dart学习之旅-白红宇

dart学习之旅

阅读量：261 次

发布时间：2019-03-01

本文共 1619 字，大约阅读时间需要 5 分钟。

//基本的dart程序// Define a function.void printInteger(int aNumber) {  print('The number is $aNumber.'); // Print to console.}// This is where the app starts executing.void main() {  var number = 42; // Declare and initialize a variable.  printInteger(number); // Call a function.}

// 表示lineCount默认为空值

int? lineCount;

//late 变量的使用late String description;void main() {  description = 'Feijoada!';  print(description);}

Final and const

实例变量只能是Final

Dart常用内置数据类型：

(int, double)

(String)

(bool)

(List, also known as arrays) 范型的用法循环

(Set)

(Map)

Runes代表字符串的UTF-32字符集, Unicode为每一个字符、标点符号、表情符号等都定义了一个唯一的数值
```
runesDemo() {  Runes runes = new Runes('\u2665, \u{1f605}, \u{1f60e}');  print(runes);  print(new String.fromCharCodes(runes));}
```

The value null (Null)

其他数据类型：Object，Future and Stream（用于异步操作），Iterable，dynamic，void。

Lists 初始化：var list = [1, 2, 3];

Sets

var names = 
   
    {};// Set
    
      names = {}; // This works, too.// var names = {}; // Creates a map, not a set.

函数

enableFlags(paramName: value, hidden: false);

可选参数：String say(String from, String msg, [String? device])

缺省参数值：void enableFlags({bool bold = false, bool hidden = false}) {...}

//将函数做为参数void printElement(int element) {  print(element);}var list = [1, 2, 3];// Pass printElement as a parameter.list.forEach(printElement);

条件表达式：

condition ? expr1 : expr2

expr1 ?? expr2

连续操作运算符（级连）

var paint = Paint()  ..color = Colors.black  ..strokeCap = StrokeCap.round  ..strokeWidth = 5.0;

//类的定义class Point {  double x = 0;  double y = 0;  // Syntactic sugar for setting x and y  // before the constructor body runs.  Point(this.x, this.y);}