In this article, we’ll look at how to update an item in a List in C#, using a simple library management system as an example. We’ll explore the intricacies of this common operation and learn how to manipulate lists in our C# applications effectively.<\/p>\n
Let’s start.<\/p>\n
In the world of C#, one of the most commonly used data structures is There are several methods for finding elements in a Let’s start creating a book model:<\/p>\n Let’s continue creating the library class:<\/p>\n In our Library class, there are two main parts. First, our constructor\u00a0seeds the publicly accessible list By default, C# offers methods to update items in a list. Let’s have a look at these methods.<\/p>\n The Let’s use an index first:<\/p>\n The As already announced, we still have to make changes to our book class for the In our case, two So let’s update our Book class:<\/p>\n Here, we override the The Let’s create a checkout method using the In our Similarly, Let’s create a method similar to our previous examples, but now using the In our In C#, we can also use the Language Integrated Query (LINQ)<\/a> to find and update an element in a list. This approach is more flexible and more efficient than conventional methods.<\/p>\nList<T><\/code>. This versatile collection class provides the ability to store and manipulate a series of elements of a specific type<\/strong>, labeled T<\/code>. It’s similar to an array but with more features. It dynamically adjusts its size as we add or remove elements, and it has several useful methods for sorting, searching, and editing data.<\/p>\nList<\/code> class, please check out our article C# Intermediate \u2013 Generic List and Dictionary<\/a>.<\/div>\nList Set up for Finding and Updating Item<\/h2>\n
List<\/code>, each with its own strengths and ideal use cases. We will set up a small library program and go through the different methods.<\/p>\npublic class Book(string title, string author, string isbn, bool isCheckedOut)\r\n{\r\n public string Title { get; set; } = title;\r\n\r\n public string Author { get; set; } = author;\r\n\r\n public string ISBN { get; set; } = isbn;\r\n\r\n public bool IsCheckedOut { get; set; } = isCheckedOut;\r\n}<\/pre>\npublic class Library\r\n{\r\n public List<Book> Books { get; set; }\r\n\r\n public Library()\r\n {\r\n Books =\r\n [\r\n new(\"Harry Potter and the Philosopher's Stone\", \"J.K. Rowling\", \"978-0439708180\", false),\r\n new(\"Harry Potter and the Chamber of Secrets\", \"J.K. Rowling\", \"978-0439064873\", false),\r\n new(\"Harry Potter and the Goblet of Fire\", \"J.K. Rowling\", \"978-0439139601\", false),\r\n new(\"Harry Potter and the Order of the Phoenix\", \"J.K. Rowling\", \"978-0439358071\", false),\r\n new(\"Harry Potter and the Half-Blood Prince\", \"J.K. Rowling\", \"978-0439785969\", false),\r\n ];\r\n }\r\n\r\n public Book AddBook(string title, string author, string isbn, bool isCheckedOut)\r\n {\r\n var book = new Book(title, author,\u00a0isbn, isCheckedOut);\r\n Books.Add(book);\r\n\r\n return book;\r\n }\r\n}<\/pre>\nBooks<\/code> with 5 newly created book objects. Secondly, our AddBook()<\/code> method creates a new book object using the specified parameter values for the author, title,\u00a0 ISBN, and checkout status. The newly created book is then added to our Books<\/code> list.<\/p>\nFind and Update an Item in a List Using Built-In Methods<\/span><\/span><\/h2>\n
Update List Item With IndexOf() Method<\/h3>\n
IndexOf()<\/code> method is simple and efficient. It returns the zero-based index of the first occurrence of an element in the list.<\/strong> However, it uses the standard equality comparator, which we have to override to match our book comparison case.<\/p>\npublic void CheckoutBookUsingIndexOf(Book book)\r\n{\r\n var index = Books.IndexOf(book);\r\n if (index > -1)\r\n {\r\n Books[index].IsCheckedOut = true;\r\n }\r\n}<\/pre>\nIndexOf()<\/code> method we call in our CheckoutBookUsingIndexOf()<\/code> method, uses our provided book object to check the Books<\/code> list from our Library<\/code> class. In return, we receive the index of the book<\/code> object in the Books<\/code> list. Then, we check whether the index is in a valid range and specify the object via the index of the book<\/code> object in the Books<\/code> list and change its boolean field IsCheckedOut<\/code> to true<\/code>.