The definition, function and usage of c# generic List

Definition: The List<T> class represents a strongly typed list of objects accessible through an index, providing methods for searching, sorting, and manipulating the list.

Function:
The most common use of generics is generic collections
When we create a list class, the data type of the list items may be int, string or other types. If the list class is processed in the same way,
there will be no The data type must be specified in advance and left to be specified when the list class is instantiated. It is equivalent to treating data types as parameters, which can maximize code reuse, protect type safety and improve performance.

General usage of List

Namespace to which it belongs: System.Collections.Generic
public class List<T>:IList<T>,Icollection<T>,IEnumerable<T>,IList,Icollection,Ienumerable
List<T&gt ; is the generic equivalent of the ArrayList class, which implements the IList<T> generic interface using an array whose size can be dynamically increased on demand

(1) Declare List<T>mlist = new List<T>( );

eg: string[] Arr = {"a","b","c"};
List<string> mlist = new List<string>(Arr);

(2) Add an element List.Add(T item)　 eg: mlist.Add("d");

(3) Add collection elements

eg: string[] Arr2 ={"f","g"."h"} ;

         mlist.AddRange(Arr2);

 

(4) Add an element at the index position Insert(int index,T item)

   eg: mlist.Insert(1,"p");

 

(5 ) Traverse the elements in the List

　foreach(T element in mlist) The type of T is the same as when mlist was declared

　　{

　　Console.WriteLine(element); {
                                Console .WriteLine(s);
       }

                                                                                                                                             . ;Delete the element with subscript index

eg: mlist.RemoveAt(0);

List.RemoveRange(int index,int count); Starting with index, delete count elements
eg: mlist.RemoveRange(3,2 );

(7) Determine whether an element is in the List

List.Contains(T item) Return true or false

eg:

if(mlist.Contains"("g"))
Console.WriteLine("g exists in the list");
else
mlist.Add("g");

(8) Sort the elements in the List List.Sort() The default is that each letter of the element is in ascending order

eg: mlist.Sort();

(9) Reverse the order of elements in List List.Reverse() can be used in conjunction with List.Sort()



(10) Clear List List.Clear()
eg: mlist.Clear();

(11) Obtain the number of elements in the List List.Count() and return the int value

eg: mlist.count();

Advanced List, powerful method

(1)List.FindAll method: Retrieve all elements that match the conditions defined by the specified predicate

class program

{

static void Main(stirng[] args)
                                                                                                                                                                                         stu.Name="arron";

List<student> students= new List<student>();

students.Add(stu);

students.Add(new student("candy"));

FindName myname = new FindName("arron");

Public class student
{
set;}
public student(){}
public override string ToString()
{
{0} return string. }
}

public class FindName

{
private string _name;
public FindName(string Name)
{ this._name=Name;}
public bool IsName(student s)
{ return (s.Name ==_name) ?true:false;}
}

(2) The List.Find method searches for elements that match the conditions defined by the specified predicate and returns the first matching element in the entire List

eg:

//Predicate is a delegate to the method. If the object passed to it matches the conditions defined by the delegate, the method returns true. The elements of the current List are passed to the Predicate delegate one by one, and are moved in the middle of the List, starting from the first elements and ends with the last element, processing stops when a match is found

The first method delegates to a lambda expression:
eg: string listFind = mlist.Find(name=>

{

if(name.length>3)
                   return true;

                                                                                                                                               if (name. Length>
The results of these two methods are the same

(3) List.FindLast method public T FindLast(Predicate<T> match);Determines whether each element in the List matches the conditions defined by the specified predicate. Usage is the same as List.Find.

(4) List.TrueForAll method: Determine whether each element in List matches the conditions defined by the specified predicate.

public bool TrueForAll(Predicate<T> match);

(5) List.Take(n): Get the first n rows and the return value is IEnumetable<T>, the type of T is the same as the type of List<T> ​​element in takeList: " + s);

                                 

           At this time, the elements stored in takeList are the first 5 elements in mList

(6) List.Where method: Retrieve all elements that match the conditions defined by the specified predicate. Similar to the List.FindAll method.

E.g.:

                           IEnumerable<string> whereList = mList.Where(name => 3)

                                                                                                                                                                                                    

​​​            foreach (string s in subList)                                                                                                                                            subList stores all elements with a length greater than 3

(7) List.RemoveAll method: Remove all elements that match the conditions defined by the specified predicate. ​​​​If (name.Length > 3)

                                                                                                                                        S}

else} {

return false;

}}});

Foreach (string s in mlist) {

console.writeline ("Element in mlist:" + s);

M}

At this time, Mlist stores elements that are greater than 3.

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