Summary of Dart basic knowledge points

1. Dart syntax

1. Development tools

Vscode, install plug-ins: dart, Code Runner

2. Entry method

main(){
  print('你好，dart');
}
// 表示main方法没有返回值
void main(){
  print('你好，dart');
}

3 .Dart variables

Dart is a powerful scripting language that does not need to predefine types and will automatically infer types

Variables defined in dart can be declared through the var keyword

There is type checking in dart

Such as:

var str = 'this is var';
String str = 'this is string';
int str = 123;

4. Dart variables

Final const can define constants

Final can be started without assignment , can only be assigned once; and final not only has the characteristics of const compile-time constants, but the most important thing is that it is a run-time constant, and final is lazy initialization, that is, it is initialized before the first use at run-time

Such as:

const NUM = 123;
final Time = new DateTime.now();

5.Dart data type

Numbers: int double

Strings: String

如：var str = 'this is a string';
   String str = 'this is a string';
   // 定义多行字符串
   String str = '''
     my name is wq;
     my age is 23;
   ''';
   // 字符串拼接
   String name = 'wq';
   int age = 23;
   String myInfo = '我的名字叫$name,我今年$age岁';
   // 注意：如果使用+实现字符串拼接，那么必须要是同类型的数据
   String firstName = '王';
   String lastName = '清';
   String myInfo = lastName + ':' + firstName;

Booleans( Boolean): bool

  bool flag = true;

List (list): It is an array in js

// 第一种定义List的方式
  var list1 = [1,2,3];
  print(list1.length);
// 第二种定义List的方式
  var list = new List();
  list.add(1);
  list.add(2);
// 定义List指定元素类型
    var list = new List<String>();
   list.add(&#39;王清&#39;);

Maps (dictionary): Map is an object related to key-value pairs

// 第一种定义Map
  var person = {
    "name": "王清",
    "age": 23
  };
  print(person['name']);
// 第二种定义Map
  var p = new Map();
  p['name'] = '王清';
  print(p);
 问：如何判断类型？(关键字 is)
    var str = '123';
    if (str is String) {
       print('字符串类型');
    } else if (str is int) {
       print('数值类型');
    }
   注意：
    取整运算符 
      如：print(12~/5); // 2
    为空赋值  
      如：int b; b??=23; print(b);  // 23
      解释：如果b为空的话就赋值23
      int a;  int b = a??10;  print(b); // 10

6 .Type conversion

1) Conversion between Number and String types

①Number is converted to String type toString()

int num = 12;
print(num.toString());

②String is converted to Number type parse

String str = '123';
print(int.parse(str));
print(double.parse(str));

2) Convert other types to Booleans type

①isEmpty：判断当前字符串是否为空
   String str = '';
    print(str.isEmpty);
②未赋值 var myNum; print(myNum == null); // true
③为0 var myNum=0; print(myNum ==0);  // true
④为NaN var myNum = 0/0; print(myNum.isNaN); // true

7.List

Common attributes:

length: length

reversed: flip

var list = [1,2,3];

print(list.reversed.toList());

isEmpty: whether it is empty

isNotEmpty : Whether it is not empty

Commonly used methods:

add(): Add an element, only one element can be added

addAll(): Splice the list list.addAll([ 1,2,3])

                                                                            indexOf(): Search the data, find the subscript of the returned element, if not found,                                                                                                                                                                             

Set set1 = [1,2,3].toSet();
Set set2 = [2,3,4].toSet();
print(set1.union(set2).toList()); // [1,2,3,4]

Set set1 = [1,2,100,200,300,3].toSet();
var list = set1.firstWhere((value){
     return value > 100;
});
print(list); // 200

Set set1 = [1,2,100,200,300,3].toSet();
var list = set1.firstWhere((value){
   return value > 100;
});
print(list); // 300

Set set1 = [1,2,100,200,300,3].toSet();
set1.removeWhere((value){
   return value > 100;
});
print(set1);  // {1, 2, 100, 3}

Set set1 = [1,2,100,200,300,3].toSet();
set1.retainWhere((value){
   return value > 100;
});
print(set1);  // {200，300}

Set set1 = [1,2,100,200,300,3].toSet();
set1.retainAll([1,2]);
print(set1); // {1，2}

Set set1 = [1,2,100,200,300,3].toSet();
set1.removeAll([1,2]);
print(set1); // {100,200,300,3}

// 方法一
List list = [1,2,3,4,1,2];
Set s = new Set();
s.addAll(list);
print(s.toList());
// 方法二
List list = [1,2,3,4,1,2];
print(list.toSet().toList());

};

