早上开车等红绿灯时想到几个月前写的一个算法，应该可以更简单，今天重新写了一遍
寻找下一个数字，例如输入345，输出354
思路：从最右边位和上一位对比，如果大，就往前移，移动完，尾数排序，从小到大，保证次大
代码
1 | //字符串分成数组 |
使用：
1 | NSString *str = findNextLargerNum(@"8976"); |
flutter App 优化实操
抽取widget，尽量成为一个stateless widget
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16class MainWidget extends StatelessWidget {
Widget build(BuildContext context) {
return Expanded(
child: Container(
color: Colors.grey[700],
child: Center(
child: Text(
'Hello Flutter',
style: Theme.of(context).textTheme.display1,
),
),
),
);
}
}
更新属性值，用传值的方式
ChangeNotifier
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54//------ ChangeNotifier class ----//
class MyColorNotifier extends ChangeNotifier {
Color myColor = Colors.grey;
Random _random = new Random();
void changeColor() {
int randomNumber = _random.nextInt(30);
myColor = Colors.primaries[randomNumber % Colors.primaries.length];
notifyListeners();
}
}
//------ State class ----//
class _MyHomePageState extends State<MyHomePage> {
final _colorNotifier = MyColorNotifier();
void _onPressed() {
_colorNotifier.changeColor();
}
@override
void dispose() {
_colorNotifier.dispose();
super.dispose();
}
@override
Widget build(BuildContext context) {
print('building `MyHomePage`');
return Scaffold(
floatingActionButton: FloatingActionButton(
onPressed: _onPressed,
child: Icon(Icons.colorize),
),
body: Stack(
children: [
Positioned.fill(
child: BackgroundWidget(),
),
Center(
child: AnimatedBuilder(
animation: _colorNotifier,
builder: (_, __) => Container(
height: 150,
width: 150,
color: _colorNotifier.myColor,
),
),
),
],
),
);
}
}
ValueNotifier
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44class _MyHomePageState extends State<MyHomePage> {
final _colorNotifier = ValueNotifier<Color>(Colors.grey);
Random _random = new Random();
void _onPressed() {
int randomNumber = _random.nextInt(30);
_colorNotifier.value =
Colors.primaries[randomNumber % Colors.primaries.length];
}
void dispose() {
_colorNotifier.dispose();
super.dispose();
}
Widget build(BuildContext context) {
print('building `MyHomePage`');
return Scaffold(
floatingActionButton: FloatingActionButton(
onPressed: _onPressed,
child: Icon(Icons.colorize),
),
body: Stack(
children: [
Positioned.fill(
child: BackgroundWidget(),
),
Center(
child: ValueListenableBuilder(
valueListenable: _colorNotifier,
builder: (_, value, __) => Container(
height: 150,
width: 150,
color: value,
),
),
),
],
),
);
}
}使用const修饰stateless widget，set state不会重复刷新
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12class BackgroundWidget extends StatelessWidget {
const BackgroundWidget();
Widget build(BuildContext context) {
print('building `BackgroundWidget`');
return Image.network(
'https://cdn.pixabay.com/photo/2017/08/30/01/05/milky-way-2695569_960_720.jpg',
fit: BoxFit.cover,
);
}
}
生成列表的时候使用itemExtent属性告诉系统item高度，更高效的滑动
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35class MyHomePage extends StatelessWidget {
final widgets = List.generate(
10000,
(index) => Container(
color: Colors.primaries[index % Colors.primaries.length],
child: ListTile(
title: Text('Index: $index'),
),
),
);
final _scrollController = ScrollController();
void _onPressed() async {
_scrollController.jumpTo(
_scrollController.position.maxScrollExtent,
);
}
Widget build(BuildContext context) {
return Scaffold(
floatingActionButton: FloatingActionButton(
onPressed: _onPressed,
splashColor: Colors.red,
child: Icon(Icons.slow_motion_video),
),
body: ListView(
controller: _scrollController,
children: widgets,
itemExtent: 200,
),
);
}
}
需要动画的子控件设置给AnimatedBuilder的child，避免重复绘制
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Widget build(BuildContext context) {
