Flutter基础用法解析

解析开始

Flutter中一切皆widget，一切皆组件。学习Flutter中，必须首先了解Flutter的widget.先从最基本的MaterialApp和Scaffold开始了解

1 MaterialApp

一个封装了很多Android MD设计所必须要的组件的小部件，一般作为顶层widget使用。

继承关系
Inheritance
Object->Diagnosticable ->DiagnosticableTree ->Widget ->StatefulWidget ->MaterialApp

一般与以下widget一起使用
Scaffold: Material Design布局结构的基本实现。此类提供了用于显示drawer、snackbar和底部sheet的API。
Navigator，用于管理应用程序的页面堆栈。
MaterialPageRoute，它定义以特定于材料的方式转换的应用页面。
WidgetsApp，它定义基本的app元素但不依赖于材质库。

一般来说，在Flutter中，我们如果遵循MD设计时，顶层的Widget一般是MaterialApp，这里面我们可以指定主题样式，以便应用与APP整个页面中

2 Scaffold

Material Design布局结构的基本实现。此类提供了用于显示drawer、snackbar和底部sheet的API。
简单来说，Scanold就是一个提供MD设计中基本布局的widget,包括最上面的appBar,body，以及下部的drawer,snackbar等

import 'package:flutter/material.dart';
void main() {
  runApp(new MaterialApp(
    title: 'My app', // used by the OS task switcher
    home: new MyScaffold(),
  ));
}

class MyScaffold extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    // Material 是UI呈现的“一张纸”
    return new Material(
      // Column is 垂直方向的线性布局.
      child: new Column(
        children: <Widget>[
          new MyAppBar(
            title: new Text(
              'Example title',
              style: Theme.of(context).primaryTextTheme.title,
            ),
          ),
          new Expanded(
            child: new Center(
              child: new Text('Hello, world!'),
            ),
          ),
        ],
      ),
    );
  }
}

class MyAppBar extends StatelessWidget {
  MyAppBar({this.title});
  // Widget子类中的字段往往都会定义为"final"
  final Widget title;
  @override
  Widget build(BuildContext context) {
    return new Container(
      height: 56.0, // 单位是逻辑上的像素（并非真实的像素，类似于浏览器中的像素）
      padding: const EdgeInsets.symmetric(horizontal: 8.0),
      decoration: new BoxDecoration(color: Colors.blue[500]),
      // Row 是水平方向的线性布局（linear layout）
      child: new Row(
        //列表项的类型是 <Widget>
        children: <Widget>[
          new IconButton(
            icon: new Icon(Icons.menu),
            tooltip: 'Navigation menu',
            onPressed: null, // null 会禁用 button
          ),
          // Expanded expands its child to fill the available space.
          new Expanded(
            child: title,
          ),
          new IconButton(
            icon: new Icon(Icons.search),
            tooltip: 'Search',
            onPressed: null,
          ),
        ],
      ),
    );
  }
}

import 'package:flutter/material.dart';

void main() {
  runApp(new MaterialApp(
    title: 'Flutter Tutorial',
    home: new TutorialHome(),
  ));
}

class TutorialHome extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    //Scaffold是Material中主要的布局组件.
    return new Scaffold(
      appBar: new AppBar(
        leading: new IconButton(
          icon: new Icon(Icons.menu),
          tooltip: 'Navigation menu',
          onPressed: null,
        ),
        title: new Text('Example title'),
        actions: <Widget>[
          new IconButton(
            icon: new Icon(Icons.search),
            tooltip: 'Search',
            onPressed: null,
          ),
        ],
      ),
      //body占屏幕的大部分
      body: new Center(
        child: new Text('Hello, world!'),
      ),
      floatingActionButton: new FloatingActionButton(
        tooltip: 'Add', // used by assistive technologies
        child: new Icon(Icons.add),
        onPressed: null,
      ),
    );
  }
}

import 'package:flutter/material.dart';

void main() {
  runApp(new MaterialApp(
    title: 'Flutter Tutorial',
    home: new TutorialHome(),
  ));
}

class TutorialHome extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(
        title: new Text('应用'),
      ),
      body: new Center(
        child: new Text('Hello'),
      ),
    );
  }
}

import 'package:flutter/material.dart';

