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C# iList (How It Works For Developers)

Chipego
ByChipego Kalinda
June 6, 2024
Updated  June 22, 2025

Introduction to the IList

IList is a part of the .NET Framework's Collections namespace. It is a non-generic collection interface that provides the blueprint for a collection of objects that can be individually accessed by their index. Unlike arrays, IList allows for a dynamic number of object value elements, meaning you can add or remove elements from the collection as needed. It serves as the base interface for all non-generic lists in the .NET Framework, offering a way to manage a collection of objects in a more flexible manner than arrays. We'll learn about the IList interface and the IronPDF C# PDF Library in this tutorial.

Understanding the IList Interface

The public interface IList declaration is a fundamental part of creating custom collections in C# that adhere to the IList contract specified by the .NET Framework's Collections namespace. IList includes properties and methods that enable accessing elements in the collection, counting them, and modifying the collection by adding, inserting, or removing elements. Here are some of the key properties and methods defined in the IList interface:

  • Properties like IsFixedSize and IsReadOnly inform whether the collection is of fixed size or read-only, respectively.
  • Methods such as Add, Insert, Remove, and RemoveAt are used for modifying elements within the collection. You can add, insert, and remove elements.
  • The IndexOf method is for locating elements, and the Item property (or indexer in C#) allows for the getting and setting of elements based on their index.

Practical Usage of the IList Interface

To showcase how IList works, let's create a simple example. This example will demonstrate how to declare an IList, add items to it, and iterate over its contents.

Creating and Modifying an IList

First, let's see how to declare an IList and add items to it:

using System;
using System.Collections;

class Program
{
    static void Main(string[] args)
    {
        // Creating an IList instance
        IList myIList = new ArrayList();

        // Adding elements to the IList
        myIList.Add("Hello");
        myIList.Add(10);
        myIList.Add(new object());

        // Displaying the number of values in the IList using the Count property
        Console.WriteLine($"Number of elements: {myIList.Count}");

        // Accessing elements using a loop
        foreach (var element in myIList)
        {
            Console.WriteLine(element);
        }
    }
}
using System;
using System.Collections;

class Program
{
    static void Main(string[] args)
    {
        // Creating an IList instance
        IList myIList = new ArrayList();

        // Adding elements to the IList
        myIList.Add("Hello");
        myIList.Add(10);
        myIList.Add(new object());

        // Displaying the number of values in the IList using the Count property
        Console.WriteLine($"Number of elements: {myIList.Count}");

        // Accessing elements using a loop
        foreach (var element in myIList)
        {
            Console.WriteLine(element);
        }
    }
}
Imports System
Imports System.Collections

Friend Class Program
	Shared Sub Main(ByVal args() As String)
		' Creating an IList instance
		Dim myIList As IList = New ArrayList()

		' Adding elements to the IList
		myIList.Add("Hello")
		myIList.Add(10)
		myIList.Add(New Object())

		' Displaying the number of values in the IList using the Count property
		Console.WriteLine($"Number of elements: {myIList.Count}")

		' Accessing elements using a loop
		For Each element In myIList
			Console.WriteLine(element)
		Next element
	End Sub
End Class
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In the above example, we've created an IList instance using ArrayList, a class that implements IList. We've added a mix of different types of objects to demonstrate that an IList can hold any object. Finally, we've iterated over the collection, printing out each element.

Index-Based Access and Modification

Accessing and modifying elements by their index is a key feature of IList. The following example shows how you can do it:

using System;
using System.Collections;

class Program
{
    static void Main(string[] args)
    {
        IList myIList = new ArrayList { "Hello", 10, new object() };

        // Accessing an element by index
        object value = myIList[1];
        Console.WriteLine($"Element at index 1: {value}");

        // Modifying an element by index
        myIList[1] = 20;
        Console.WriteLine($"Modified element at index 1: {myIList[1]}");
    }
}
using System;
using System.Collections;

class Program
{
    static void Main(string[] args)
    {
        IList myIList = new ArrayList { "Hello", 10, new object() };