return Scaffold(
floatingActionButton: FloatingActionButton(
onPressed: _onPressed,
splashColor: Colors.red,
child: Icon(Icons.slow_motion_video),
),
body: AnimatedBuilder(
animation: _controller,
child: CounterWidget(
counter: counter,
),
builder: (_, child) => Transform(
alignment: Alignment.center,
transform: Matrix4.identity()
..setEntry(3, 2, 0.001)
..rotateY(360 * _controller.value * (pi / 180.0)),
child: child,
),
),
);
}
合理使用opacity属性，减少调用setlayer方法，触发离屏渲染
使用fadeTransition
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47class _MyHomePageState extends State<MyHomePage>
with SingleTickerProviderStateMixin {
AnimationController _controller;
int counter = 0;
void _onPressed() {
setState(() {
counter++;
});
_controller.forward(from: 0.0);
}
void initState() {
_controller = AnimationController(
vsync: this, duration: const Duration(milliseconds: 600));
_controller.addStatusListener((status) {
if (status == AnimationStatus.completed) {
_controller.reverse();
}
});
super.initState();
}
void dispose() {
_controller.dispose();
super.dispose();
}
Widget build(BuildContext context) {
return Scaffold(
floatingActionButton: FloatingActionButton(
onPressed: _onPressed,
splashColor: Colors.red,
child: Icon(Icons.slow_motion_video),
),
body: FadeTransition(
opacity: Tween(begin: 1.0, end: 0.0).animate(_controller),
child: CounterWidget(
counter: counter,
),
),
);
}
}
使用animatedOpacity
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35const duration = const Duration(milliseconds: 600);
class _MyHomePageState extends State<MyHomePage> {
int counter = 0;
double opacity = 1.0;
void _onPressed() async {
counter++;
setState(() {
opacity = 0.0;
});
await Future.delayed(duration);
setState(() {
opacity = 1.0;
});
}
Widget build(BuildContext context) {
return Scaffold(
floatingActionButton: FloatingActionButton(
onPressed: _onPressed,
splashColor: Colors.red,
child: Icon(Icons.slow_motion_video),
),
body: AnimatedOpacity(
opacity: opacity,
duration: duration,
child: CounterWidget(
counter: counter,
),
),
);
}
}
完。
sources:
flutter安卓release包代码无法执行
问题描述：
flutter工程打包apk文件后
1 | try { |
这段代码无法执行
原因分析
经过咨询，安卓release包会代码混淆，使用反射会让代码无法精确匹配
解决:
- 使用反射的类不参与混淆，降低安全性
- 不使用反射，改用if判断或者switch case
2.https://blog.csdn.net/guohesheng/article/details/53696652
3.https://www.jianshu.com/p/b5b2a5dfaaf4
感谢王志浩同学提供帮助！
flutter App optimization
avoid costly work in build() since build() can be invoked frequently when ancestor Widgets rebuild
avoid calling setState() high up in the tree
Use the lazy methods, with callbacks,when building large grids or lists, that way only the visible portion of the screen is built at startup time
avoid invoke saveLayer(),including
- opacity widget
- shaderMask
- colorFilter
- Clip
- Text
- addition:Clipping doesn’t call saveLayer() but is still costly
Ways to avoid calls to saveLayer():
- To implement fading in an image, consider using the FadeInImage
- using the border Radius property instead of applying a clipping rectangle
build and display frames in 16ms
build subtree widget once and pass it as a child to the AnimatedBuilder
pre-clip image before animating it
avoid using constructors with a concrete List of children if most of the children are not visible on screen
source:https://flutter.dev/docs/perf/rendering/best-practices
new words
to be continued
grasp
/ɡrɑːsp $ ɡræsp/
verb
1 | 1.I grasped his arm firmly and led him away |
directive
/dəˈrektɪv/
noun
1 | 1.an official oeder or instruction |
proposals for implementing the EU directive on paternity leave
allege
/əˈledʒ/
verb
1 | 1.to say that something is true,although it has not been proved |
The water is alleged to be pollutedted with mercury.
