Google Dart编程语法和基本类型学习教程

admin Dart

2023-12-07 0 327

1. 变量声明

如何定义变量

复制代码代码如下:var name = \’Bob\’;

变量的初始值

复制代码代码如下:int lineCount;assert(lineCount == null); // Variables (even numbers) are initially null.

可以使用var，也可以直接指定类型。final，定义为final的变量，值不能够被更改

复制代码代码如下:final name = \’Bob\’; // Or: final String name = \’Bob\’;name = \’Alice\’; // ERROR

2. 基础类型

字符串字符串可以使用单引号或者双引号。复制代码代码如下:var s1 = \’Single quotes work well for string literals.\’;var s2 = \”Double quotes work just as well.\”;在字符串中，可以直接应用值， ${表达式}，如果只是一个变量，就可以去掉{}复制代码代码如下:var s = \’string interpolation\’;assert(\’Dart has $s, which is very handy.\’ == \’Dart has string interpolation, which is very handy.\’);assert(\’That deserves all caps. ${s.toUpperCase()} is very handy!\’ == \’That deserves all caps. STRING INTERPOLATION is very handy!\’);多行字符串，会被认为默认拼接。复制代码代码如下:var s = \’String \’\’concatenation\’ \” works even over line breaks.\”;assert(s == \’String concatenation works even over line breaks.\’);

如果要使用多行字符串，可以这样, 用\’\’\’复制代码代码如下:var s1 = \’\’\’You can createmulti-line strings like this one.\’\’\’;创建一个不考虑转义的字符串复制代码代码如下:var s = @\”In a raw string, even \\n isn\’t special.\”;

StringBuffer, 非常类似.net中的。复制代码代码如下:var sb = new StringBuffer();

sb.add(\”Use a StringBuffer \”);sb.addAll([\”for \”, \”efficient \”, \”string \”, \”creation \”]);sb.add(\”if you are \”).add(\”building lots of strings.\”);

var fullString = sb.toString();

数字

主要就2种，int 和 double, 它们都继承num类型

数字和字符串之间的转换

复制代码代码如下:// String -> intvar one = Math.parseInt(\”1\”);assert(one == 1);

// String -> doublevar onePointOne = Math.parseDouble(\”1.1\”);assert(onePointOne == 1.1);

// int -> Stringvar oneAsString = 1.toString();assert(oneAsString == \”1\”);

// double -> Stringvar piAsString = 3.14159.toStringAsFixed(2);assert(piAsString == \”3.14\”);布尔类型

bool，不同于js, 只要不是true, 那么就都是false.

Lists(可以当做数组)

复制代码代码如下:var list = [1,2,3]; //实例化一个listlist.add(4); //添加一个元素4

可以使用for, for…in, foreach()来遍历一个list.复制代码代码如下:var list = [1,2,3];for (final x in list) { print(x);}或者复制代码代码如下:var list = [1,2,3];list.forEach((element) => print(element));

Maps（字典类型)

复制代码代码如下:var gifts = { // A map literal// Keys Values \”first\” : \”partridge\”, \”second\” : \”turtledoves\”, \”fifth\” : \”golden rings\”};

gifts[\”third\”] = \”apple\”; //添加一个

使用foreach遍历复制代码代码如下:var gifts = { \”first\” : \”partridge\”, \”second\”: \”turtledoves\”, \”fifth\” : \”golden rings\”};gifts.forEach((k,v) => print(\’$k : $v\’));

getKeys()和getValues()方法复制代码代码如下:var gifts = {\”first\”: \”partridge\”, \”second\”: \”turtledoves\”};var values = gifts.getValues();

//Print partridge and turtledoves, but not necessarily in that order.values.forEach((v) => print(v));

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