', child: Icon(Icons.update), ), ); }Future _toPageA(BuildContext context) { debugPrint("this is debug info"); //Navigator.of(context).pushNamed("/a"); Future result = Navigator.of(context).pushNamed("/a"); result.then((value) { debugPrint(value); }); } }

首先，通过 Navigator.of(context).pushNamed("/a") 跳转到另一个页面，然后使用 Future.then 获取返回，这个返回值是在另一个页面中，通过Navigator.of(context).pop("this is result text") 传递而来。

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