{"id":637,"date":"2022-05-07T10:11:47","date_gmt":"2022-05-07T03:11:47","guid":{"rendered":"https:\/\/csharptutorial.net\/?page_id=637"},"modified":"2023-07-08T20:45:04","modified_gmt":"2023-07-08T13:45:04","slug":"csharp-list","status":"publish","type":"page","link":"https:\/\/www.csharptutorial.net\/csharp-collections\/csharp-list\/","title":{"rendered":"C# List<T>"},"content":{"rendered":"\n

Summary<\/strong>: in this tutorial, you’ll learn how to use the C# List<T><\/code> class to manipulate list elements effectively.<\/p>\n\n\n\n

Introduction to the C# List<T> class<\/h2>\n\n\n\n

The C# List<T><\/code> class allows you to manage a list of values of any type. The List<T><\/code> class represents a strongly typed list of objects that can be accessed by index.<\/p>\n\n\n\n

The T<\/code> inside the angle brackets specifies the type of elements in the list. For example, you can have a list of integers, strings, and objects.<\/p>\n\n\n\n

The List<T><\/code> belongs to the System.Collections.Generic<\/code> namespace.<\/p>\n\n\n\n

Creating a list<\/h2>\n\n\n\n

The following creates a new list of strings:<\/p>\n\n\n

List<string<\/span>> states = new<\/span> List<string<\/span>>();<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
And you can make it shorter by using the var<\/a><\/code> keyword:<\/p>\n\n\n
var<\/span> states = new<\/span> List<string<\/span>>();<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Adding an element to a list<\/h2>\n\n\n\n
To add an element to a list, you use the Add()<\/code> method. For example, the following uses the Add()<\/code> method to add three strings to the list:<\/p>\n\n\n
var<\/span> states = new<\/span> List<string<\/span>>();\n\nstates.Add(\"California\"<\/span>);\nstates.Add(\"Texas\"<\/span>);\nstates.Add(\"New York\"<\/span>);<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Iterating over the elements of a list<\/h2>\n\n\n\n
To iterate over the elements of a list, you use the foreach<\/a><\/code> statement. The foreach<\/code> statement assigns the current list element to a variable in each iteration from the first to the last element. <\/p>\n\n\n\n
For example, the following uses the foreach<\/code> statement to iterate over the elements of the states<\/code> list:<\/p>\n\n\n
var<\/span> states = new<\/span> List<string<\/span>>();\n\nstates.Add(\"California\"<\/span>);\nstates.Add(\"Texas\"<\/span>);\nstates.Add(\"New York\"<\/span>);\n\nforeach<\/span> (var<\/span> state in<\/span> states)\n{\n    Console.WriteLine(state);\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
California\nTexas\nNew York<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Using collection initializer<\/h2>\n\n\n\n
To simplify creating and populating a list, you can use a collection initializer. For example, the following creates a list and populates it with three elements:<\/p>\n\n\n
var<\/span> states = new<\/span> List<string<\/span>>() \n{\n    \"California\"<\/span>,\n    \"Texas\"<\/span>,\n    \"New York\"<\/span>\n};<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Checking if an element exists<\/h2>\n\n\n\n
To check if an element exists in a list, you use Contains()<\/code> method. The Contains()<\/code> method returns true<\/code> if an element exists in a list. Otherwise, it returns false<\/code>. <\/p>\n\n\n\n
For example:<\/p>\n\n\n
var<\/span> states = new<\/span> List<string<\/span>>()\n{\n    \"California\"<\/span>,\n    \"Texas\"<\/span>,\n    \"New York\"<\/span>\n};\n\nConsole.WriteLine(states.Contains(\"Texas\"<\/span>)); \/\/ True<\/span>\nConsole.WriteLine(states.Contains(\"Washington\"<\/span>)); \/\/ False<\/span><\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
In this example, the states<\/code> list contains \"Texas\"<\/code>. Therefore, the following method call returns true<\/code>:<\/p>\n\n\n
states.Contains(\"Texas\"<\/span>);<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Also, because the states<\/code> list doesn’t contain \"Washington\"<\/code>, the Contains()<\/code> method returns false<\/code>:<\/p>\n\n\n
states.Contains(\"Washington\"<\/span>);<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Accessing a list element using an index<\/h2>\n\n\n\n
The List<T><\/code> class allows you to access its elements using indices. The first element has an index of 0, the second element has an index of 1, and so on:<\/p>\n\n\n