void main() {
  runApp(new MaterialApp(
    title: 'Flutter Tutorial',
    home: new MyApp(),
  ));
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {

    return new MaterialApp(
      title: 'Flutter base UI Widget',
      home: new Scaffold(
        appBar: new AppBar(
          title: new Text('Flutter base UI Widget'),
        ),
        body: new ListView(
          children: <Widget>[
            //add code
            new Text('Hello World', style: new TextStyle(fontSize: 32.0)),
            new Image.asset('images/lake.jpeg',  200.0,height: 200.0, fit: BoxFit.cover),
            new Icon(Icons.star, color: Colors.red[500])
          ],
        ),
      ),
    );
  }
}

import 'package:flutter/material.dart';

void main() {
  runApp(new MaterialApp(
    title: 'Flutter Tutorial',
    home: new MyApp(),
  ));
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    Widget titleSection = new Container(
      padding: const EdgeInsets.all(32.0),
      child: new Row(
        children: [
          new Expanded(
            child: new Column(
              crossAxisAlignment: CrossAxisAlignment.start,
              children: [
                new Container(
                  padding: const EdgeInsets.only(bottom: 8.0),
                  child: new Text(
                    'Oeschinen Lake Campground',
                    style: new TextStyle(
                      fontWeight: FontWeight.bold,
                    ),
                  ),
                ),
                new Text(
                  'Kandersteg, Switzerland',
                  style: new TextStyle(
                    color: Colors.grey[500],
                  ),
                ),
              ],
            ),
          ),
          new Icon(
            Icons.star,
            color: Colors.red[500],
          ),
          new Text('41'),
        ],
      ),
    );

    return new MaterialApp(
      title: 'Flutter base UI Widget',
      home: new Scaffold(
        appBar: new AppBar(
          title: new Text('Flutter base UI Widget'),
        ),
        body: new ListView(
          children: <Widget>[
            //add code
            titleSection
          ],
        ),
      ),
    );
  }
}

import 'package:flutter/material.dart';

void main() {
  runApp(new MaterialApp(
    title: 'Flutter Tutorial',
    home: new MyApp(),
  ));
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'Flutter Demo',
      theme: new ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: new MyHomePage(title: 'GridView Demo'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => new _MyHomePageState();
}

List<Container> _buildGridTileList(int count) {
  List<Container> containers = new List<Container>.generate(
      count,
          (int index) =>
      new Container(child: new Image.asset('images/lake.jpeg', 100.0,height: 100.0, fit: BoxFit.cover)));
  return containers;
}

Widget buildGrid() {
  return new GridView.extent(
      maxCrossAxisExtent: 150.0,
      padding: const EdgeInsets.all(4.0),
      mainAxisSpacing: 4.0,
      crossAxisSpacing: 4.0,
      children: _buildGridTileList(30));
}

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(
        title: new Text(widget.title),
      ),
      body: new Center(
        child: buildGrid(),
      ),
    );
  }
}

import 'package:flutter/rendering.dart' show debugPaintSizeEnabled;
import 'package:flutter/material.dart';

void main() {
//  debugPaintSizeEnabled = true;
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    //关键代码
    var card = new SizedBox(
      height: 210.0,  //设置高度
      child: new Card(
        elevation: 15.0,  //设置阴影
        shape: const RoundedRectangleBorder(borderRadius: BorderRadius.all(Radius.circular(14.0))),  //设置圆角
        child: new Column(  // card只能有一个widget，但这个widget内容可以包含其他的widget
          children: [
            new ListTile(
              title: new Text('标题',
                  style: new TextStyle(fontWeight: FontWeight.w500)),
              subtitle: new Text('子标题'),
              leading: new Icon(
                Icons.restaurant_menu,
                color: Colors.blue[500],
              ),
            ),
            new Divider(),
            new ListTile(
              title: new Text('内容一',
                  style: new TextStyle(fontWeight: FontWeight.w500)),
              leading: new Icon(
                Icons.contact_phone,
                color: Colors.blue[500],
              ),
            ),
            new ListTile(
              title: new Text('内容二'),
              leading: new Icon(
                Icons.contact_mail,
                color: Colors.blue[500],
              ),
            ),
          ],
        ),
      ),
    );
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
        elevation: 5.0, // tabbar的阴影
      ),
      body: Center(
        child: card,
      ),
    );
  }
}