Flutterexperts

Introduction

Dart supports four types of collection with full-featured API. List, Set, Queue, Map are the four types of collection in Dart programming language. List, Set, Queue are iterable while Maps are not. Iterable collections can be changed i.e. their items can be modified, add, remove, can be accessed sequentially. The map doesn’t extend iterable.

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Iterable

Iterable is an extract class, it can’t de instantiate directly.

An Iterable of string and int

void main() {
  Iterable<int> var1 = [1,2,3,4];
  Iterable<String> var2 = ['a','b','c','d'];
}

The difference with List and Iterable is that that element in the list can be accessed with their index value using [] operator while in Iterable value can’t be accessed using [] operator.

void main() {
  Iterable<int> var1 = [1,2,3,4];
  Iterable<String> var2 = ['a','b','c','d'];
  print(var1[1]);
}

If we run the above program. We get the operator error.

Error compiling to JavaScript:
main.dart:4:13:
Error: The operator '[]' isn't defined for the class 'Iterable<int>'.
- 'Iterable' is from 'dart:core'.
print(var1[1]);
^
Error: Compilation failed.

Correct program:

void main() {
  Iterable<int> var1 = [1,2,3,4];
  Iterable<String> var2 = ['a','b','c','d'];
  print(var1.elementAt(1));
}

Output: 2

Using for loop to print element of iterable

void main() {
  Iterable<int> var1 = [1, 2, 3, 4];
  for (var element in var1) {
    print(element);
  }
}

Performing few operations:

void main() {
  Iterable<int> var1 = [1, 2, 3, 4];
  print(var1.first);
  print(var1.last);
  print(var1.length);
  print(var1.contains(1));
  print(var1.skip(1));
  print(var1.single);

}

OutPut:

1
4
4
true
(2, 3, 4)
Uncaught Error: Bad state: Too many elements

firstreturn the first element, last return the last element, length return the length of iterable, contains(1) return the element at position 1, skip(1) skip the element at position 1, single return the element if iterable has only one element. Throw this error if it has more than one element or empty Uncaught Error: Bad state: Too many elements .

List

A list is an array of elements arranged in an ordered sequence.

There are two types of List:

1. Fixed-Length List
2. Growable List

Fixed-Length List is a list that can’t be changed once initialized whereas the Growable list is dynamic in nature.

Fixed-length List

• Creating a Fixed-length List

void main() {
  List<String> list = List(5);
}

The indexing value start with 0 and end with listOfLength-1 . So for the list index values will be 0 to 4 .

• Here the list is empty, so let’s assign the value for each index:

void main() {
  List<String> list = List(5);
  list[0] = 'a';
  list[1] = 'b';
  list[2] = 'c';
  list[3] = 'd';
  list[4] = 'e';
}

• Printing the values:

print(list[1]);

• Updating the value:

void main() {
  List<String> list = List(5);
  list[0] = 'a';
  list[1] = 'b';
  list[2] = 'c';
  list[3] = 'd';
  list[4] = 'e';
  list[0] = 'm';
  print(list[0]);
}

Output:m .

Growable List

• Growable List example:

void main() {
  List<String> list = List();
}

• Inserting elements in List:

void main() {
  List<String> list = List();
  list.add('a');
  list.add('b');
  list.add('c');
}

• Updating element:

void main() {
  List<String> list = List();
  list.add('a');
  list.add('b');
  list.add('c');
  list[1]= 'm';
}

Set

A set is an unordered collection of values. We can’t get the values by their index values as they are unordered. Values in set are unique i.e. they can’t be repeated.

• Creating a Set using a constructor:

void main() {
  Set<int> set = Set();
}

• Creating a Set using List

void main() {
  List<int> list = [1, 2, 3, 4];
  Set<int> set = Set.from(list);
}

• Inserting elements in Set

void main() {
  List<int> list = [1, 2, 3, 4];
  Set<int> set = Set.from(list);
  set.add(5);
  set.add(6);
}

Maps

Maps is an unordered pair of key and values. The keys of the map must unique, values can be the same. Map is also called dictionary or hash .The size of a map is not fixed, we can add, delete edit the values of the map. The size of the map depends upon the number of elements in the map. The values in the map can only be accessed through the key name, not by the index values.

• Creating a map using constructor:

void main() {
  Map<String, int> map = Map();
}

Here we have created a map named map whose key type is String and value type is int .

• Adding a value and printing the map:

void main() {
  Map<String, int> map = Map();
  map['number'] = 1;
  print(map);
}

Output:{number: 1}

Accessing value by its key : print(map[‘number’]); .

Printing all keys and values of the map:

void main() {
  Map<String, int> map = Map();
  map['number1'] = 1;
  map['number2'] = 2;
  map['number3'] = 3;
  for (String keys in map.keys) {
    print(keys);
  }
  for (int values in map.values) {
    print(values);
  }
}

Output:

number1
number2
number3
1
2
3

Printing Key-Value pair:

map.forEach((key, value) {
  print("$key:$value");
});

OutPut:

number1:1
number2:2
number3:3

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