Flutter使用小技巧一（持续更新）

16进制颜色转换

//如果颜色固定可以直接使用整数值
Color(0xffdc380d); 
//颜色是一个字符串变量
var c = "dc380d";
//通过位运算符将Alpha设置为FF（透明度，完全不透明）
Color(int.parse(c,radix:16)|0xFF000000) 
//通过方法将Alpha设置为FF
Color(int.parse(c,radix:16)).withAlpha(255)  

final、const的区别

final 编译时不确定，运行时确定值 final curTime=DateTime.now()
const 编译时即明确的值 
~~const curTime=DateTime.now()~~   
fix： const curTime='2022-12-12' 

Text/RichText行间距

style: const TextStyle(
    //可作为行间距
    height: 1.7,
    fontSize: 15.0,
    color: Color(0xFFb7b7b7),
    fontFamily: 'QuicksandMedium'),

TextSpan点击事件

  late TapGestureRecognizer _gestureRecognizer;
  
  @override
  void initState() {
    super.initState();
    _gestureRecognizer = TapGestureRecognizer();
  }

  @override
  void dispose() {
    _gestureRecognizer.dispose();
    super.dispose();
  }

Container(
  alignment: Alignment.center,
  margin: const EdgeInsets.only(top: 28.0),
  child: Text.rich(
    TextSpan(text: "By continuing, you agree to ", children: [
      const TextSpan(
          text: 'Terms of Service',
          style: TextStyle(decoration: TextDecoration.underline)),
      const TextSpan(text: ' and '),
      TextSpan(
          recognizer: _gestureRecognizer
            ..onTap = () {
              showDeleteConfirmDialog(context);
            },
          text: 'Privacy Policy',
          style:
              const TextStyle(decoration: TextDecoration.underline)),
    ]),

Dart构造参数不允许开头使用_

class Counter extends StatelessWidget {
  final int count;

  const Counter({Key? key, required this.count}) : super(key: key);

…联级表示法

类比Builder模式

class User {
  String? name;
  int age = 0;
}

var user=new User()
user
  ..name = 'TR'
  ..age = 10;

空安全运算符

?

若你想让变量可以为 null，只需要在类型声明后加上 ?

int? aNullableInt;

?.

等同于

xx?.login();
if（xx!=null）{
   xx.login();
}

!

用强制非空操作符

[]

可选填的位置参数

void request(String url,[String ?path])

??

print(user?.name ?? '结果为null');

等价

if(user==null||user.name==null){
    print('结果为null');
}else{
    print('user.name');
}

final ValueChanged<bool?>? onChanged;
onChanged??(value);

如果name为空则返回default

String ? name;
name??'default'

extension on 扩展方法

extension ExtensionName on String {
  int string2Int() {
    return int.parse(this);
  }
}

全局设置动画放慢倍数（测试时可验证动画效果）

import 'package:flutter/scheduler.dart' show timeDilation;

使用：
timeDilation=5.0; 放慢5倍

或者

设置widget占满屏幕

Container(
  //方法1
  //constraints: const BoxConstraints.expand(),
  //方法2
  height: double.infinity,
  width: double.infinity,
),

const BoxConstraints.expand({
    double? width,
    double? height,
  }) : minWidth = width ?? double.infinity,
       maxWidth = width ?? double.infinity,
       minHeight = height ?? double.infinity,
       maxHeight = height ?? double.infinity;

Column/Row中插入Column/Row

...的使用

常规写法：Column(children: buttons,)
简写：...buttons

child: Column(
  crossAxisAlignment: CrossAxisAlignment.start,
  children: [
    const Spacer(),
    ...buttons,
    Text(
      recipes.name!,
      maxLines: 3,
      style: const TextStyle(
          color: Colors.white,
          fontSize: 24.0,
          fontFamily: 'RobotoSlabBold'),
    ),
    ...
  ],
)),

  List<Widget> buttons = [...];

状态栏/底部导航栏颜色

void main() {
  if (Platform.isAndroid) {
    SystemChrome.setSystemUIOverlayStyle(const SystemUiOverlayStyle(
      statusBarColor: Colors.blue,
      systemNavigationBarColor: Colors.red
    ));
  }

  runApp(GetMaterialApp(
    home: const Home(),
    theme: ThemeData(primarySwatch: Colors.red),
  ));
}

LayoutBuilder获取屏幕当前信息

child: LayoutBuilder(
  builder: (BuildContext context, BoxConstraints constraints) {
    return Container(
        color: Colors.blue,
        width: constraints.maxWidth / 2,
        height: constraints.maxHeight / 2);
  },
),

DefaultTextStyle的使用

//子TextWidget都会继承DefaultTextStyle
//DefaultTextStyle.merge()可以继承parent的style 
  child: DefaultTextStyle(
style: const TextStyle(
    fontSize: 24, fontFamily: 'RobotoSlabBold', color: Colors.red),
child: Column(
  children: [
    const Text('Kotlin'),
    const Text('Python'),
    //java不继承DefaultTextStyle
    Text('Java', style: Theme.of(context).textTheme.bodyText1)
  ],
),
),

InteractiveViewer 实现滑动、缩放

//可上下左右滑动并且支持缩放的widget
body: InteractiveViewer(
  //不再约束子布局
  constrained: false,
  //最大放大倍数
  maxScale: 5.0,
  child: SizedBox(
    height: MediaQuery.of(context).size.height,
    width: MediaQuery.of(context).size.width,
    child: Text(
        'Browse our range of delicious recipes created by chefs who always have you in mind.' *
            100),
  ),
)),