Flutter基础布局

Column:纵向布局

Column相当于Android原生的LinearLayout线性布局。

主要代码：

class MyHomePage extends StatelessWidget {
  const MyHomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Container(
      width: double.infinity,
      height: double.infinity,
      color: Colors.white,
      child: const Column(
        //start:主轴容器内起始位排列
        //end:主轴容器内结束位排列
        //center:主轴容器内居中排列
        //spaceBetween:主轴容器内均匀排列（顶部底部无间距，间距相等）
        //spaceAround:主轴容器内相同间隔分布（顶部底部间距相等，控件之间间距相等）
        //spaceEvenly:主轴容器内等距离分布（顶部底部同等间距，间距相等）
        mainAxisAlignment: MainAxisAlignment.center,
        //start:横轴容器内起始位排列
        //end:横轴容器内结束位排列
        //center:横轴容器内居中排列
        //stretch:横轴容器内拉伸排列
        crossAxisAlignment: CrossAxisAlignment.center,
        children: [
          IconContainer(Icons.home),
          IconContainer(Icons.search, color: Colors.yellow),
          IconContainer(Icons.ac_unit, color: Colors.orange)
        ],
      ),
    );
  }
}

mainAxisAlignment和crossAxisAlignment属性用于控制排列位置与控件之间距离。

完整代码：

import 'package:flutter/material.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData(primarySwatch: Colors.blue),
      home: Scaffold(
        appBar: AppBar(
          title: const Text("Flutter"),
        ),
        body: const MyHomePage(),
      ),
    );
  }
}

class MyHomePage extends StatelessWidget {
  const MyHomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Container(
      width: double.infinity,
      height: double.infinity,
      color: Colors.white,
      child: const Column(
        //start:主轴容器内起始位排列
        //end:主轴容器内结束位排列
        //center:主轴容器内居中排列
        //spaceBetween:主轴容器内均匀排列（顶部底部无间距，间距相等）
        //spaceAround:主轴容器内相同间隔分布（顶部底部间距相等，控件之间间距相等）
        //spaceEvenly:主轴容器内等距离分布（顶部底部同等间距，间距相等）
        mainAxisAlignment: MainAxisAlignment.center,
        //start:横轴容器内起始位排列
        //end:横轴容器内结束位排列
        //center:横轴容器内居中排列
        //stretch:横轴容器内拉伸排列
        crossAxisAlignment: CrossAxisAlignment.center,
        children: [
          IconContainer(Icons.home),
          IconContainer(Icons.search, color: Colors.yellow),
          IconContainer(Icons.ac_unit, color: Colors.orange)
        ],
      ),
    );
  }
}

class IconContainer extends StatelessWidget {
  final Color color;
  final IconData icon;

  const IconContainer(this.icon, {Key? key, this.color = Colors.red})
      : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Container(
      alignment: Alignment.center,
      width: 100,
      height: 100,
      color: color,
      child: Icon(icon, color: Colors.white, size: 28),
    );
  }
}

Row:横向布局

主要代码：

class MyHomePage extends StatelessWidget {
  const MyHomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Container(
      width: double.infinity,
      height: double.infinity,
      color: Colors.white,
      child: const Row(
        mainAxisAlignment: MainAxisAlignment.center,
        crossAxisAlignment: CrossAxisAlignment.center,
        children: [
          IconContainer(Icons.home),
          IconContainer(Icons.search, color: Colors.yellow),
          IconContainer(Icons.ac_unit, color: Colors.orange)
        ],
      ),
    );
  }
}

Row和Column相对应，Row横向依次排列容器内的内容，Column纵向依次排列容器内的内容。属性介绍参考Column。

完整代码：

import 'package:flutter/material.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData(primarySwatch: Colors.blue),
      home: Scaffold(
        appBar: AppBar(
          title: const Text("Flutter"),
        ),
        body: const MyHomePage(),
      ),
    );
  }
}

class MyHomePage extends StatelessWidget {
  const MyHomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Container(
      width: double.infinity,
      height: double.infinity,
      color: Colors.white,
      child: const Row(
        mainAxisAlignment: MainAxisAlignment.center,
        crossAxisAlignment: CrossAxisAlignment.center,
        children: [
          IconContainer(Icons.home),
          IconContainer(Icons.search, color: Colors.yellow),
          IconContainer(Icons.ac_unit, color: Colors.orange)
        ],
      ),
    );
  }
}

class IconContainer extends StatelessWidget {
  final Color color;
  final IconData icon;

  const IconContainer(this.icon, {Key? key, this.color = Colors.red})
      : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Container(
      alignment: Alignment.center,
      width: 100,
      height: 100,
      color: color,
      child: Icon(icon, color: Colors.white, size: 28),
    );
  }
}

