Introduction

A List is one of the generic collection classes in the "System.Collection.Generic" namespace. There are several generic collection classes in the System.Collection.Generic namespace that includes the following:

  1. Dictionary
  2. List
  3. Stack
  4. Queue

A List class can be used to create a collection of any type. For example, we can create a list of Integers, strings and even any complex types.

Why use a List

  1. Unlike arrays, a List can grow in size automatically. In other words, a list can be re-sized dynamically but arrays cannot.
  2. List is a generic type.
  3. The List class also provides methods to search, sort and manipulate lists.

Example 1 - Using Array

I am taking an example to store data in an array and see what the problem is in storing the data in the array.

using System;  
using System.Collections.Generic;  
  
namespace List_Methods_Properties  
{  
    class Program  
    {  
        static void Main(string[] args)  
        {  
            customer customer1 = new customer()  
            {  
                EmpID = 1,  
                EmpName = "Sourabh",  
                EmpSalary = 50000  
            };  
            customer customer2 = new customer()  
            {  
                EmpID = 2,  
                EmpName = "Shaili",  
                EmpSalary = 60000  
            };  
            customer customer3 = new customer()  
            {  
                EmpID = 3,  
                EmpName = "Saloni",  
                EmpSalary = 55000  
            };  
            //Customer array
            customer[] customers = new customer[2];  
            customers[0] = customer1;  
            customers[1] = customer2;  
  
            //here I am adding one more cutomer to customers array and building the programs  
            customers[2] = customer3;  
        }  
    }  
    class customer  
    {  
        public int EmpID { get; set; }  
        public string EmpName { get; set; }  
        public int EmpSalary { get; set; }  
  
    }  
}

In the example above, I have created one class named "customer" and In the main method I have created an array named customers with a size of two. When I build this program (using CTRL+SHIFT+B) then I will get output like built successfully but when I run this program then I get the error:

When I run this program then at run time I will get the exception index was out of the bound of the array.

So now we use List

A list is a generic data type that can hold any type of data that may be integer, float, string or may be complex type. To create a list we have 3 types of constructors.

List<Type> Customers = new List<Type>();//default constructor  
List<Type> Customers = new List<Type>(int capacity);//with spacific capacity
List<Type> Customers = new List(IEnumerable<Type> collection);//with spacific collection  

Example 2 - Using List

using System;  
using System.Collections.Generic;  
  
namespace List_Methods_Properties  
{  
    class Program  
    {  
        static void Main(string[] args)  
        {  
            customer customer1 = new customer()  
            {  
                EmpID = 1,  
                EmpName = "Sourabh",  
                EmpSalary = 50000  
            };  
            customer customer2 = new customer()  
            {  
                EmpID = 2,  
                EmpName = "Shaili",  
                EmpSalary = 60000  
            };  
            customer customer3 = new customer()  
            {  
                EmpID = 3,  
                EmpName = "Saloni",  
                EmpSalary = 55000  
            };  
  
            //using list  
            // Creating List with initial capacity 2  
            List<customer> Customers = new List<customer>(2);  
            Customers.Add(customer1);  // Here Add Method is used to add the item to the list
            Customers.Add(customer2);  
  
            //adding one more customer wheather capacity is 2 only  
            Customers.Add(customer3);  
        }  
    }  
    class customer  
    {  
        public int EmpID { get; set; }  
        public string EmpName { get; set; }  
        public int EmpSalary { get; set; }  
  
    }  
}

Output

In the preceding example we are adding 3 items to the list wereas the capacity is only two so it proves that a List can be automatically re-sized.

Add Method

Add method is used to add the items to the list.

How to access items from the C# List

To add the item to the list we use an index number to access it.

// <List Item>[index number]  

Code

using System;    
using System.Collections.Generic;    
    
namespace List_Methods_Properties    
{    
    class Program    
    {    
        static void Main(string[] args)    
        {    
            customer customer1 = new customer()    
            {    
                EmpID = 1,    
                EmpName = "Sourabh",    
                EmpSalary = 50000    
            };    
            customer customer2 = new customer()    
            {    
                EmpID = 2,    
                EmpName = "Shaili",    
                EmpSalary = 60000    
            };    
            customer customer3 = new customer()    
            {    
                EmpID = 3,    
                EmpName = "Saloni",    
                EmpSalary = 55000    
            };    
    
            //using list    
            // Creating List with initial capacity 2    
            List<customer> Customers = new List<customer>(2);    
            Customers.Add(customer1);    
            Customers.Add(customer2);    
            Customers.Add(customer3);    
    
            //Accessing Item from the List    
    
            customer c1 = Customers[0];    
            Console.WriteLine("ID={0}, Name={1}, Salary={2}",c1.EmpID,c1.EmpName,c1.EmpSalary);    
    
            customer c2 = Customers[1];    
            Console.WriteLine("ID={0}, Name={1}, Salary={2}", c2.EmpID, c2.EmpName, c2.EmpSalary);    
    
            customer c3 = Customers[2];    
            Console.WriteLine("ID={0}, Name={1}, Salary={2}", c3.EmpID, c3.EmpName, c3.EmpSalary);    
        }    
    }    
    class customer    
    {    
        public int EmpID { get; set; }    
        public string EmpName { get; set; }    
        public int EmpSalary { get; set; }    
    
