Flutter开发之Widget布局和页面导航

一、水平布局Row

Row控件可以分为非灵活排列和灵活排列两种,灵活的可以在外边加入Expanded使用<br />

两者混用：

import ‘package:flutter/material.dart‘;
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    // TODO: implement build
    return MaterialApp(
      title: ‘‘,
      home: new Scaffold(
        appBar: new AppBar(title: new Text(‘hello row‘)),
        body: new Row(
          children: <Widget>[
            Expanded(                      //灵活使用
                child: new RaisedButton(
                  onPressed: () {},
                  color: Colors.blue,
                  child: new Text(‘Blue Button‘),
                )),
            new RaisedButton(
              onPressed: () {},
              color: Colors.green,
              child: new Text(‘Green Button‘),
            ),
          ],
        ),
      ),
    );
  }
}

二、垂直布局Column

      对齐方式：

• main轴： 比如Row组件，那水平就是主轴。比如Column组件，那垂直就是主轴。

• cross轴：比如Row组件，那垂直就是副轴。比如Columu组件，那水平就是副轴。

import ‘package:flutter/material.dart‘;
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    // TODO: implement build
    return MaterialApp(
      title: ‘‘,
      home: new Scaffold(
        appBar: new AppBar(title: new Text(‘hello Column‘)),
        body: new Center(
          child: new Column(
            crossAxisAlignment: CrossAxisAlignment.center, //副轴对齐方式
            mainAxisAlignment: MainAxisAlignment.center, //主轴对齐方式
            children: <Widget>[
              new Text(‘君不见黄河之水天上来，‘,
                  style: TextStyle(
                    color: Colors.black,
                    fontSize: 30.0,
                  )),
              new Text(‘东流到海不复还，‘,
                  style: TextStyle(
                    color: Colors.redAccent,
                    fontSize: 30.0,
                  )),
            ],
          ),
        ),
      ),
    );
  }
}

三、层叠布局Stack

alignment属性：控制层叠的位置

alignment: const FractionalOffset(dx,dy) dx、dy 为0~1

import ‘package:flutter/material.dart‘;
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    var stack = new Stack(
      alignment: const FractionalOffset(0.5, 0.8),
      children: <Widget>[
        new CircleAvatar(
          backgroundImage:
              new NetworkImage(‘https://profile.csdnimg.cn/0/5/2/1_jyd0124‘),
          radius: 100.0,
        ),
        new Container(
          decoration: BoxDecoration(
            color: Colors.cyan,
          ),
          child: new Text(‘blog_jyd0124‘),
          padding: EdgeInsets.all(5.0),
        ),
      ],
    );
    // TODO: implement build
    return MaterialApp(
      title: ‘‘,
      home: new Scaffold(
        appBar: new AppBar(title: new Text(‘hello Stack‘)),
        body: new Center(child: stack),
      ),
    );
  }
}

说明：CircleAvatar组件经常用来作头像，radius属性可以设置图片的弧度

Stack布局高级用法：Positioned(层叠定位组件)用于层叠多个组件

var stack = new Stack(
      //alignment: const FractionalOffset(0.5, 0.8),
      children: <Widget>[
        new CircleAvatar(
          backgroundImage:
              new NetworkImage(‘https://profile.csdnimg.cn/0/5/2/1_jyd0124‘),
          radius: 100.0,
        ),
        new Positioned(
            bottom: 20.0,
            left: 60.0,
            child: new Container(
              decoration: BoxDecoration(
                color: Colors.cyan,
              ),
              child: new Text(‘blog_jyd0124‘),
              padding: EdgeInsets.all(5.0),
            )),
      ],
    );

四、卡片布局Card

import ‘package:flutter/material.dart‘;
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    var card = new Card(
      child: new Column(
        children: <Widget>[
          ListTile(
            title: new Text(‘成都市‘,style:TextStyle(fontWeight:FontWeight.w100)),
            subtitle: new Text(‘QQ：150048****‘),
            leading: new Icon(Icons.account_balance,color: Colors.blue,),
          ),
          ListTile(
            title: new Text(‘西安市‘,style:TextStyle(fontWeight:FontWeight.w100)),
            subtitle: new Text(‘QQ：150048****‘),
            leading: new Icon(Icons.account_balance,color: Colors.blue,),
          ),
          ListTile(
            title: new Text(‘兰州市‘,style:TextStyle(fontWeight:FontWeight.w100)),
            subtitle: new Text(‘QQ：150048****‘),
            leading: new Icon(Icons.account_balance,color: Colors.blue,),
          ),
        ],
      )
    );
    // TODO: implement build
    return MaterialApp(
      title: ‘‘,
      home: new Scaffold(
        appBar: new AppBar(title: new Text(‘hello Column‘)),
        body: new Center(child: card),
      ),
    );
  }
}

 五、页面的导航和返回

       1.RaisedButton按钮组件

          两个常用属性：

• child：可以放入容器，图标，文字
• onPressed：事件的响应，一般调用Navigator组件

       2.Navigator组件

• Navigator.push()   =====跳转到下一个页面，接受两个参数一个是上下文context，另一个是要跳转的函数。
• Navigator.pop()     =====返回到上一个页面，接受一个context（上下文）参数

import ‘package:flutter/material.dart‘;

void main() => runApp(MaterialApp(
      title: ‘导航演示‘,
      home: new FirstScreen(),
    ));

class FirstScreen extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    // TODO: implement build
    return Scaffold(
      appBar: AppBar(
        title: Text(‘‘),
      ),
      body: Center(
        child: RaisedButton(
            child: Text(‘跳转‘),
            onPressed: () {
              Navigator.push(
                  context,
                  MaterialPageRoute(
                    builder: (context) => new SecondScreen(),
                  ));
            }),
      ),
    );
  }
}

class SecondScreen extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    // TODO: implement build
    return Scaffold(
      body: new Scaffold(
        appBar: new AppBar(title: new Text(‘跳转完成‘)),
        body: new Center(
            child: RaisedButton(
          child: Text(‘返回‘),
          onPressed: () {
            Navigator.pop(context);
          },
        )),
      ),
    );
  }
}