        // Accessing an element by index
        object value = myIList[1];
        Console.WriteLine($"Element at index 1: {value}");

        // Modifying an element by index
        myIList[1] = 20;
        Console.WriteLine($"Modified element at index 1: {myIList[1]}");
    }
}
Imports System
Imports System.Collections

Friend Class Program
	Shared Sub Main(ByVal args() As String)
		Dim myIList As IList = New ArrayList From { "Hello", 10, New Object() }

		' Accessing an element by index
		Dim value As Object = myIList(1)
		Console.WriteLine($"Element at index 1: {value}")

		' Modifying an element by index
		myIList(1) = 20
		Console.WriteLine($"Modified element at index 1: {myIList(1)}")
	End Sub
End Class
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Implementing a Custom IList

Sometimes, you might need a tailored collection that inherits IList. This allows for more control over how elements are stored, accessed, and modified. Below is an example of a simple custom collection implementing IList:

using System;
using System.Collections;

public class CustomCollection : IList
{
    private ArrayList _innerList = new ArrayList();

    public object this[int index]
    {
        get => _innerList[index];
        set => _innerList[index] = value;
    }

    public bool IsFixedSize => _innerList.IsFixedSize;
    public bool IsReadOnly => _innerList.IsReadOnly;
    public int Count => _innerList.Count;
    public bool IsSynchronized => _innerList.IsSynchronized;
    public object SyncRoot => _innerList.SyncRoot;

    public int Add(object value)
    {
        return _innerList.Add(value);
    }

    public void Clear()
    {
        _innerList.Clear();
    }

    public bool Contains(object value)
    {
        return _innerList.Contains(value);
    }

    public int IndexOf(object value)
    {
        return _innerList.IndexOf(value);
    }

    public void Insert(int index, object value)
    {
        _innerList.Insert(index, value);
    }

    public void Remove(object value)
    {
        _innerList.Remove(value);
    }

    public void RemoveAt(int index)
    {
        _innerList.RemoveAt(index);
    }

    public void CopyTo(Array array, int index)
    {
        _innerList.CopyTo(array, index);
    }

    public IEnumerator GetEnumerator()
    {
        return _innerList.GetEnumerator();
    }
}
using System;
using System.Collections;

public class CustomCollection : IList
{
    private ArrayList _innerList = new ArrayList();

    public object this[int index]
    {
        get => _innerList[index];
        set => _innerList[index] = value;
    }

    public bool IsFixedSize => _innerList.IsFixedSize;
    public bool IsReadOnly => _innerList.IsReadOnly;
    public int Count => _innerList.Count;
    public bool IsSynchronized => _innerList.IsSynchronized;
    public object SyncRoot => _innerList.SyncRoot;

    public int Add(object value)
    {
        return _innerList.Add(value);
    }

    public void Clear()
    {
        _innerList.Clear();
    }

    public bool Contains(object value)
    {
        return _innerList.Contains(value);
    }

    public int IndexOf(object value)
    {
        return _innerList.IndexOf(value);
    }

    public void Insert(int index, object value)
    {
        _innerList.Insert(index, value);
    }

    public void Remove(object value)
    {
        _innerList.Remove(value);
    }

    public void RemoveAt(int index)
    {
        _innerList.RemoveAt(index);
    }

    public void CopyTo(Array array, int index)
    {
        _innerList.CopyTo(array, index);
    }

    public IEnumerator GetEnumerator()
    {
        return _innerList.GetEnumerator();
    }
}
Imports System
Imports System.Collections

Public Class CustomCollection
	Implements IList

	Private _innerList As New ArrayList()

	Default Public Property Item(ByVal index As Integer) As Object Implements IList.Item
		Get
			Return _innerList(index)
		End Get
		Set(ByVal value As Object)
			_innerList(index) = value
		End Set
	End Property