                                                                                                                                                                                                                                       # ：Whether the key-value pair of the value exists in the Map

                                                                                                                               . # For example: m.containsKey("name")

10. forEach map where any every (common to List, Set, Map)

General loop:

List list = [100,200,300,400];

for(var i in list){

print(i); // 100 200 300 400

}

forEach loop ：

List list = [100,200,300,400];

list.forEach((value) => print(value));

list.forEach((value){

PRINT (VALUE); // 100 200 300 400

});

Map Cycle:

                  print(printUserInfo('Wang Qing', 20)); #                                                                                                                                                                                                                                                                                        . }

#}

# Print (Printuserinfo ('Wang Qing'));

## ⑤ Anonymous method

Function fn = () {

Return 'I am an anonymous function'

};

## This.age.age = age;

                                                                                                                                                                                                                    . int age){

                                  this.name = name;                                   this.age =  

Person (this.name, this.age);

void getinfo () {

PRINT ("$ {this.name} --- $ {this. age}");

            p2.getInfo(); Class

2. Quote

import 'person.dart';

void main () {

Person P = New Person.now (' Wang Qing',23);

                p.getInfo(); There are no access modifiers such as private, public, and protected

But we can use _ to define a property or method as private

Private properties or methods cannot be instantiated and called directly, and can only be called internally New methods or properties to use

The function can be abbreviated as follows

Person(this._name,this.age);

// Named constructor

Person.now(String name,int age) {

                                                                                                                                                                                                                              this. print ("${this._name}---${this.age}");

                                                                                                                                                      Extracted into a file

1) Getter and setter modifiers in the class:

class Rect{

num height;

num width;

Rect(this.height,this.width);

set areaWidth(value){

this.height = value;

}

            get area{

                                                                                                                                      using                   using                   ’ s through     ’s   through     ’s   through     ’s out through  through through  through through through‐ over through through over‐‐to‐‐‐‐‐‐ trail to return this.height * this.width;

# Rect r = new Rect(10, 10);

// Call the get modified method by accessing the property

Print(r.area);

// Call set to assign a value to the property by assigning a value

          r.areaWidth = 20;

              print(r.area); 2) In Dart, instance variables can be initialized before the constructor body is run. class Rect{

num height;

num width;

Rect() ;

## 3) Static members

①Use the static keyword to implement class-level variables and functions

②Static methods cannot access non-static members, and non-static methods can access static members

Class Person {

Static String name = 'Wang Qing';

static void show () {

# PRINT (name);

}

..show ();

#                                                                                     class Web extends Person{

                  String sex;

                                                this.sex = sex; #                   void run(){

PRINT ('Running');

                                                                                                                                                                                              'PRINTINFO');

# Abstract classes in Dart: Dart abstract classes are mainly used to define standards. Subclasses can inherit abstract classes or implement abstract class interfaces

①Abstract classes are defined through the abstract keyword

② The abstract method in Dart cannot be declared by Abstract. There is no method of method in Dart. The abstract class should be achieved as the interface implementation. All methods and attributes are defined in the abstract class

# ⑤ The abstract class cannot be instantiated. Difference:

① If you want to repeat the method in the abstract class, and use the abstract method to restrain the self -class painting, we use Extends to inherit the abstract class

② For standard purposes, we use implements to implement the abstract class

Abstract class:

Abstract class Animal{

void eat(); // Abstract method

void drink(){

                                                                                                                                                 print('I want to drink water'); #                                                                                                                 void eat(){                                                                                                        void eat() @override

void drink () {

# PRINT ('Drinking water');

}

void run () {

## // a.run(); Error

      }

                                                                       ’ ’s Error's ’       ‐       ‐   ‐ ‐                                                                         using   using       to ‐ to have

         abstract class DB{

                       String URL; class MySQL implements DB{

                                                        ’ ’s ’ s           ’ through ’ s ’   ’ way through ‐ ‐ ‐ ‐ ‐ ‐                               ‐                           to Return null;

# Conditions for using mixins:

① Classes as mixins can only inherit from Object and cannot inherit from other classes

② Classes as mixins cannot have constructors

③A class can mixins multiple mixins classes

④Mixins are neither inheritance nor interfaces, but a brand-new feature

Such as:

class A{

                        void printA(){

                print('A'); #Void Printb () {

# Print ('B');

}

## Class C Extends A with b {

#     }

          class D with A,B{

          }

                                              ’’s ’         through ’ through ’'s ’   through ’ through ’ s ’ through ’' ‐    ‐  ‐ ‐ ‐ ‐ void main(){

          C c = new C();

                                                                                                                                                                                                                                                                c.