Flutter 中的 Intents

可以看看這篇 Flutter 頁面跳轉，攜帶參數的頁面跳轉的使用和說明點擊跳轉

在Android中，Intent 用來做Activity 之間的跳轉，又或者用來發送廣播，傳遞消息。那么，在Flutter中，它有什么替代方式呢？

如果需要在Flutter中進行頁面切換，可以使用路由，具體代碼如下：

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"); } }

首先自定義了 routes 然后定義了按鈕點擊事件，使其跳轉到 pageA 。

routes 定義多個頁面并省略 home 的寫法

在 Flutter中，編寫一個頁面，必須提供 home 并 return 一個 Widght 來顯示頁面，但是在 MaterialApp 中，通過編寫 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) { ///通過 Localizations.override 包裹一層， 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("點擊返回"), onPressed: () => Navigator.of(context).pop("this is result text"), color: Colors.blue, highlightColor: Colors.lightBlue, ), ), ); } }

在routes 中，必須提供 / 這樣的一個根目錄，否則是會報錯的，就像這樣

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) { ///通過 Localizations.override 包裹一層， return MyPage(); }, "/c": (context) { return MyPage(); }, }); } } 

錯誤：

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 文件之間傳遞數據？

某些數據需要在java端處理之后，交由界面顯示，這時候就需要flutter 和java 之間的交互了

首先，在 java 文件Activity 的onCreate 中定義如下方法：

 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 中定義

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; }); } } }

運行程序就可正確的獲取到 shareText 了

在看官方demo中，發現了await 字眼，說明應該是延時調用，所以，嘗試在 activity 中也延時返回數據，發現，并不會導致程序阻塞，但是會導致數據獲取失敗，在實際測試中，當延遲在 1600 的時候，有時成功獲取 shareText ，有時則失敗。具體代碼如下：

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);} }

為了防止調用方法的失敗，最好不要在主線程中執行延時線程去返回方法。

Flutter 中如何跳轉到另一個頁面后，獲取返回值？

在Android原生編程中，可以使用 startActivityForResult 來獲取另一個頁面的返回值，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("點擊返回"), 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，通過 Navigator.of(context).pushNamed("/a") 跳轉到另一個頁面，然后使用 Future.then 獲取返回，這個返回值是在另一個頁面中，通過Navigator.of(context).pop("this is result text") 傳遞而來。

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