Dart Language Tutorial

1.Coding Standards

almost exactly the same asC/C++.

• 扩展名： dart语言文件后缀以.dart结尾
• 入口：dart文件的入口方法为main方法
• 分号：dart文件中绝大部分语句都需要加分号结尾，像 { } 后通常不加分号

2.Dart variables

This section is highly similar toC/C++.

2.1.String type - String

andC/C++instd::stringessentially similar.

Basic usage:

• Keyword: String
• Syntax:String 属性名 = ‘文本内容’;
• Features: Supports double quotes or single quotes, and supports concatenation and template strings

Advanced usage:

• Syntax:String 属性名 = ‘文本内容$变量名’; or String 变量名 = ‘文本内容${变量名}’;
• Note: When the content in the template is an expression, use ${}, whether it is an expression or a variable, it is more recommended to use ${}, and try to avoid using $变量名.

void main()
{
  String name = 'Alice';
  print(name); // Output: Alice

  name = 'Bob';
  print(name); // Output: Bob

  String greeting = 'Hello, ${name}?$name!';
  print(greeting); // Output: Hello, Bob?Bob!

  String when = 'it is ${DateTime.now()},now';
  print(when); // Output: it is 2026-02-16 14:46:17.818262,now
}

2.2.数字类型-int/double/num

与C/C++中的int,double基本类似.

Basic Syntax

• Scenario: When we need to describe a numeric type, we need to use int/num/double
• Difference: int - integer number, double - decimal, num - can be integer or decimal
• Syntax:int/num/double 属性名 = 数值;

void main()
{
  int age = 23;
  print(age); // Output: 23

  age = 24;
  print(age); // Output: 24

  double height = 1.78;
  print(height); // Output: 1.78

  height = 1.80;
  print(height); // Output: 1.8

  num weight = 90.5;
  print(weight); // Output: 90.5

  weight = 76;
  print(weight); // Output: 76
}

Essential differences among the three:

num
 ├── int
 └── double

• 👉 num is the parent class
• 👉 int and double are subclasses

Summary table of direct assignment rules:

Although direct assignment is not possible, it can be converted before assignment. This can be achieved using methods such as toInt() and toDouble() , for example:

void main()
{
  int a = 10;
  print(a); // Output: 10

  double b = 3.14;
  print(b); // Output: 3.14
  
  // double赋值给double
  double c = b;
  print(c); // Output: 3.14

  // int赋值给double
  b = a.toDouble();
  print(b); // Output: 10.0

  num d = 5.6;
  print(d); // Output: 5.6

  // num赋值给int
  a = d.toInt();
  print(a); // Output: 5

}

2.3.Boolean type - bool

Similar toC/C++inboolis basically similar.

• Scenario: When we need an attribute to represent whether something is currently true or false, we need to use the bool keyword to declare it.
• Requirement: Declare whether you have already finished your homework.
• Syntax:bool 属性名 = true/false;

void main()
{
  bool isFinishWork = false;
  print('我的工作完成状态为：$isFinishWork'); //Output: 我的工作完成状态为：false
  
  isFinishWork = true;
  print('我的工作完成状态为：$isFinishWork'); //Output: 我的工作完成状态为：true
}

2.4.List Type - List

2.4.1.List

Similar toC/C++the vectors inSTL.(Note, unlikestd::vectorandstd::list) Andstd::vectorwe often use it as不定长数组, so when you don't understandstd::vectorjust treat it as an advanced数组and that's fine.

本节肯定讲不完List的所有用法,但是大多数常用的用法都会讲到,你忘记了可以随时去查文档就行,不用每种用法都硬背下来,用的多的用法自然你就记住了,现在你只需要学完一遍,并知道有那么个东西即可.

Basic usage:

• 场景：当一个变量需要存储多个值的时候，可以使用列表类型List
• 需求：一个班级的学生用List存储，支持对学生的查找、新增、删除、循环
• 语法：List 属性名 = [‘学生1’, ‘学生2’];

Common usage 1:

• Append at tail -add(内容)
• Append a list at tail -addAll(列表)
• Delete the first matching content -remove(内容)
• Delete the last -removeLast()
• Delete data within index range -removeRange(start,end) Note: end is not included in the deletion range

Common usage 2:

Below, several methods and properties will be listed. If you have studied object-oriented programming, you definitely know what they are; if not, I'll briefly explain first:

类-class的声明与定义
对象-class类型的实例,(不好理解也可以理解为class类型的变量)
方法-class里的函数
属性-class里的变量

• Loop (method) -forEach((item) {});
• Whether all conditions are met (method) -every((item) { return 布尔值 })；
• Filter out data that meets the conditions (method) -where((item) { return 布尔值 })；
• Length of list (property) -length
• Last element (property) -last
• First element (property) -first
• Whether it is empty (property) -isEmpty

void main(List<String> args) 
{
  List students = ["张三", "李四", "王五"];
  print(students); // Output: [张三, 李四, 王五]

  students.add("新同学"); // 在尾部进行添加
  print(students); // Output: [张三, 李四, 王五, 新同学]s

  students.addAll(["新来的同学1", "新来的同学2"]); // 在尾部添加一个列表
  print(students); // Output: [张三, 李四, 王五, 新同学, 新来的同学1, 新来的同学2]

  students.add("新同学"); // 在尾部进行添加
  print(students); // Output: [张三, 李四, 王五, 新同学, 新来的同学1, 新来的同学2, 新同学]

  students.remove("新同学"); // 删除满足内容的第一个
  print(students); // Output: [张三, 李四, 王五, 新来的同学1, 新来的同学2, 新同学]