<\/p>\nIndexOf()<\/code> method so that we get the right book back. Internally, the IndexOf()<\/code> method calls the equality comparator Equals() to compare the books.<\/strong> By default, Equals()<\/code> checks reference equality for reference types such as classes, i.e. it checks whether two object references point to the same instance in memory, not whether their content is the same.<\/p>\nBook<\/code> objects are not considered the same if they are the same object in memory, but if their Title<\/code>, Author<\/code> and ISBN<\/code> properties are the same (essentially two Book<\/code> objects representing the same actual book).<\/p>\npublic class Book(string title, string author, string isbn, bool isCheckedOut)\r\n{\r\n public string Title { get; set; } = title;\r\n\r\n public string Author { get; set; } = author;\r\n\r\n public string ISBN { get; set; } = isbn;\r\n\r\n public bool IsCheckedOut { get; set; } = isCheckedOut;\r\n\r\n public override bool Equals(object? obj)\r\n {\r\n if (obj is Book b)\r\n {\r\n return this.Title == b.Title && this.Author == b.Author && this.ISBN == b.ISBN;\r\n }\r\n else\r\n {\r\n return false;\r\n }\r\n }\r\n}<\/pre>\nEquals()<\/code> method to change its behavior so that it compares objects based on their properties (title, author, and ISBN) rather than their reference.<\/strong> This way, when IndexOf()<\/code> calls Equals()<\/code> internally, it behaves as we intend and considers two Book<\/code> objects with identical Title<\/code>, Author<\/code> and ISBN<\/code> to be the same, even if they are different instances.<\/p>\nUse the Find() Method to Find And Update a List Item<\/h3>\n
Find()<\/code> method is more flexible. It takes a predicate (a function that returns true or false) and returns the first element that fulfills the condition<\/strong>. This is useful when we need to find an element based on a complex condition.<\/p>\nFind()<\/code> method:<\/p>\npublic void CheckoutBookUsingFind(string isbn)\r\n{\r\n var bookToCheckout = Books.Find(b => b.ISBN == isbn);\r\n if (bookToCheckout is not null)\r\n {\r\n bookToCheckout.IsCheckedOut = true;\r\n }\r\n}<\/pre>\nCheckoutBookUsingFind()<\/code> method we call the Find()<\/code> method on our Books<\/code> list. As a parameter, the Find()<\/code> method accepts a lambda expression which returns us a book b<\/code> and we check whether the ISBN of b<\/code> is equal to isbn<\/code>.\u00a0 If not, the return value is null<\/code>. We store the return value in a new Book<\/code> object bookToCheckout<\/code> and check if bookToCheckout<\/code> is null. If the Find()<\/code> method returns an object, we then change the IsCheckedOut<\/code> property of it to true<\/code>.<\/p>\nList Item Update Using FindIndex() Method<\/h3>\n
FindIndex()<\/code> returns the index of the first element that fulfills a specific predicate<\/strong>. This is useful when we need the position of an element in the list, not just the element itself.<\/p>\nFindIndex()<\/code> method:<\/p>\npublic void CheckoutBookUsingFindIndex(string isbn)\r\n{\r\n var index = Books.FindIndex(b => b.ISBN == isbn);\r\n if (index != -1)\r\n {\r\n Books[index].IsCheckedOut = true;\r\n }\r\n}<\/pre>\nCheckoutBookUsingFindIndex()<\/code> method, we call the FindIndex()<\/code> method on the Books<\/code> list. We use the same condition as we used in our previously created CheckoutBookUsingFind()<\/code> method. Instead of returning the matching object for the condition, the FindIndex()<\/code> method returns the index of the matching object in our Books<\/code> list. We then check the return value. If it is not negative, we check out the book using the index of it on our Books<\/code> list.<\/p>\nUse LINQ to Find and Update <\/span><\/span>a List Item<\/span><\/span><\/h2>\n
Use LINQ FirstOrDefault() Method<\/h3>\n