listObject[index]<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
The following uses the for<\/a><\/code> statement to iterate over the list elements and convert them to uppercase:<\/p>\n\n\n
var<\/span> states = new<\/span> List<string<\/span>>()\n{\n    \"California\"<\/span>,\n    \"Texas\"<\/span>,\n    \"New York\"<\/span>\n};\n\nfor<\/span> (int<\/span> i = 0<\/span>; i < states.Count; i++)\n{\n    states[i] = states[i].ToUpper();\n    Console.WriteLine(states[i]);\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
CALIFORNIA\nTEXAS\nNEW YORK<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Inserting an element into a list<\/h2>\n\n\n\n
To insert an element into a list at a specified index, you use the Insert()<\/code> method. For example, the following inserts an element at the index 0 and another element at the index 1:<\/p>\n\n\n
var<\/span> states = new<\/span> List<string<\/span>>()\n{\n    \"California\"<\/span>,\n    \"Texas\"<\/span>,\n    \"New York\"<\/span>\n};\n\nstates.Insert(0<\/span>, \"Alaska\"<\/span>);\nstates.Insert(1<\/span>, \"Arizona\"<\/span>);\n\nforeach<\/span> (var<\/span> state in<\/span> states)\n{\n    Console.WriteLine(state);\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
Alaska\nArizona\nCalifornia\nTexas\nNew York<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Sort a list in ascending or descending order<\/h2>\n\n\n\n
To sort a list, you use the Sort()<\/code> method. The Sort()<\/code> method sorts the list elements using the default comparer. <\/p>\n\n\n\n
For example, the following uses the Sort()<\/code> method to sort a list of strings in ascending order:<\/p>\n\n\n
var<\/span> states = new<\/span> List<string<\/span>>()\n{\n    \"California\"<\/span>,\n    \"Texas\"<\/span>,\n    \"Arizona\"<\/span>,\n    \"New York\"<\/span>,\n    \"Alaska\"<\/span>\n};\n\nstates.Sort();\n\n\nforeach<\/span> (var<\/span> state in<\/span> states)\n{\n    Console.WriteLine(state);\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
Alaska\nArizona\nCalifornia\nNew York\nTexas<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
If you want to sort the list of strings in descending order, you can pass a comparer to the Sort()<\/code> method like this:<\/p>\n\n\n
var<\/span> states = new<\/span> List<string<\/span>>()\n{\n    \"California\"<\/span>,\n    \"Texas\"<\/span>,\n    \"Arizona\"<\/span>,\n    \"New York\"<\/span>,\n    \"Alaska\"<\/span>\n};\n\nstates.Sort((x, y) => y.CompareTo(x));\n\nforeach<\/span> (var<\/span> state in<\/span> states)\n{\n    Console.WriteLine(state);\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
Texas\nNew York\nCalifornia\nArizona\nAlaska<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Remove an element from a list<\/h2>\n\n\n\n
To remove an element from a list, you use the Remove()<\/code> method. The Remove()<\/code> method deletes the specified item from a list. <\/p>\n\n\n\n
If the item appears multiple times in a list, the Remove()<\/code> method removes the first occurrence of the item from the list.<\/p>\n\n\n\n
The following example uses the Remove()<\/code> method to remove “Texas” from the list:<\/p>\n\n\n
var<\/span> states = new<\/span> List<string<\/span>>()\n{\n    \"California\"<\/span>,\n    \"Texas\"<\/span>,\n    \"Arizona\"<\/span>,\n    \"New York\"<\/span>,\n    \"Alaska\"<\/span>\n};\n\nstates.Remove(\"Texas\"<\/span>);\n\nforeach<\/span> (var<\/span> state in<\/span> states)\n{\n    Console.WriteLine(state);\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
California\nArizona\nNew York\nAlaska<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Summary<\/h2>\n\n\n\n
    \n
  • Use the List<T><\/code> to manage a list of objects.<\/li>\n\n\n\n
  • Use the Add()<\/code> method to add an element to a list<\/li>\n\n\n\n
  • Use the Insert()<\/code> method to insert an element into a list at a specified index <\/li>\n\n\n\n
  • Use the Remove()<\/code> method to remove the first occurrence of an item from a list.<\/li>\n\n\n\n
  • Use the Sort()<\/code> method to sort elements of a list.<\/li>\n\n\n\n
  • Use the foreach<\/code> or for<\/code> statement to iterate over elements of a list.<\/li>\n\n\n\n
  • Use the Contains()<\/code> method to check if a list contains an element.<\/li>\n<\/ul>\n
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