Dart basic notes

Dart Basics

• dynamic The assignment type can be changed
• var If initialization determines the type , Cannot be changed halfway
• Static type is better than dynamic type High execution efficiency
• final The value cannot be modified , The runtime determines
• const Compile time determines
• final Variables can use const Variable assignment
• dart Can be taken as java Medium int and long Use , If dart More than the 4 Bytes will Translate it into int perhaps long , otherwise Translate it into shot perhaps int
• ??= Sentenced to empty
• … Cascade The operator , It can achieve something similar builder Design patterns
• ? Security operator
• Optional position parameters ： There is no need to write a bunch of overloaded functions , You can also provide default values

Method

• Underline names represent externally invisible
• The class name is not visible outside the beginning of the underscore
• Name the construction method
• Parameter initialization list

class Test {
    
  // Not visible from the outside 
  late int _x;

  Test(int a, int b);
  // Name the construction method 
  Test.a(int c) : this(c, 0);
  // Parameter initialization list 
  Test.fromMap(Map map) :_x = map["x"],_y = map["y"];
}

• Use new There is no difference between creating an object and a normal object
  Use const Create multiple objects , Parameters are the same , This object is a compiler constant object （ Constant constructor must be defined ）
• Factory construction method
  First, set the default constructor
  Then call the named constructor to return the constructor instance
  Factory methods must return instance objects
  static Method needs to display the declaration return object , Or no return

class Manager {
    
  // Factory construction method 
  factory Manager.get() {
    
    return new Manager();
  }
  Manager();
}

• get and set Method

  var x1 = new Xl();
  x1.x = 1;
  print(x1._x);

• operators overloading

class Xl {
    
  late int _x;
  int get x => _x;
  set x(int x) => _x = x;
  // operators overloading 
  Xl operator +(Xl other) {
    
    var xl = new Xl();
    xl._x = _x + other._x;
    return xl;
  }
}

• Each class can be viewed as an interface , It can be realized
• with Keywords can be mixed with other classes （ Although there is no official document stating that it is multi inheritance , I think it can be understood as multiple inheritance ）

class A {
    
  void a() {
    }
}

class B {
    
  void b() {
    }
}
//C  class   Mixed up A Classes and B class 
class C with A, B {
    
  void c() {
    }
}

class D = Object with A, B;

void main(){
    
  //C You can directly call the mixed class to break the law 
  var c = new C();
  c.a();
  c.b();
  c.c();
}

• Method if conflict The priority of the call ： First call C ,C No, Call again B ,A,with Post mixed classes Look backwards
• super You can call the functions of the parent class

If there is a problem , Welcome to point out