	Public ReadOnly Property IsFixedSize() As Boolean Implements IList.IsFixedSize
		Get
			Return _innerList.IsFixedSize
		End Get
	End Property
	Public ReadOnly Property IsReadOnly() As Boolean Implements IList.IsReadOnly
		Get
			Return _innerList.IsReadOnly
		End Get
	End Property
	Public ReadOnly Property Count() As Integer Implements System.Collections.ICollection.Count
		Get
			Return _innerList.Count
		End Get
	End Property
	Public ReadOnly Property IsSynchronized() As Boolean Implements System.Collections.ICollection.IsSynchronized
		Get
			Return _innerList.IsSynchronized
		End Get
	End Property
	Public ReadOnly Property SyncRoot() As Object Implements System.Collections.ICollection.SyncRoot
		Get
			Return _innerList.SyncRoot
		End Get
	End Property

	Public Function Add(ByVal value As Object) As Integer Implements IList.Add
		Return _innerList.Add(value)
	End Function

	Public Sub Clear() Implements IList.Clear
		_innerList.Clear()
	End Sub

	Public Function Contains(ByVal value As Object) As Boolean Implements IList.Contains
		Return _innerList.Contains(value)
	End Function

	Public Function IndexOf(ByVal value As Object) As Integer Implements IList.IndexOf
		Return _innerList.IndexOf(value)
	End Function

	Public Sub Insert(ByVal index As Integer, ByVal value As Object) Implements IList.Insert
		_innerList.Insert(index, value)
	End Sub

	Public Sub Remove(ByVal value As Object) Implements IList.Remove
		_innerList.Remove(value)
	End Sub

	Public Sub RemoveAt(ByVal index As Integer) Implements IList.RemoveAt
		_innerList.RemoveAt(index)
	End Sub

	Public Sub CopyTo(ByVal array As Array, ByVal index As Integer) Implements System.Collections.ICollection.CopyTo
		_innerList.CopyTo(array, index)
	End Sub

	Public Function GetEnumerator() As IEnumerator Implements System.Collections.IEnumerable.GetEnumerator
		Return _innerList.GetEnumerator()
	End Function
End Class
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This CustomCollection class encapsulates an ArrayList, a class that itself implements IList. Our CustomCollection forwards calls to the underlying ArrayList, allowing it to behave like any other collection that implements IList. This example demonstrates creating a collection that can be accessed by index, modified (items added, inserted, or removed), and iterated over, just like any built-in .NET collection that implements IList.

Advanced Operations with IList

Beyond basic add, remove, and access operations, IList allows for more complex manipulations and queries. For instance, checking if the collection contains a specific object or finding the index of an object within the collection are operations that can be essential for certain applications:

using System;
using System.Collections;

class Program
{
    static void Main(string[] args)
    {
        IList myIList = new ArrayList { "Hello", 10, new object() };

        // Check if the IList contains a specific object
        bool contains = myIList.Contains(10); // Assuming 10 was added previously
        Console.WriteLine($"Contains 10: {contains}");

        // Find the index of a specific object
        int index = myIList.IndexOf(10);
        Console.WriteLine($"Index of 10: {index}");
    }
}
using System;
using System.Collections;

class Program
{
    static void Main(string[] args)
    {
        IList myIList = new ArrayList { "Hello", 10, new object() };

        // Check if the IList contains a specific object
        bool contains = myIList.Contains(10); // Assuming 10 was added previously
        Console.WriteLine($"Contains 10: {contains}");

        // Find the index of a specific object
        int index = myIList.IndexOf(10);
        Console.WriteLine($"Index of 10: {index}");
    }
}
Imports System
Imports System.Collections

Friend Class Program
	Shared Sub Main(ByVal args() As String)
		Dim myIList As IList = New ArrayList From { "Hello", 10, New Object() }

		' Check if the IList contains a specific object
		Dim contains As Boolean = myIList.Contains(10) ' Assuming 10 was added previously
		Console.WriteLine($"Contains 10: {contains}")

		' Find the index of a specific object
		Dim index As Integer = myIList.IndexOf(10)
		Console.WriteLine($"Index of 10: {index}")
	End Sub
End Class
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These operations can be particularly useful when dealing with collections of objects where you need to determine the presence or position of specific items without iterating over the entire collection.