 六、导航参数的传递和接收

import ‘package:flutter/material.dart‘;

class Product {
  String title;
  String description;
  Product(this.title, this.description);
}

void main() {
  runApp(MaterialApp(
    title: ‘导航的数据传递和接受‘,
    home: ProductList(
        products:
            List.generate(20, (i) => Product(‘商品 $i‘, ‘这是一个商品详情，编号为 $i‘))),
  ));
}

class ProductList extends StatelessWidget {
  final List<Product> products;
  ProductList({Key key, @required this.products}) : super(key: key);
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(‘商品列表‘),
      ),
      body: ListView.builder(
          itemCount: products.length,
          itemBuilder: (context, index) {
            return ListTile(
              title: Text(products[index].title),
              onTap: () {
                Navigator.push(
                    context,
                    MaterialPageRoute(
                        builder: (context) =>
                            ProductDetail(product: products[index])));
              },
            );
          }),
    );
  }
}

class ProductDetail extends StatelessWidget {
  final Product product;
  ProductDetail({Key key, @required this.product}) : super(key: key);
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text(‘${product.title}‘)),
      body: Center(
        child: Text(‘${product.description}‘),
      ),
    );
  }
}

• 小技巧 ：Android Studio 中输入stless可以自动生成StatelessWidget，但在VSCode中，需先安装Awesome Flutter snippets插件，然后输入stlss;

七、页面跳转并返回数据

  1.异步请求与等待

           使用async...await

  2.SnackBar

           显示提示信息的一个控件，会自动隐藏，SnackBar是以Scaffold的showSnackBar()方法来进行显示的;

  3.返回数据

           Navigator.pop()带第二个参数就可以

import ‘package:flutter/material.dart‘;

void main() {
  runApp(MaterialApp(
    title: ‘页面跳转返回数据‘,
    home: FirstPage(),
  ));
}

class FirstPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text(‘得到一个数字‘)),
      body: Center(
        child: RouteButton(),
      ),
    );
  }
}

class RouteButton extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return RaisedButton(
      onPressed: () {
        navigateToNumber(context);
      },
      child: Text(‘Get‘),
    );
  }

  navigateToNumber(BuildContext context) async {
    //async是启用异步方法
    final result = await Navigator.push(
        //等待
        context,
        MaterialPageRoute(builder: (context) => Number()));
    Scaffold.of(context).showSnackBar(SnackBar(content: Text(‘$result‘)));
  }
}

class Number extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text(‘我是你找的数‘)),
      body: Center(
        child: Column(
          children: <Widget>[
            RaisedButton(
              child: Text(‘两位数‘),
              onPressed: () {
                Navigator.pop(context, ‘两位数:98‘);
              },
            ),
            RaisedButton(
              child: Text(‘三位数‘),
              onPressed: () {
                Navigator.pop(context, ‘三位数:124‘);
              },
            ),
          ],
        ),
      ),
    );
  }
}

 八、静态资源和项目图片的处理

    在pubspec.yaml文件中声明资源文件

    测试：

import ‘package:flutter/material.dart‘;

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Container(
      child: Image.asset(‘images/csdn.jpg‘),
    );
  }
}

  九、客户端打包(Android)

 1. 配置APP的图片的目录    /android/app/src/main/res/

 2.配置APP的名称、图标和系统权限的目录    /android/app/src/main/AndroidManifest.xml

 3.生成keystore

       <1> flutter doctor -v  命令找到keytool.exe的位置

        <2>cd进入这个目录，然后执行下面命令就会在D盘下面有一个jks的文件

keytool -genkey -v -keystore D:\key.jks -keyalg RSA -keysize 2048 -validity 10000 -alias key

          <3>到项目目录下的android文件夹下，创建一个名为key.properties的文件，并打开粘贴下面的代码

storePassword=<password from previous step>    //输入上一步创建KEY时输入的 密钥库 密码
keyPassword=<password from previous step>    //输入上一步创建KEY时输入的 密钥 密码
keyAlias=key
storeFile=<E:/key.jks>    //key.jks的存放路径

4.配置key注册

     <1>进入项目目录的/android/app/build.gradle文件，在android{这一行前面,加入如下代码

def keystorePropertiesFile = rootProject.file("key.properties")
def keystoreProperties = new Properties()
keystoreProperties.load(new FileInputStream(keystorePropertiesFile))

    <2>把如下代码进行替换

 替换成的代码：

signingConfigs {
    release {
        keyAlias keystoreProperties[‘keyAlias‘]
        keyPassword keystoreProperties[‘keyPassword‘]
        storeFile file(keystoreProperties[‘storeFile‘])
        storePassword keystoreProperties[‘storePassword‘]
    }
}
buildTypes {
    release {
        signingConfig signingConfigs.release
    }
}

 5.生成apk

   在终端输入 flutter build apk，这时候打包成功，可在build\app\outputs\apk\release\找到

   然后在终端输入flutter install 直接安装到