[fluent] dart data type list set type (define set | initialize | generic usage | add elements after initialization | set generation function | set traversal)

I . Define the collection and initialize

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Define and initialize List aggregate : Define a collection , And initialize the set ;

① Set element data type : Collection element types are generic , Any data type can be accepted ;

② Set element types : If no generics are specified , Collection can hold different types of elements ,

③ give an example : In a collection that does not specify a generic type int , double , String , bool Element of type ;

④ List Set initialization add elements : Use [] Initialize collection elements ;

List list = [1, 1.0, ' character string ' , true];// Use  print  You can print collections directly // Print set  list : [1, 1.0,  character string , true]print(" Print set  list : $list");

II . Collection generic usage

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Set generics :

① Specifying generics : If the collection is declared , Generic specified , Then only elements of this generic type can be stored ;

( Appoint int Collection of generic types , Only store int Element of type )

② Assignment limit : Generic different List Set variables cannot be assigned to each other ;

List<int> list_int = [1 , 2, 3];// Print set  list1 : [1, true]print(" Print set  list_int : $list_int");

III . Set add elements

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1 . Set elements add : In addition to adding elements during initialization , You can also call the add ( ) and addAll ( ) Additive elements ;

2 . Add a single element : adopt add ( ) Method Add a single element ;

List list1 = [];list1.add(1);list1.add(true);// Print set  list1 : [1, true]print(" Print set  list1 : $list1");

3 . Add multiple elements : adopt addAll ( ) Method Add multiple elements ;

List list = [1, 1.0, ' character string ' , true];  List list2 = [];list2.addAll(list);// Print set  list2 : [1, 1.0,  character string , true]print(" Print set  list2 : $list2");

IV . Set generation function

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1 . Set generation function : Call collection List Of generate ( ) Method , You can call the generation function to generate the elements generated according to the requirements ;

2 . generate ( ) The function prototype :

① int length Parameters :List Number of collection elements ;

② E generator(int index) Parameters : Callback function for generating elements , among index Is the element index value ;

  /** * Generates a list of values. * * Creates a list with [length] positions and fills it with values created by * calling [generator] for each index in the range `0` .. `length - 1` * in increasing order. * * new List<int>.generate(3, (int index) => index * index); // [0, 1, 4] * * The created list is fixed-length unless [growable] is true. */  factory List.generate(int length, E generator(int index),      { 
    bool growable = true}) { 
        List<E> result;    if (growable) { 
          result = <E>[]..length = length;    } else { 
          result = List<E>(length);    }    for (int i = 0; i < length; i++) { 
          result[i] = generator(i);    }    return result;  }

3 . Code example :

// The generating function of the set // int length  Parameters  :  The length of the set // E generator(int index) :  Callback function of collection  ,  Call this function to get the  index  The element of location List list_generate = List.generate(3, ( index ) => index * 3);// Print set  list_generate : [0, 3, 6]print(" Print set  list_generate : $list_generate");

V . A collection of traverse

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1 . adopt With cyclic conditions Ordinary for Loop traversal :

// 1 .  The way  1 :  Access the collection by subscript for(int i = 0; i < list_generate.length; i ++){ 
      print(list_generate[i]);}

2 . adopt var obj in list_generate Styling for Loop traversal :

// 2 .  The way  2 :  adopt  var obj in list_generate  Get the elements in the collection for( var obj in list_generate ){ 
      print(obj);}

3 . adopt For Each Loop traversal :

// 3 .  The way  3 : For Each  loop list_generate.forEach( ( element ){ 
      print(element);} );

VI . Set example code

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1 . Sample code :

import 'package:flutter/material.dart';class DartType_List extends StatefulWidget { 
      @override  _DartType_ListState createState() => _DartType_ListState();}class _DartType_ListState extends State<DartType_List> { 
      @override  Widget build(BuildContext context) { 
        listDemo();    return Container(child: Text('List  data type '));  }  /** * List  Example set  */  listDemo(){ 
        // I .  Define a collection     // Define a collection  ,  And initialize the set     //  Set element data type  :  The collection element type is generic  ,  Any data type can be accepted     //  Set element types  :  If no generics are specified  ,  Collection can hold different types of elements     //  For example, it is stored in a collection without specifying a generic type  int , double , String , bool  Element of type     //  Initialize add element  :  Use  []  Initialize collection elements     List list = [1, 1.0, ' character string ' , true];    // Use  print  You can print collections directly     // Print set  list : [1, 1.0,  character string , true]    print(" Print set  list : $list");    // II .  Collection generic usage     // If the collection is declared  ,  Generic specified  ,  Then only elements of this generic type can be stored     //  Such as  :  Appoint  int  Collection of generic types  ,  Only store  int  Element of type     //  Generic different  List  Set variables cannot be assigned to each other     //  Don't put the above  list  Set is assigned to   The  list_int    List<int> list_int = [1 , 2, 3];    // Print set  list1 : [1, true]    print(" Print set  list_int : $list_int");    // III .  Add elements after initialization     // In addition to adding elements during initialization     //  You can also call the  add ( )  and  addAll ( )  Additive elements     //  adopt  add ( )  Method   Add a single element     List list1 = [];    list1.add(1);    list1.add(true);    // Print set  list1 : [1, true]    print(" Print set  list1 : $list1");    //  adopt  addAll ( )  Method   Add multiple elements     List list2 = [];    list2.addAll(list);    // Print set  list2 : [1, 1.0,  character string , true]    print(" Print set  list2 : $list2");    // IV .  The generating function of the set     // The generating function of the set     // int length  Parameters  :  The length of the set     // E generator(int index) :  Callback function of collection  ,  Call this function to get the  index  The element of location     List list_generate = List.generate(3, ( index ) => index * 3);    // Print set  list_generate : [0, 3, 6]    print(" Print set  list_generate : $list_generate");    // V .  A collection of traverse     // 1 .  The way  1 :  Access the collection by subscript     for(int i = 0; i < list_generate.length; i ++){ 
          print(list_generate[i]);    }    // 2 .  The way  2 :  adopt  var obj in list_generate  Get the elements in the collection     for( var obj in list_generate ){ 
          print(obj);    }    // 3 .  The way  3 : For Each  loop     list_generate.forEach( ( element ){ 
          print(element);    } );      }}

2 . Execution results :

 Print set  list : [1, 1.0,  character string , true] Print set  list_int : [1, 2, 3] Print set  list1 : [1, true] Print set  list2 : [1, 1.0,  character string , true] Print set  list_generate : [0, 3, 6]036036036