Expanded

Expanded相当于Android原生的权重。

主要代码：

class MyHomePage extends StatelessWidget {
  const MyHomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return const Column(
      children: [
        Expanded(
          flex: 1,
          child: IconContainer(Icons.home),
        ),
        Expanded(
          flex: 3,
          child: IconContainer(
            Icons.ac_unit,
            color: Colors.orange,
          ),
        ),
        Expanded(
          flex: 3,
          child: IconContainer(
            Icons.android,
            color: Colors.green,
          ),
        ),
      ],
    );
  }
}

flex属性相当于Android原生的layout_weight权重属性。

完整代码：

import 'package:flutter/material.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData(primarySwatch: Colors.blue),
      home: Scaffold(
        appBar: AppBar(
          title: const Text("Flutter"),
        ),
        body: const MyHomePage(),
      ),
    );
  }
}

class MyHomePage extends StatelessWidget {
  const MyHomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return const Column(
      children: [
        Expanded(
          flex: 1,
          child: IconContainer(Icons.home),
        ),
        Expanded(
          flex: 3,
          child: IconContainer(
            Icons.ac_unit,
            color: Colors.orange,
          ),
        ),
        Expanded(
          flex: 3,
          child: IconContainer(
            Icons.android,
            color: Colors.green,
          ),
        ),
      ],
    );
  }
}

class IconContainer extends StatelessWidget {
  final Color color;
  final IconData icon;

  const IconContainer(this.icon, {Key? key, this.color = Colors.red})
      : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Container(
      alignment: Alignment.center,
      width: 100,
      height: 100,
      color: color,
      child: Icon(
        icon,
        color: Colors.white,
        size: 28,
      ),
    );
  }
}

SizedBox

SizedBox容器和Container容器类似，都可以用来装载控件，只是自带属性不一样，可以根据布局视情况而定。

完整代码：

import 'package:flutter/material.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData(primarySwatch: Colors.blue),
      home: Scaffold(
        appBar: AppBar(
          title: const Text("Flutter"),
        ),
        body: const MyHomePage(),
      ),
    );
  }
}

class MyHomePage extends StatelessWidget {
  const MyHomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return ListView(
      children: [
        SizedBox(
          width: double.infinity,
          height: 200,
          //设置网络图片
          child: Image.network(
            "https://www.itying.com/images/flutter/1.png",
            //fill:拉伸填充，父容器无留白，图片变形
            //contain:容纳，父容器有留白
            //cover:剪裁填充，父容器无留白
            //fitWidth:横向剪裁填充，可能有留白
            //fitHeight:纵向剪裁填充，可能有留白
            //none:全无，剪裁，可能有留白
            //不设置此属性:不剪裁，有留白
            //scaleDown:按比例缩放，有留白
            fit: BoxFit.cover,
          ),
        ),
        const SizedBox(height: 2),
        Row(
          children: [
            Expanded(
              flex: 3,
              child: SizedBox(
                height: 180,
                child: Image.network(
                  "https://www.itying.com/images/flutter/2.png",
                  fit: BoxFit.cover,
                ),
              ),
            ),
            Container(
              width: 2,
            ),
            Expanded(
              flex: 1,
              child: SizedBox(
                height: 180,
                child: Column(
                  children: [
                    Expanded(
                      flex: 1,
                      child: Image.network(
                        "https://www.itying.com/images/flutter/3.png",
                        fit: BoxFit.cover,
                      ),
                    ),
                    Container(
                      height: 2,
                    ),
                    Expanded(
                      flex: 1,
                      child: Image.network(
                        "https://www.itying.com/images/flutter/4.png",
                        fit: BoxFit.cover,
                      ),
                    ),
                  ],
                ),
              ),
            )
          ],
        )
      ],
    );
  }
}

Image.network中的fit属性相当于ImageView中的scaleType属性，具体用法请看上面代码注释或者看源码注释。

Stack

完整代码：

import 'package:flutter/material.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData(primarySwatch: Colors.blue),
      home: Scaffold(
        appBar: AppBar(
          title: const Text("Flutter"),
        ),
        body: const MyHomePage(),
      ),
    );
  }
}

class MyHomePage extends StatelessWidget {
  const MyHomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    //Stack:堆叠，相当Android原生的帧布局
    return Stack(
      alignment: Alignment.center,
      children: [
        Container(
          width: double.infinity,
          height: 300,
          color: Colors.green,
        ),
        Container(
          width: 200,
          height: 200,
          color: Colors.red,
        ),
        const Text("你好Flutter")
      ],
    );
  }
}

Stack:堆叠，相当Android原生的FrameLayout帧布局。

Positioned

Positioned:定位布局相当于Android原生中的RelativeLayout相对布局。

完整代码：

import 'package:flutter/material.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData(primarySwatch: Colors.blue),
      home: Scaffold(
        appBar: AppBar(
          title: const Text("Flutter"),
        ),
        body: const MyHomePage(),
      ),
    );
  }
}

class MyHomePage extends StatelessWidget {
  const MyHomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Container(
      width: double.infinity,
      height: 300,
      color: Colors.red,
      //Stack:堆叠
      child: Stack(
        children: [
          //Positioned:定位
          Positioned(
            left: 0,
            bottom: 0,
            child: Container(width: 100, height: 100, color: Colors.green),
          ),
          const Positioned(left: 0, bottom: 0, child: Text("你好Flutter"))
        ],
      ),
    );
  }
}