    }    
}

How to access all the items of the list using foreach loop,

using System;  
using System.Collections.Generic;  
  
namespace List_Methods_Properties  
{  
    class Program  
    {  
        static void Main(string[] args)  
        {  
            customer customer1 = new customer()  
            {  
                EmpID = 1,  
                EmpName = "Sourabh",  
                EmpSalary = 50000  
            };  
            customer customer2 = new customer()  
            {  
                EmpID = 2,  
                EmpName = "Shaili",  
                EmpSalary = 60000  
            };  
            customer customer3 = new customer()  
            {  
                EmpID = 3,  
                EmpName = "Saloni",  
                EmpSalary = 55000  
            };  
  
            //using list  
            // Creating List with initial capacity 2  
            List<customer> Customers = new List<customer>(2);  
            Customers.Add(customer1);  
            Customers.Add(customer2);  
            Customers.Add(customer3);  
  
            //Accessing Item from the List using for loop  
  
            foreach (customer c in Customers)  
            {  
                Console.WriteLine("ID={0}, Name={1}, Salary={2}", c.EmpID, c.EmpName, c.EmpSalary);  
            }  
        }  
    }  
    class customer  
    {  
        public int EmpID { get; set; }  
        public string EmpName { get; set; }  
        public int EmpSalary { get; set; }  
    }  
}

Output

Note

You can also use for or while loop to access all the items.

Different Properties of a C# List

  1. Count: This property is the number of items of the List.
  2. Capacity: This property is the capacity of the List. By default the capacity is 0, then starts with 4, 8, 16, 32.....
using System;  
using System.Collections.Generic;  
  
namespace List_Methods_Properties  
{  
    class Program  
    {  
        static void Main(string[] args)  
        {  
            List<string> Names = new List<string>();  
            Names.Add("Sourabh");  
            Names.Add("Shaili");  
            Names.Add("Saloni");  
            Console.WriteLine("Number of Items in the List is:" + Names.Count);  
            Console.WriteLine("Capacity of the List is:" + Names.Capacity);  
        }  
    }  
}  

Output

Different Methods of a C# List

  1. Contains: This method determines whether or not an element is in the List, if the element is present in the List then this method returns "True" else "False".
  2. Insert: This method is used to insert an element at a specific index.
  3. Remove: This method removes the first occurrence of the specific object from the list.
  4. RemoveAll: This method removes all the elements that matches the condition.
  5. RemoveAt: This method remove the element from the specified index.
  6. Clear: Removes all the element from the list.
  7. Sort: This method is used sort the List
  8. Reverse: This method reverses the order of the elements in the entire List.
  9. TrimExcess: This method sets the capacity to the actual number of elements in the list.

Example

using System;  
using System.Collections.Generic;  
  
namespace List_Methods_Properties  
{  
    class Program  
    {  
        static void Main(string[] args)  
        {  
            List<string> Names = new List<string>();  
            Names.Add("Sourabh");  
            Names.Add("Shaili");  
            Names.Add("Saloni");  
            Names.Add("Ankit");  
            Names.Add("Bill");  
            Names.Add("Dinesh");  
            Names.Add("Mahesh Chand");  
            Names.Add("DJ");  
            Names.Add("Rajesh");  
            Names.Add("Rajesh");  
            Names.Add("Rajesh");  
            //Contains: This method determines that weather the element is in List or not,   
            //If element is present in List then this method returns "True" else return "False".   
            Console.WriteLine(Names.Contains("Sourabh\n"));  
  
            //accessing all the element from the list  
            foreach (string Name in Names)  
            {  
                Console.WriteLine(Name);  
            }  
              
            //Insert: This method is used to insert an element in particular index.  
            Names.Insert(5, "Rajesh");  
  
            Console.WriteLine("\n\nAfter Inserting Rajesh at 5th index");  
            foreach (string Name in Names)  
            {  
                Console.WriteLine(Name);  
            }  
  
            //Sort: Sorts the List  
            Names.Sort();  
            Console.WriteLine("\n\nSorting in List");  
            foreach (string Name in Names)  
            {  
                Console.WriteLine(Name);  
            }  
  
            //Reverse: Reverse the order of the element of List  
            Names.Reverse();  
            Console.WriteLine("\n\nReverse Elements of List");  
            foreach (string Name in Names)  
            {  
                Console.WriteLine(Name);  
            }  
  
            //Remove: Removes the elements from the list              
            Names.Remove("Rajesh");  
            Console.WriteLine("\n\nRemove Element from the List using Remove Method");  
            foreach (string Name in Names)  
            {  
                Console.WriteLine(Name);  
            }  
  
            //RemoveAt:Remove the elements from the list at the specific index  
            Names.RemoveAt(7);  
            Console.WriteLine("\n\nRemove Element from the List using RemoveAt Method");  
            foreach (string Name in Names)  
            {  
                Console.WriteLine(Name);  
            }  
  
            //nTrimExcess:Sets the capacity to the actual number of elements in the List  
            Names.TrimExcess();  
            Console.WriteLine("\n\nTrimExcess Method");  
            Console.WriteLine("Capacity: {0}", Names.Capacity);  
            Console.WriteLine("Count: {0}", Names.Count);  
  
            //Clear:Removes all elements from the List  
            Names.Clear();  
            Console.WriteLine("\n\nClear Method");  
            Console.WriteLine("Capacity: {0}", Names.Capacity);  
            Console.WriteLine("Count: {0}", Names.Count);  
            Console.ReadKey();  
        }  
    }  
}

Output

In this article, we saw some use cases of List<T>.

Further readings

Basic Introduction to List In C# and .NET Core