  // 删除最后一个同学
  students.removeLast(); // 删除最后一个
  print(students); // Output: [张三, 李四, 王五, 新来的同学1, 新来的同学2]

  // 删除前两个同学
  // start开始的索引 end结束的索引-不包含在删除范围内
  students.removeRange(0, 2);
  print(students); // Output: [王五, 新来的同学1, 新来的同学2]

  // forEach针对每个列表每个数据进行操作
  students.forEach((item) 
  {
    // 书写逻辑
    print(item); // Output: 王五
                 //         新来的同学1
                 //         新来的同学2
  });

  // 是不是所有的同学都以新为开头
  bool isAllStartWithNew = students.every((item) 
  {
    return item.toString().startsWith("新"); // 返回一个条件
  });
  print(isAllStartWithNew); // Output: false (因为王五不以新开头,需要满足所有的同学都以新开头才会返回true)

  // 筛选出所有的以新开头的同学呢
  List newStudents = students.where((item) 
  {
    return item.toString().startsWith("新");
  }).toList();
  print(newStudents); // Output: [新来的同学1, 新来的同学2]


  // List常用的一些属性 方法() .属性
  // 列表的长度
  print(students.length); // Output: 3

  // 列表的第一个
  print(students.first); // Output: 王五

  // 列表的最后一个
  print(students.last); // Output: 新来的同学2

  // 列表是否是空的
  print(students.isEmpty); // Output: false (因为列表中有数据)
}

2.4.2.main function entry parameters

In addition to the above code, it can be seen thatvoid main(List<String> args)now contains a parameter, which is actually similar toC/C++inint main(int argc, char* argv[])

For example

dart run app.dart hello world

At this time

args[0] = "hello"
args[1] = "world"

2.5.Dictionary type - Map

Similar to C++std::map.

Basic usage:

• One key corresponds to one value
• Syntax 1: Map propertyName = { key: value };
• Syntax 2: 字典[key] 可以取值和赋值

Common usage:

• Loop-forEach
• Add a dictionary-addAll
• Whether it contains a certain key-containsKey
• Delete a certain key-remove
• Clear-clear

void main(List<String> args) 
{
  Map transMap = {"lunch": '午饭', "morning": "早上", "hello": '你好'};
  print(transMap);
  // 通过英文找到对应中文的描述
  print(transMap["morning"]);
  transMap["hello"] = "你非常好";
  print(transMap["hello"]);
  // 字典里面有很多对应关系
  transMap.forEach((key, value) {
    print("$key,$value");
  });
  // addAll 给当前字典添加一个字典
  transMap.addAll({"fine": "非常好"});
  print(transMap);
  // containesKey判断字典中是否包含某个key
  print(transMap.containsKey("fine"));

  transMap.remove("fine");
  print(transMap);

  // 清空字典
  transMap.clear();
  print(transMap);
}

2.6.Dynamic Type - dynamic

Similar to C++std::any

• Definition: In the Dart language, dynamic is used to declare a dynamic type.
• Feature: Allows a variable to freely change its type at runtime, while bypassing compile-time static checks.
• Syntax 1:dynamic 属性名 = 值;

void main(List<String> args) 
{
  // dynamic 可以动态的改变类型
  dynamic name = "张三";
  print(name);
  name = 123;
  print(name);
}

Only when you yourself are 100% sure that what you wrote is correct should you use dynamic; otherwise, do not use dynamic, or many errors may occur.

2.7.Automatically inferred type - var

similar to C/C++auto.

This keyword can automatically deduce the type of a variable.

• Keyword: var
• Syntax:var 变量名 = 值/表达式;
• Note: For a variable declared with var, its type is determined after the first assignment, and values of other types cannot be assigned afterward.

void main(List<String> args) 
{
  var name = '张三';
  print(name); // Output: 张三

  name = '李四';
  print(name); // Output: 李四

  var age = 30;
  print(age); // Output: 30

  var isStudent = true;
  print(isStudent); // Output: true

  var height = 1.75;
  print(height); // Output: 1.75
}

Dynamic Types in Dart - The Difference Between dynamic and var:

• dynamic: The type can be freely changed at runtime, with no compile-time checking; methods and properties can be called directly.
• var: The type is inferred from the initial value; once the type is determined, it is fixed, with compile-time checking, and only the inferred properties and methods are allowed.

2.8.常量声明-const/final

2.8.1.const

Similar to C++constexpr.

• 关键字：const
• 语法：const 属性名 = 值/表达式;
• 特点：const是代码编译前被确定，不允许表达式中有变量存在，必须为常量或者固定值

void main(List<String> args) 
{
  const int a = 10;
  const double b = 3.14;
  const String c = "Hello, Dart!";

  print("Value of a: ${a}"); // Output: Value of a: 10
  print("Value of b: ${b}"); // Output: Value of b: 3.14
  print("Value of c: ${c}"); // Output: Value of c: Hello, Dart!
}

2.8.2.final

similar to C++const.

• 关键字：final
• 语法：final 属性名 = 值/表达式;
• 特点：final变量在运行时被初始化，其值设置后不可更改

void main(List<String> args) 
{
  final time = DateTime.now();
  print('Current time: $time'); // Current time: 2026-02-16 20:53:53.045010
}

• Variable: When you need to store changing data, you need to use var to declare a variable.
• Compile-time constant: When you need to store unchanging data that is determined at compile time, you need to use const to declare a constant.
• Runtime constant: When you need to store unchanging data that is determined only at runtime, you need to use final to declare a constant.

3.Null safety mechanism

• Definition: In the Dart language, runtime null pointer issues are exposed in advance through compile-time static checks
• Feature: Moves null pointer exceptions from runtime to compile time, reducing production crashes

Common null safety operators