byJeevan · July 14, 2021 14:59 · byJeevan · May 2, 2020 · byJeevan · Jan 9, 2021
diff --git a/Flutter Notes b/Flutter Notes
 --------------------------------------------------
 ##Flutter Notes 
 from byjeevan.blogspot.com
 --------------------------------------------------

 Course Res: https://github.com/londonappbrewery/Flutter-Course-Resources
 Flutter Cheetsheet : https://medium.com/flutter-community/flutter-layout-cheat-sheet-5363348d037e
 Dark Cheetsheet : https://dart.dev/codelabs/dart-cheatsheet

 🎯 Dart is Object Oriented Programming languages.

 Few frequently used Widgets : 
 **********************************************************
 🚀BoxDecoration widget -for- Background Image for Container
 choose AssetImage for Local or NetworkImage for remote.

 🚀'Visibility' widget usefull Hide and show buttons (ex. FlatButton) 

 🚀 'IconButton' widget helps to add simple AppBar Actions

 🚀 'SingleChildScrollView' with scrollDirections helps Row / Columns to make scrollable.

 🚀 'SizedBox(height: <eg. 20>)' gives space b/w Column childs

 🚀 Flat button comes with full set pack of 
    icon + text + action syntax:   FlatButton.icon(onPressed: null, icon: null, label: null)


 *************** Dart documentaiton notes ************* 17/04/2020
 1.
 Method return type if you not specify, then it will 'dynamic' type.

 void main() {
    print('hello ${returnsTest(1)}');
 }

 //below method can return int or string type.
 returnsTest(int flag) {
  
  if (flag == 1) {
     return 1;
  }
 
  return "na";
 }


 2.Important concepts

 Everything you can place in a variable is an object, and every object is an instance of a class. Even numbers, functions, and null are objects. All objects inherit from the Object class.

 Although Dart is strongly typed, type annotations are optional because Dart can infer types. In the code above, number is inferred to be of type int. When you want to explicitly say that no type is expected, use the special type dynamic.

 Dart supports generic types, like List<int> (a list of integers) or List<dynamic> (a list of objects of any type).

 Dart supports top-level functions (such as main()), as well as functions tied to a class or object (static and instance methods, respectively). You can also create functions within functions (nested or local functions).

 Similarly, Dart supports top-level variables, as well as variables tied to a class or object (static and instance variables). Instance variables are sometimes known as fields or properties.

 Unlike Java, Dart doesn’t have the keywords public, protected, and private. If an identifier starts with an underscore (_), it’s private to its library. For details, see Libraries and visibility.

 Identifiers can start with a letter or underscore (_), followed by any combination of those characters plus digits.

 Dart has both expressions (which have runtime values) and statements (which don’t). For example, the conditional expression condition ? expr1 : expr2 has a value of expr1 or expr2. Compare that to an if-else statement, which has no value. A statement often contains one or more expressions, but an expression can’t directly contain a statement.

 
 3. Function as parameter
 void main() {
  helloOne(hello);
 }

 void hello() {
  print("Hello World");
 }

 void helloOne(Function hello) {
  hello();
 }


 4.
 //'final' are Run-Time constant
    final List list = [1, 2, 3];

    list[2] = 4; //okey. Prints  [1, 2, 4]
 
    print(list);


 //'const' are Compile-Time constant
    const List list = [1, 2, 3];

    list[2] = 4; // error : Uncaught Error: Unsupported operation: indexed set
 
    print(list);


 5. List
 Array - Ordered collection of same object.
 We can use the spread operator (...) to insert all the elements of a list into another list

 List<String> brands = ['BMW', 'Tesla', 'TATA']
    To Add :
    brands.add('Honda')
    
    To find index:
    brands.indexOf('Tesla') //gives 1
    
    To insert item :
    brands.insert(2,'TOYOTA') //gives  ['BMW', 'Tesla', 'TOYOTA', 'TATA' , 'Honda']
    
    
    

 6. Set
 A set in Dart is an unordered collection of unique items.

   Set setOfUnique = {"one", "two", "three", "three", "four"};
   print(setOfUnique);

 7.Map 

 A map is an object that associates keys and values. Both keys and values can be any type of object. Each key occurs only once, but you can use the same value multiple times

 Map map = new Map();

 Map m = {"ID": "1234", "Name": "Sumit"};


 example : void main() {
   
   List l = ["one", "two", "three"];
  Map map = new Map();
  map["hello"] = "world";
  map["list"] = l;
  print(map);
 }


 9.Symbols
 A Symbol object represents an operator or identifier declared in a Dart program. You might never need to use symbols, but they’re invaluable for APIs that refer to identifiers by name, because minification changes identifier names but not identifier symbols.

