flutter 学习日记（1）

一 根据codelab https://codelabs.flutter-io.cn/codelabs/first-flutter-app-pt1-cn/index.html#0 制作第一个flutter app
配置好环境后，运行IDE自动生成的flutter demo一直卡在 Running Gradle task 'assembleDebug’或报connect timeout错误，需要在android/build.gradle中修改repository地址。
buildscript 和 allprojects都需要改。

repositories {
		//google()
		//jcenter()
        maven { url 'https://maven.aliyun.com/repository/google' }
        maven { url 'https://maven.aliyun.com/repository/jcenter' }
        maven { url 'https://maven.aliyun.com/repository/public' }
        maven { url 'http://download.flutter.io'}
    }

改完后发现并没有解决问题，这是因为flutter自带的gradle里仍然有地址需要修改
flutter\packages\flutter_tools\gradle\ 中

flutter.gradle
repositories {
		//google()
		//jcenter()
        maven { url 'https://maven.aliyun.com/repository/google' }
        maven { url 'https://maven.aliyun.com/repository/jcenter' }
        maven { url 'https://maven.aliyun.com/repository/public' }
    }
------------------------------------------
private static final String MAVEN_REPO 改为 "download.flutter.io"

resolve_dependencies.gradle
repositories {
    maven {
        url "http://download.flutter.io"
    }
}

再次运行，成功~（还是不行的话也可能是网络不好，可以换流量试试）

codelab的教程还是非常详细的，照着做基本没有什么问题。
成果图

做完后想自己添加一些新功能，比如在喜欢列表的页面里点击项目可以把该项目取消喜欢。

_navigateToSaved() {
    Navigator.of(context)
        .push(new MaterialPageRoute(builder: (BuildContext context) {
      final Iterable<ListTile> tiles = _saved.map(
        (WordPair pair) {
          return new ListTile(
            title: new Text(
              pair.asPascalCase,
              style: _fontSize,
            ),
            trailing: new Icon(
              // 新增代码开始 ...
              Icons.favorite,
              color: Colors.red,
            ),
          );
        },
      );
      _divided = ListTile.divideTiles(context: context, tiles: tiles).toList();
      return savedList(
        saved: _saved,
        divided: _divided,
      );
//        new Scaffold(
//        // 新增 6 行代码开始 ...
//        appBar: new AppBar(
//          title: const Text('Saved Suggestions'),
//        ),
////        body: new ListView(children: divided,)
//        body: ListView.builder(
//            itemCount: divided.length,
//            itemBuilder: (context, index) {
//              if (index < divided.length) {
//                final item = divided[index];
//                return GestureDetector(
//                  onTap: () {
//                divided.removeAt(index);
//                setState(() {});
//                  },
//                  child: item,
//                );
//              }
//            }),
//      );
    }));
  }

一开始想直接在 MaterialPageRoute 的builder里直接返回onTap逻辑，但这样点击后列表中确实删除了，但setState并没有生效，没有重新渲染页面。

后来觉得应该直接再写一个widget，单独控制state

class savedList extends StatefulWidget {
  final saved;
  final divided;
  savedList({this.saved, this.divided});
  @override
  State<StatefulWidget> createState() => _savedListState(saved, divided);
}

class _savedListState extends State<savedList> {
  var saved;
  var divided;
  _savedListState(this.saved, this.divided);
  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar:
          new AppBar(title: const Text('Saved Suggestions'),
          ),
//        body: new ListView(children: divided,)
      body: ListView.builder(
          itemCount: divided.length,
          itemBuilder: (context, index) {
            if (index < divided.length) {
              final item = divided[index];
              return GestureDetector(
                onTap: () {
                  _divided.removeAt(index);
                  _saved.removeAt(index);
                  setState(() {});
                },
                child: item,
              );
            }
          }),
    );
  }
}

这样喜欢列表的页面可以刷新了，但返回后的列表仍然没有刷新，这时需要重写返回按钮

new AppBar(title: const Text('Saved Suggestions'),
              leading:
              new IconButton(
                icon: const Icon(Icons.arrow_back),
                //pop时随便带个参数
                onPressed: () => {Navigator.of(context).pop("aaa")},
              )
          ),

_navigateToSaved方法中,push后加上.then(value)=>{setState(){});
这样就可以接到pop的参数，实现刷新。

完整代码

import 'package:flutter/material.dart';
import 'package:english_words/english_words.dart';

void main() => runApp(MyApp());

var _wordList = <WordPair>[];
var _saved = <WordPair>[];
var _fontSize = TextStyle(fontSize: 18.0);
var _divided = <Widget>[];

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(title: 'Welcome to Flutter', home: RandomWords());
  }
}

class RandomWords extends StatefulWidget {
  @override
  _RandomWordsState createState() => _RandomWordsState();
}

class _RandomWordsState extends State<RandomWords> {
  Widget _buildWordList() {
    return ListView.builder(
        padding: EdgeInsets.all(16),
        itemBuilder: (context, i) {
          if (i.isOdd) {
            return Divider();
          }
          final index = i ~/ 2;
          if (index >= _wordList.length) {
            _wordList.addAll(generateWordPairs().take(10));
          }
          return _buildRow(_wordList[index]);
        });
  }

  Widget _buildRow(WordPair pair) {
    final bool alreadySaved = _saved.contains(pair);
    return ListTile(
      title: Text(
        pair.asPascalCase,
        style: _fontSize,
      ),
      trailing: new Icon(
        // 新增代码开始 ...
        alreadySaved ? Icons.favorite : Icons.favorite_border,
        color: alreadySaved ? Colors.red : null,
      ),
      onTap: () {
        setState(() {
          if (alreadySaved) {
            _saved.remove(pair);
          } else {
            _saved.add(pair);
          }
        });
      },
    );
  }

  _navigateToSaved() {
    Navigator.of(context)
        .push(new MaterialPageRoute(builder: (BuildContext context) {
      final Iterable<ListTile> tiles = _saved.map(
        (WordPair pair) {
          return new ListTile(
            title: new Text(
              pair.asPascalCase,
              style: _fontSize,
            ),
            trailing: new Icon(
              // 新增代码开始 ...
              Icons.favorite,
              color: Colors.red,
            ),
          );
        },
      );
      _divided = ListTile.divideTiles(context: context, tiles: tiles).toList();
      return savedList(
        saved: _saved,
        divided: _divided,
      );
    })).then((value) => setState(() {}));
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Startup Name Generator'),
        actions: <Widget>[
          new IconButton(
              icon: const Icon(Icons.list), onPressed: _navigateToSaved)
        ],
      ),
      body: _buildWordList(),
    );
  }
}

class savedList extends StatefulWidget {
  final saved;
  final divided;
  savedList({this.saved, this.divided});
  @override
  State<StatefulWidget> createState() => _savedListState(saved, divided);
}

class _savedListState extends State<savedList> {
  var saved;
  var divided;
  _savedListState(this.saved, this.divided);
  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      // 新增 6 行代码开始 ...
      appBar:
          new AppBar(title: const Text('Saved Suggestions'),
              leading:
              new IconButton(
                icon: const Icon(Icons.arrow_back),
                onPressed: () => {Navigator.of(context).pop("aaa")},
              )
          ),
      body: ListView.builder(
          itemCount: divided.length,
          itemBuilder: (context, index) {
            if (index < divided.length) {
              final item = divided[index];
              return GestureDetector(
                onTap: () {
                  _divided.removeAt(index);
                  _saved.removeAt(index);
                  setState(() {});
                },
                child: item,
              );
            }
          }),
    );
  }
}