Section 10: Quizzler - Modularising & Organising Flutter Code

Collections

collections in dart that i can use are lists, sets and maps

Lists:

• to initialize a list I use literals to create and initialize lists.
• or I can use constructor to create lists.
• List class defines several methods for interacting with list such as adding, removing, counting and finding element inside list etc..
• create list:
  • Create an empty list String names = []; || var names = <String>[];
  • create list with list literals String names = ['Yazan','Any One '];
  • get the first element: names.first
  • get last item: names.last
  • add to list one item: names.add();
  • add to list multi items: names.addAll(['new name 1','new name 2']);
  • remove from list:

    int removedItem = names.indexOf('Yazan');
    names.removeAt();
    

• remove all items: fruit.clear();
• sort a list: names.sort((one, two)=> one.compareTo(b))
• Lists are parameterized types (generics), so I can specify the type that a list should contain:

// This list should contain only strings.
var fruits = <String>[];

fruits.add('apples');
fruits.add(5); // Error: 'int' can't be assigned to 'String'

Sets:

• A set in Dart is an unordered collection of unique items.
• Because a set is unordered, I can’t get a set’s items by index (position).
• create a list

  // Create an empty set of strings.
  var ingredients = <String>{};
  

• add new items toit. ```dart // Add new items to it. ingredients.addAll([‘gold’, ‘titanium’, ‘xenon’]); assert(ingredients.length == 3);

// add new single item ingredients.add(‘shit’);

// Adding a duplicate item has no effect. ingredients.add(‘gold’);

- remove item from set; `fruits.remove('apples')`
- check if item exist in set: `fruits.contains('gold')`.

###### Maps:
- A map, commonly known as a dictionary or hash, is an unordered collection of key-value pairs.
- Maps associate a key to some value for easy retrieval.
- Declare a map using a terse literal syntax:
```dart
// Maps often use strings as keys.
var hawaiianBeaches = {
  'Oahu': ['Waikiki', 'Kailua', 'Waimanalo'],
  'Big Island': ['Wailea Bay', 'Pololu Beach'],
  'Kauai': ['Hanalei', 'Poipu']
};

• declare with traditional constructor: ```dart // Maps can be built from a constructor. var searchTerms = Map();

// Maps are parameterized types; you can specify what // types the key and value should be. var nobleGases = Map<int, String>();

- to add, get, and set map items use the bracket syntax.
- Use remove() to remove a key and its value from a map.
```dart
var nobleGases = {54: 'xenon'};

// Retrieve a value with a key.
assert(nobleGases[54] == 'xenon');

// Check whether a map contains a key.
assert(nobleGases.containsKey(54));

// Remove a key and its value.
nobleGases.remove(54);

• To check whether a map contains a key; containsKey()

• Use isEmpty or isNotEmpty to check whether a list, set, or map has items:
• To apply a function to each item in a list, set, or map, you can use forEach():