Dart Basics - Collection Types

1. Definition of collection type

For collection types, Dart has the most commonly used three built-in: List / Set / Map.

Among them, Listit can be defined as follows:

// List定义// 1.使用类型推断定义
var letters = ['a', 'b', 'c', 'd'];
print('$letters ${
      
      letters.runtimeType}');
// 2.明确指定类型
List<int> numbers = [1, 2, 3, 4];print('$numbers ${
      
      numbers.runtimeType}');

Among them, setit can be defined as follows:

In fact, it's just a matter of []replacing it {}.
SetThe two Listbiggest differences are: Setit is unordered, and the elements are not repeated.

// Set的定义
// 1.使用类型推导定义
var lettersSet = {
    
    'a', 'b', 'c', 'd'};
print('$lettersSet ${
      
      lettersSet.runtimeType}');
// 2.明确指定类型
Set<int> numbersSet = {
    
    1, 2, 3, 4};
print('$numbersSet ${
      
      numbersSet.runtimeType}');

Finally, Mapthere is the dictionary type we often say, and its definition is as follows:

// Map的定义
// 1.使用类型推导定义
var infoMap1 = {
    
    'name': 'why', 'age': 18};
print('$infoMap1 ${
      
      infoMap1.runtimeType}');

// 2.明确指定类型
Map<String, Object> infoMap2 = {
    
    'height': 1.88, 'address': '北京市'};
print('$infoMap2 ${
      
      infoMap2.runtimeType}');

2. Common operations on collections

After understanding how these three collections are defined, let's look at some of the most basic public operations

The first category is the property of getting the length supported by all collections length:

// 获取集合的长度
print(letters.length);
print(lettersSet.length);
print(infoMap1.length);

The second category, is add/remove/include operations

And, Listfor the element is ordered, it also provides a method to delete the element at the specified index position

// 添加/删除/包含元素
numbers.add(5);
numbersSet.add(5);
print('$numbers $numbersSet');

numbers.remove(1);
numbersSet.remove(1);
print('$numbers $numbersSet');

print(numbers.contains(2));
print(numbersSet.contains(2));

// List根据index删除元素
numbers.removeAt(3);
print('$numbers');

The third category, yes Mapoperation

Since it has a key and a value, whether it is reading a value or operating, it must be clearly based on the key, or the value, or the key/value pair.

// Map的操作
// 1.根据key获取
valueprint(infoMap1['name']);

// 2.获取所有的entries
print('${
      
      infoMap1.entries} ${
      
      infoMap1.entries.runtimeType}');

// 3.获取所有的keys
print('${
      
      infoMap1.keys} ${
      
      infoMap1.keys.runtimeType}'); 

// 4.获取所有的values
print('${
      
      infoMap1.values} ${
      
      infoMap1.values.runtimeType}'); 

// 5.判断是否包含某个key或者value
print('${infoMap1.containsKey('age')} ${
      
      infoMap1.containsValue(18)}'); // true true


// 6.根据key删除元素
infoMap1.remove('age');print('${
      
      infoMap1}');

reference:

Teacher Coderwhy 's official account