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📝 [Flutter] learning to form a record, [programmer essential knowledge]

📔 Today’s tip — Inheritance of Flutter in Dart!

1. Write at the front

You introduced class methods and object operators in Dart in the previous article, so let’s move on to learning about inheritance in Dart.

The Apple Mac is configured with the Flutter development environment

Android Studio installs a third-party simulator for Flutter — netease MuMu

Failed to find Build Tools Revision 29.0.2

Android license status unknown. Run ‘Flutter doctor — Android – Licenses’

How to create a Flutter project and run your first Flutter project

Dart uses var, final, and const

Dart Indicates the num of the data type

Dart String of data type

Dart data type list&Map

Dart method and arrow function

Dart’s method passes optional parameters and methods as parameters

Dart, Dart, Dart, Dart

Dart classes and objects in Flutter

Dart constructor of Flutter

Dart factory constructor & singleton & Initializer list

Dart class methods and object operators for Flutter

2. The inheritance

Inheritance is a common term in object-oriented development languages, and is often used for code reuse in iOS. How is inheritance defined and used in DART?

  • In the Dart
  1. Inherit a class using Extens
  2. Subclasses inherit properties and methods in addition to the constructor
  3. Dart is single inheritance

So let’s look at the code in detail. Define a Person class. Student inherits the Person class.

class Student extends Person {
  study(){
    print("Study hard and make progress every day."); }}class Person {
  String? name;
  int? age;
  int? _height;
  // Calculate attributes
  bool get isRight => _height! > 180;
  run(){
    print("run....."); }}Copy the code

2.1 Subclasses inherit the attributes and methods of their parent class

  • Subclasses inherit the attributes and methods of their parent class
void main(a) {
  Student stu = Student();
  stu.name = "reno";
  stu.run();
  stu._height = 181;
  stu.study();
  print(stu.isRight);

}
Copy the code
  • Print the result

2.2 Subclasses override superclass methods

  • A subclass overrides a parent class method
@override
  run(a){
    print("Student run..");
  }
Copy the code

Overriding the parent class method is the same as Swift using Override.

2.3 polymorphic

  • polymorphism
 / / polymorphism
  Person stu = Student();
  if(stu is Student) {
    stu.name = "reno";
    stu.run();
    stu._height = 181;
    stu.study();
    print(stu.isRight);
  }
Copy the code
  • The test results

All classes inherit from Object, so the Person class looks like this:

class Person extends Object{
}
Copy the code

Object has a toString() method similar to description in OC. Now rewrite toString() :

ToString () by default returns the value super.toString(), which can be customized

2.4 About the construction method

  • A constructor

The default constructor of the parent class is inherited by default, but the constructor of the parent class is not inherited by default, and the constructor of the parent class is implemented manually. If there are multiple, the child class can implement one of them manually, as follows:

The subclass does not implement any constructors other than the default.

3. Write in the back

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