 To get the symbol for an identifier, use a symbol literal, which is just # followed by the identifier:

 #radix
 #bar
 Symbol literals are compile-time constants.


 10.Functions
 => expr syntax (Arrow sytanx) is a shorthand for { return expr; }

 Example for Arrowed function:
 int add() => 5 + 2;

 is same as -
 int add() {
    return 5 + 2;
 }

 Optional parameters are mentioned inside {}
 Tip: Optional parameters can be either named or positional, but not both.

 11.

 Named parameters:


 Positional parameters:


 Required parameters:



 Default parameter values:
 Your function can use = to define default values for both named and positional parameters.
 /// Sets the [bold] and [hidden] flags ...
 void enableFlags({bool bold = false, bool hidden = false}) {...}

 // bold will be true; hidden will be false.
 enableFlags(bold: true);


 12. Exceptions :



 try {
  breedMoreLlamas();
 } on OutOfLlamasException {
  // A specific exception
  buyMoreLlamas();
 } on Exception catch (e) {
  // Anything else that is an exception
  print('Unknown exception: $e');
 } catch (e) {
  // No specified type, handles all
  print('Something really unknown: $e');
 }
 finally {
  // Always clean up, even if an exception is thrown.
  cleanLlamaStalls();
 }



 13.

 Callable classes
 To allow an instance of your Dart class to be called like a function, implement the call() method.


 class WannabeFunction {
  String call(String a, String b, String c) => '$a $b $c!';
 }

 var wf = WannabeFunction();
 var out = wf('Hi', 'there,', 'gang');

 main() => print(out);

 --------- FLUTTER SDK -------

 1. Minimal app code with 2 widgets tree as :
 (Material App Widget ---- > Text Widget)

 void main() {
  runApp(MaterialApp(home: Text("Hello World!"),),);
 }


 2. Use single ' for dart strings 
 Image widgets can be dartui or flutter widget.



 *** ShortCuts *****
 Hit [option]+ [Enter] to embed widgets options 
 hit [Control] + [j] to get Documentation dialog over any widget.

 To create stateless widget :-
 type 'stless' and hit enter.



 ****** Widgets *****

 - Single Child Widget : 
 Container, Center, SafeArea, Card (ps: add Padding widget), 
 Expanded (placed above Column to fillup space)

 - Multi Child widget 
 Row, Column, Stack

 OOPS !
 Encapsulation Private accessors 
 _ before object makes private variable


 class Car {
   int _bhpOfCar = 200; //Private to car class
   void drive(){
    print('Turn wheels');
   }
 }

 Inheritance:
 class ElectricCard extends Car {
 //gets all properites & methods from Car class.
 }

 Polymorphisms:
 class LevitatingCar extends Car {

    @override 
    void drive(){
        print('glide towards');
    }
 }


 Constructors:
 class Human {
    double height;
    
    //custom contructor
    Human({double startingHeight}) {
      height = startingHeight;
    }
    
    //-or-
     Human({double height}) {
      this.height = height;
    }
    
    //same as above constructor - non named parameters
    Human({this.height});    
    
    //Human() {} //Dart given default constructor
       
 }



 /**** Defining Global Constants ***/
 // Contants.dart file
 library constants;

 //Strings
 const String ERROR_MSG = 'Oops! Failed to add todo';

 //Colors
 const Color themeDarkColor = Color(0xff162447); // 0xff + 162447
 const Color themeLightColor = Color(0xff1f4068);
 const Color themePallet1Color = Color(0xff1b1b2f);
 const Color themePallet2Color = Color(0xffe43f5a);

