Dart language Learning

Hello World

void main() {
  print('Hello World!');
}

Comments

//this is a comment

Variables:

Dart is a strongly typed language. If we don’t specify the type it will be infered automatically from the intialization

var name = "Prince";

String name = "Prince";

If want a variable that can hold any type of values then we declare a dynamic variable in dart

dynamic name = "Prince";
name = 23;

An variable that is not initialized is null

int age;
print (age); //this prints "null"

Final vs Const

final is a runtime constant that can be set only once whereas const have to be initialized at the time of declartion. final can be intialized later

const pi = 3.1416;

double calculateArea(final r) {
  return pi * r * r;
}

void main() {
  var radius = 23;
  print(calculateArea(radius));

}

Notes: if we want to use const at class level we should be marked with static 	keyword

Example:

const key = "123acbd";
const double pi = 3.1416;
const baz = [];

We can also create constant value:

final me = const[];

Builtin Datatypes

  • num:

    includes basic operators (eg, + , / , *, -), bitwise operators and mathematical functions abs(), ceil(), floor(). There is two sub type of num:

    • int : 64bit

    • double: 64bit


  • String:

    sequence of UFT-16 code units. you can use both the double qoute and the single qoute. example:

      var s = "I love my `Android Studio`"; // single qoute inside double oute
  var s1 = 'I love my "Android Studio"'; //double qoute inside single qoute
  var s2 = "I love my \"Android Studio\""; //delimiter

    ###### Concate string

    we can concate adjacent string using the plus operator

      print ("My name is Prince Billy Graham. " +
      "My age is 23" +
      "I am a student");

    ###### Multiline String: We can also use tripple single qoute for multipline string:

      void main () {
print ('''My name is Prince Billy Graham. 
      My age is 23
      I am a student''');
  }

    ###### Raw string: In raw string special escape character doesn’t work.

      print(r"My name is \n \? Prince Billy Graham.");

    ###### String interpolation: we can use $ / ${} (for complex expressin) to insert equation aor variable to string.

      void main () {
    var name = "Prince Billy Graham Karmoker";
    print('My name is "$name"');
    print('My name is "${name.toUpperCase()}"');
    print('My age is ${10+23}');
  }

  • boolean : true / false


  • List:

    looks like javascript array literals.

    var cars = [
    'corola',
    'honda',
    if (person.class == "rich) 'BMW',
    for (brand in bicycle) brand.name,
];

    To get the length of a list we can use .length property of a list.

       cars,length //3

    ### Maps

       void main() {
        var cars = {
          "bmw": "X34",
          "tesla": "AX",
          "corola": "100",
        };
	  
        print(cars["tesla"]); //AX
  }

    ### Enums

      enum Color {
    red, 
    green, 
    blue
    }
	  
  void main() {
   print(Color); //Color
    print(Color.red); //Color.red
    print(Color.values);  //[Color.red, Color.green, Color.blue]
    print(Color.green.index); //1
  }

Control Statement

if / if - else / if - else if / if - else if - else

Nothing so new about it, just how you are use it in C++/javascript/typescript/kotlin

Functions

num addNumbers(int num1 , double num2) {
  return num1 + num2;
}

void main() {
  print(addNumbers(1,3.3));
}

A function with only one statement can also be written using fat arrow => symbol. The statement will also return if the function needs to return something.

void main() => runApp(MaterialApp())

Anonymous Function

single statement anonymous function:

() => "Hello World"     //<---- Also returns.

Multiple line anonymous function

() {
print("Hello World")
return true
}

Class

class Person {
  String name = "Max"; 
  int age =30;
}


void main() {
  var p1 =  Person();
  print(p1.age)
}]

Class with Constructor:

class Person {
  String name;
  int age;
  
  Person(String inputName, int age) {
	  name = inputName; //automatically reqonizes that 'name' is a class property
	  this.age = age;
	  //specifying that 'age' is the property of class using this
  }
}

void main() {
  var person = Person("Prince Billy Graham", 543);
  print(person);
}

We can also use named argument here. Named arguments are optional by default. [But while using flutter we can also make a named argument required by adding @required before the argument].

class Person {
  String name;
  int age;
  
  Person({String name @required int age) { //currently @required anotion is only a flutter feature.
	  this.name = name;
	  this.age = age;
  }
}

void main() {
  var person = Person(name:"Prince Billy Graham", age: 543);
  print(person);
}

A more shorter way of coding the constructing will be using this keyword directly at the constructor argument and no body at all (optional) . example (change only on the constructor)

Person({this.name, this.age});
Constructor Overloading

We can also overload a constructore like this example:

```dart
class Person {
  String name;
  int age;
  
  Person({this.name, this.age}) {
	  this.name = name;
	  this.age = age;
  }
	
 //constructor overloading
 Person.veryOld(this.name) {
	 this.age = 80;
 }
}


void main() {
	Person("Prince Billy Graham Karmoker");
	Person.veryOld("Steve");
}


Extending a class

We can also extend a class from a parent class using extends keyword. we can override parent class function inside subclass. But when overriding a parent class function inside subclass we should use @override anotion which is not mandatory but good practice

class MyApp extends StatelessWidget {  
	@override
	Widget build (BuildContext context) { //overriding parent class
		return MaterialApp(home: Text("Hello World"));
	}
}