1, Basic chapter

1.1 advantages of dart language

Advantages of Dart language

1. AOT compilation and JIT compilation are supported

2. Dart is a single thread and preemption is not allowed.

TODO: learn more about AOT and JIT

1.2 basic syntax of dart language

Variable declaration

1. You can define variables through var and support closures

2. Dart is a strongly typed language, which automatically deduces the type, and the variable type cannot be changed.

3. Variables that are not initialized will be given a default value of null

4. Constant declaration: const, final. The difference is

• const compile time constant must be initialized at declaration time, and the initialization value must be a determined value without calculation.
• final runtime constant, initialization at declaration / constructor initialization, and the value can be calculated dynamically.

Basic type

number,String,bool,list,map,set

number

• The number type only has Int and double.

num x = 1; // x can have both int and double values
x += 2.5;

• String to number: int.parse(), double.parse()

• Number to string: intNum.toString(), doublenum. Tostrinasfixed (n) keep N decimal places.

// String -> int
var one = int.parse('1');
assert(one == 1);

// String -> double
var onePointOne = double.parse('1.1');
assert(onePointOne == 1.1);

// int -> String
String oneAsString = 1.toString();
assert(oneAsString == '1');

// double -> String
String piAsString = 3.14159.toStringAsFixed(2);
assert(piAsString == '3.14');

Strings

• Use variables in strings, wrapped with ${} / $variables

var s = 'string interpolation';

assert('Dart has $s, which is very handy.' ==
    'Dart has string interpolation, '
        'which is very handy.');
assert('That deserves all caps. '
        '${s.toUpperCase()} is very handy!' ==
    'That deserves all caps. '
        'STRING INTERPOLATION is very handy!');

• '...' ','... ', indicates a multiline string

var s1 = '''
You can create
multi-line strings like this one.
''';

var s2 = """This is also a
multi-line string.""";

• r '...', r '...' means "raw" string TODO

Bool value

Dart is a strong bool type check. It is considered true only if the value of bool type is true

List list

Create, add, delete, query and sort

• Create list

  1,new List

  2. Simple List

  3. Set if and set for

// 1,new List
var vegetables = new List();
// 2. Simply use List to assign values
var fruits = ['apples', 'oranges'];

var constantList = const [1, 2, 3];// Constant list
// constantList[1] = 1; // This line will cause an error.

// 3. Set if
var nav = [
  'Home',
  'Furniture',
  'Plants',
  if (promoActive) 'Outlet'
];

// 3. Set for
var listOfInts = [1, 2, 3];
var listOfStrings = [
  '#0',
  for (var i in listOfInts) '#$i'
];
assert(listOfStrings[1] == '#1')

• Add element

Dart 2.3 adds the extension operator... And the expansion operator?

var list = [1, 2, 3];
var list2 = [0, ...list];
assert(list2.length == 4);

var list;
var list2 = [0, ...?list];
assert(list2.length == 1);

Methods of adding elements: add() adds one element and addAll() adds multiple elements

// Add element
fruits.add('kiwis');

// Add multiple elements
fruits.addAll(['grapes', 'bananas']);

• Delete element

// Delete the element at the specified position and return the deleted element
fruits.removeAt(index);

// If the specified element is deleted, true is returned for success and false is returned for failure
fruits.remove('apples');

// Delete the last element and return the deleted element
fruits.removeLast();

// Delete the specified range element, including header but not tail. null will be returned if successful
fruits.removeRange(start,end);

// Delete the element of the specified condition and return null successfully
fruits.removeWhere((item) => item.length >6)；

// Delete all elements
fruits.clear();

• Query element

// Get the first element
fruits.first;

// Gets the last element of the element
fruits.last;

// Find the index number of an element
assert(fruits.indexOf('apples') == 0);

• sort

// sort() sorts the elements and passes in a function as a parameter. Return < 0 means from small to large, and > 0 means from large to small
fruits.sort((a, b) => a.compareTo(b));

Set

Unique unordered set.

• Create Set

// 1. Simple assignment
var halogens = {'fluorine', 'chlorine', 'bromine', 'iodine', 'astatine'};
//Note that var names = {}; This creates a map, not a set!
// 2,
var names = <String>{};
Set<String> names = {};

• Add elements add and addAll to Set
• Judge whether the Set contains an element: set.contains(item)

//Include
_saved.contains(pair);

//remove
_saved.remove(pair);

Map

• Create Map

// Declaration of Map
var hawaiianBeaches = {
    'oahu' : ['waikiki', 'kailua', 'waimanalo'],
    'big island' : ['wailea bay', 'pololu beach'],
    'kauai' : ['hanalei', 'poipu']
};
var searchTerms = new Map();

// Specifies the parameter type of the key value pair
var nobleGases = new Map<int, String>();

// For the assignment of Map, the Key is in brackets, which is not an array
nobleGase[54] = 'dart';

//Key value pairs in the Map are unique
//Unlike Set, if the Key entered for the second time exists, the Value will overwrite the previous data
nobleGases[54] = 'xenon';
assert(nobleGases[54] == 'xenon');

// Retrieve whether the Map contains a Key
assert(nobleGases.containsKey(54));

//Delete a key value pair
nobleGases.remove(54);
assert(!nobleGases.containsKey(54));

function

Return value type before function

bool isNoble ( int atomicNumber ) { return _nobleGases [ atomicNumber ] != null ; } 

isNoble ( atomicNumber ) { return _nobleGases [ atomicNumber ] != null ; } 

bool isNoble ( int atomicNumber ) => _nobleGases [ atomicNumber ] != null ;   

parameter

Function parameters can be followed by named parameters and optional positional parameters (but not both).

Named parameters

Function parameters are named. When passing parameters, you need to specify which data to pass to which parameters.

// Function definition
void enableFlags({bool bold,required bool hidden}) {...}
// function call
enableFlags(bold: true, hidden: false);

required must pass a parameter

Optional location parameters

Optional location parameter. Use [] to wrap the parameter. This location parameter can not be transferred.

String say(String from, String msg, [String? device]) {
  var result = '$from says $msg';
  if (device != null) {
    result = '$result with a $device';
  }
  return result;
}

Parameter defaults

void enableFlags({bool bold = false, bool hidden = false}) {...}

Conditional judgment and circulation

• if...else
• for
• while do-while
• break continue
• switch... Case if there is an expression after the case but no break, an exception will be thrown
• assert (valid only in checked mode). If the condition is false, an exception is thrown

if - else

The judgment value must be true or false, and cannot be anything else!

for loop

var message = StringBuffer('Dart is fun');
for (var i = 0; i < 5; i++) {
  message.write('!');
}

var collection = [1, 2, 3];
collection.forEach(print); // 1 2 3

asynchronous

Future,async/await

Future

Similar to Promise, execute then successfully, catchrror if failed, and whenComplete anyway

void main() {
  Future.delayed(new Duration(seconds: 1), () {
    return "666";
  }).then((data) {
    // Execute after success
    print(data);
  }).catchError((e) {
    // Execute after failure
    print("error");
  }).whenComplete(() {
    // It will be executed regardless of success or failure
    print("complete");
  });
}

async/await

Add async after function ()

void main() async{
  print(await getString());
}

getString() {
  return Future.delayed(new Duration(seconds: 1), () {
    return "666";
  });
}