 //Usage
 import 'constants.dart' as Constants;

 eg : color:themeDarkColor
 eg : Text(ERROR_MSG)


 *******
	--------------------------------------------------
	##Flutter Notes
	from byjeevan.blogspot.com
	--------------------------------------------------

	Course Res: https://github.com/londonappbrewery/Flutter-Course-Resources
	Flutter Cheetsheet : https://medium.com/flutter-community/flutter-layout-cheat-sheet-5363348d037e
	Dark Cheetsheet : https://dart.dev/codelabs/dart-cheatsheet

	🎯 Dart is Object Oriented Programming languages.

	Few frequently used Widgets :
	**********************************************************
	🚀BoxDecoration widget -for- Background Image for Container
	choose AssetImage for Local or NetworkImage for remote.

	🚀'Visibility' widget usefull Hide and show buttons (ex. FlatButton)

	🚀 'IconButton' widget helps to add simple AppBar Actions

	🚀 'SingleChildScrollView' with scrollDirections helps Row / Columns to make scrollable.

	🚀 'SizedBox(height: <eg. 20>)' gives space b/w Column childs

	🚀 Flat button comes with full set pack of
	icon + text + action syntax: FlatButton.icon(onPressed: null, icon: null, label: null)


	************* Dart documentaiton notes *********** 17/04/2020
	1.
	Method return type if you not specify, then it will 'dynamic' type.

	void main() {
	print('hello ${returnsTest(1)}');
	}

	//below method can return int or string type.
	returnsTest(int flag) {

	if (flag == 1) {
	return 1;
	}

	return "na";
	}


	2.Important concepts

	Everything you can place in a variable is an object, and every object is an instance of a class. Even numbers, functions, and null are objects. All objects inherit from the Object class.

	Although Dart is strongly typed, type annotations are optional because Dart can infer types. In the code above, number is inferred to be of type int. When you want to explicitly say that no type is expected, use the special type dynamic.

	Dart supports generic types, like List<int> (a list of integers) or List<dynamic> (a list of objects of any type).

	Dart supports top-level functions (such as main()), as well as functions tied to a class or object (static and instance methods, respectively). You can also create functions within functions (nested or local functions).

	Similarly, Dart supports top-level variables, as well as variables tied to a class or object (static and instance variables). Instance variables are sometimes known as fields or properties.

	Unlike Java, Dart doesn’t have the keywords public, protected, and private. If an identifier starts with an underscore (_), it’s private to its library. For details, see Libraries and visibility.

	Identifiers can start with a letter or underscore (_), followed by any combination of those characters plus digits.

	Dart has both expressions (which have runtime values) and statements (which don’t). For example, the conditional expression condition ? expr1 : expr2 has a value of expr1 or expr2. Compare that to an if-else statement, which has no value. A statement often contains one or more expressions, but an expression can’t directly contain a statement.


	3. Function as parameter
	void main() {
	helloOne(hello);
	}

	void hello() {
	print("Hello World");
	}

	void helloOne(Function hello) {
	hello();
	}


	4.
	//'final' are Run-Time constant
	final List list = [1, 2, 3];

	list[2] = 4; //okey. Prints [1, 2, 4]

	print(list);


	//'const' are Compile-Time constant
	const List list = [1, 2, 3];

	list[2] = 4; // error : Uncaught Error: Unsupported operation: indexed set

	print(list);


	5. List
	Array - Ordered collection of same object.
	We can use the spread operator (...) to insert all the elements of a list into another list

	List<String> brands = ['BMW', 'Tesla', 'TATA']
	To Add :
	brands.add('Honda')

	To find index:
	brands.indexOf('Tesla') //gives 1

	To insert item :
	brands.insert(2,'TOYOTA') //gives ['BMW', 'Tesla', 'TOYOTA', 'TATA' , 'Honda']




	6. Set
	A set in Dart is an unordered collection of unique items.

	Set setOfUnique = {"one", "two", "three", "three", "four"};
	print(setOfUnique);

	7.Map

	A map is an object that associates keys and values. Both keys and values can be any type of object. Each key occurs only once, but you can use the same value multiple times

	Map map = new Map();

	Map m = {"ID": "1234", "Name": "Sumit"};


	example : void main() {

	List l = ["one", "two", "three"];
	Map map = new Map();
	map["hello"] = "world";
	map["list"] = l;
	print(map);
	}


	9.Symbols
	A Symbol object represents an operator or identifier declared in a Dart program. You might never need to use symbols, but they’re invaluable for APIs that refer to identifiers by name, because minification changes identifier names but not identifier symbols.