medium
/ˈmiːdiəm/
noun
1 | 1.a way of communicating information and news to people,such as newspapers,television etc |
Advertising is a powerful medium
tenure
/ˈtenjə/
noun
1 | 1.the right to stay permanently in a teaching job |
It’s becoming increasingly difficult to acquire academic tenure
registration
/redʒɪˈstreɪʃən/
noun
1 | 1.the act of recording names on an official list |
the registration of motor vehicles
ratify
[ˈrætɪfaɪ]
verb
1 | to make a written agreement official by signing it |
We hope that the republics will be willing to ratify the treaty.
instantaneous
/ˌɪnstənˈteɪniəs◂/
adj
1 | happening immediately |
modern methods of instantaneous communication
aid
/eɪd/
noun
1 | something such as a machine or tool that helps someone do something |
A video is a useful aid in the classroom
relay
/ˈriːleɪ/
verb
1 | to pass a message from one person to another |
relay something to somebody
semaphore
/ˈseməfɔː $ -fɔːr/
noun
1 | a system of sending messages useing two flags,which you hold in different positions to represent letters and numbers |
circuit
/ˈsɜːkɪt/
noun
1 | a path that forms a circle around an area |
we did a circuit of the old city
magnetism
/ˈmæɡnɪtɪzəm/
noun
1 | the physical force that makes two metal objects pull toward each other or push each other apart |
personal magnetism
squiggle
/ˈskwɪɡəl/
noun
1 | a line with irregular curves |
Shorthand just looks like a series of funny squiggles to me
paradigm
/ˈpærədaɪm/
noun
1 | a very clear example of something |
the basic paradigm of the family tree
patent
/ˈpeɪtnt/
noun
1 | a special document that gives you the right to make or sell a new invention or product that no one else is allowed to copy |
The drugs are protected by patent
refer
/rɪˈfɜː $ -ɜːr/
verb
1 | 1.to mention about something |
We agreed never to refer to the matter again.
flutter无法访问另一个类的全局变量
错误描述:在A类访问B类里的static 变量，永远是初始值，即使已经设置过新值
解决办法：A类import B类头文件时使用绝对路径，不使用系统默认
1 | //错误 |
B类结构
1 | class AppHelper { |
新词：
1 | toy around |
flutter NoMethodError - undefined method `size' for nil:NilClass错误排查
错误描述: pod install时发生错误
1 | ## Error |
解决办法：在flutter目录运行以下命令
1 | flutter clean |
framework not found
问题：在build的时候framework not found
解决：
- 添加需要的framework
- 确定framework齐全的情况下，就是系统添加了冗余的framework编译需求，找到require列表删除即可
1 | project.xcodeproj文件--->显示包内容--->project.pbxproj文件 全局查找删除 |
ps:版本对不上处理方法同理，修改版本号和实际pods下载过来一致
hexo部署文章到github 443问题
问题：
1 | fatal: unable to access 'https://github.com/xxx/xxx.github.io.git/': LibreSSL SSL_connect: SSL_ERROR_SYSCALL in connection to github.com:443 |
解决：在_config.yml文件里把deploy的地址从http换成git
1 | deploy: |
h5优化策略总结
原生webview加载耗时
- 预热webview，并且缓存多个对象进行复用
webview网络请求页面内容，下载html
- 在未点开网页时，用网络请求框架异步请求html内容，保存到本地缓存框架中
- 在移动端启动local web server，同步服务器资源到本地，h5链接替换成localhost+port链接，例如swift版本的Telegraph
- 本地网络框架请求zip资源并解压，供WKWebview的WKURLSchemeHandler拦截网络请求并调用(例如把http替换为自动以scheme)
解析html
- webview请求网络前先本地缓存查找已经下载好的html内容，直接进行加载渲染
请求js、css资源
- 本地网络框架选择性下载较大图片文件
正常页面加载顺序为拿到html，计算布局，识别外链资源，绘制渲染
- 后端直接加载好页面依赖的css，js和接口数据，拼接好一个最终版html返回给前端
接口耗时长
- 更新接口的处理方式
- 增加占位图，优化体验
内存泄露
- 及时释放图片和数组等资源
参考链接：