	To get the symbol for an identifier, use a symbol literal, which is just # followed by the identifier:

	#radix
	#bar
	Symbol literals are compile-time constants.


	10.Functions
	=> expr syntax (Arrow sytanx) is a shorthand for { return expr; }

	Example for Arrowed function:
	int add() => 5 + 2;

	is same as -
	int add() {
	return 5 + 2;
	}

	Optional parameters are mentioned inside {}
	Tip: Optional parameters can be either named or positional, but not both.

	11.

	Named parameters:


	Positional parameters:


	Required parameters:



	Default parameter values:
	Your function can use = to define default values for both named and positional parameters.
	/// Sets the [bold] and [hidden] flags ...
	void enableFlags({bool bold = false, bool hidden = false}) {...}

	// bold will be true; hidden will be false.
	enableFlags(bold: true);


	12. Exceptions :



	try {
	breedMoreLlamas();
	} on OutOfLlamasException {
	// A specific exception
	buyMoreLlamas();
	} on Exception catch (e) {
	// Anything else that is an exception
	print('Unknown exception: $e');
	} catch (e) {
	// No specified type, handles all
	print('Something really unknown: $e');
	}
	finally {
	// Always clean up, even if an exception is thrown.
	cleanLlamaStalls();
	}



	13.

	Callable classes
	To allow an instance of your Dart class to be called like a function, implement the call() method.


	class WannabeFunction {
	String call(String a, String b, String c) => '$a $b $c!';
	}

	var wf = WannabeFunction();
	var out = wf('Hi', 'there,', 'gang');

	main() => print(out);

	--------- FLUTTER SDK -------

	1. Minimal app code with 2 widgets tree as :
	(Material App Widget ---- > Text Widget)

	void main() {
	runApp(MaterialApp(home: Text("Hello World!"),),);
	}


	2. Use single ' for dart strings
	Image widgets can be dartui or flutter widget.



	* ShortCuts ***
	Hit [option]+ [Enter] to embed widgets options
	hit [Control] + [j] to get Documentation dialog over any widget.

	To create stateless widget :-
	type 'stless' and hit enter.



	**** Widgets ***

	- Single Child Widget :
	Container, Center, SafeArea, Card (ps: add Padding widget),
	Expanded (placed above Column to fillup space)

	- Multi Child widget
	Row, Column, Stack

	OOPS !
	Encapsulation Private accessors
	_ before object makes private variable


	class Car {
	int _bhpOfCar = 200; //Private to car class
	void drive(){
	print('Turn wheels');
	}
	}

	Inheritance:
	class ElectricCard extends Car {
	//gets all properites & methods from Car class.
	}

	Polymorphisms:
	class LevitatingCar extends Car {

	@override
	void drive(){
	print('glide towards');
	}
	}


	Constructors:
	class Human {
	double height;

	//custom contructor
	Human({double startingHeight}) {
	height = startingHeight;
	}

	//-or-
	Human({double height}) {
	this.height = height;
	}

	//same as above constructor - non named parameters
	Human({this.height});

	//Human() {} //Dart given default constructor

	}



	/** Defining Global Constants */
	// Contants.dart file
	library constants;

	//Strings
	const String ERROR_MSG = 'Oops! Failed to add todo';

	//Colors
	const Color themeDarkColor = Color(0xff162447); // 0xff + 162447
	const Color themeLightColor = Color(0xff1f4068);
	const Color themePallet1Color = Color(0xff1b1b2f);
	const Color themePallet2Color = Color(0xffe43f5a);

	//Usage
	import 'constants.dart' as Constants;

	eg : color:themeDarkColor
	eg : Text(ERROR_MSG)


	*******