IronPDF: C# PDF Library

C# iList (How It Works For Developers): Figure 1 - IronPDF

IronPDF is a PDF library for .NET developers that allows for the creation and manipulation of PDF documents directly within .NET applications. It supports converting HTML to PDF documents, images, and web pages to PDF. Developers can easily add PDF functionalities to their applications with this library. IronPDF also includes features for editing, merging, and splitting PDF files, which provide comprehensive control over PDF manipulation.

IronPDF excels in HTML to PDF conversion, ensuring precise preservation of original layouts and styles. It's perfect for creating PDFs from web-based content such as reports, invoices, and documentation. With support for HTML files, URLs, and raw HTML strings, IronPDF easily produces high-quality PDF documents.

using IronPdf;

class Program
{
    static void Main(string[] args)
    {
        var renderer = new ChromePdfRenderer();

        // 1. Convert HTML String to PDF
        var htmlContent = "<h1>Hello, IronPDF!</h1><p>This is a PDF from an HTML string.</p>";
        var pdfFromHtmlString = renderer.RenderHtmlAsPdf(htmlContent);
        pdfFromHtmlString.SaveAs("HTMLStringToPDF.pdf");

        // 2. Convert HTML File to PDF
        var htmlFilePath = "path_to_your_html_file.html"; // Specify the path to your HTML file
        var pdfFromHtmlFile = renderer.RenderHtmlFileAsPdf(htmlFilePath);
        pdfFromHtmlFile.SaveAs("HTMLFileToPDF.pdf");

        // 3. Convert URL to PDF
        var url = "http://ironpdf.com"; // Specify the URL
        var pdfFromUrl = renderer.RenderUrlAsPdf(url);
        pdfFromUrl.SaveAs("URLToPDF.pdf");
    }
}
using IronPdf;

class Program
{
    static void Main(string[] args)
    {
        var renderer = new ChromePdfRenderer();

        // 1. Convert HTML String to PDF
        var htmlContent = "<h1>Hello, IronPDF!</h1><p>This is a PDF from an HTML string.</p>";
        var pdfFromHtmlString = renderer.RenderHtmlAsPdf(htmlContent);
        pdfFromHtmlString.SaveAs("HTMLStringToPDF.pdf");

        // 2. Convert HTML File to PDF
        var htmlFilePath = "path_to_your_html_file.html"; // Specify the path to your HTML file
        var pdfFromHtmlFile = renderer.RenderHtmlFileAsPdf(htmlFilePath);
        pdfFromHtmlFile.SaveAs("HTMLFileToPDF.pdf");

        // 3. Convert URL to PDF
        var url = "http://ironpdf.com"; // Specify the URL
        var pdfFromUrl = renderer.RenderUrlAsPdf(url);
        pdfFromUrl.SaveAs("URLToPDF.pdf");
    }
}
Imports IronPdf

Friend Class Program
	Shared Sub Main(ByVal args() As String)
		Dim renderer = New ChromePdfRenderer()

		' 1. Convert HTML String to PDF
		Dim htmlContent = "<h1>Hello, IronPDF!</h1><p>This is a PDF from an HTML string.</p>"
		Dim pdfFromHtmlString = renderer.RenderHtmlAsPdf(htmlContent)
		pdfFromHtmlString.SaveAs("HTMLStringToPDF.pdf")

		' 2. Convert HTML File to PDF
		Dim htmlFilePath = "path_to_your_html_file.html" ' Specify the path to your HTML file
		Dim pdfFromHtmlFile = renderer.RenderHtmlFileAsPdf(htmlFilePath)
		pdfFromHtmlFile.SaveAs("HTMLFileToPDF.pdf")

		' 3. Convert URL to PDF
		Dim url = "http://ironpdf.com" ' Specify the URL
		Dim pdfFromUrl = renderer.RenderUrlAsPdf(url)
		pdfFromUrl.SaveAs("URLToPDF.pdf")
	End Sub
End Class
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Code Example

Here is a straightforward example that demonstrates generating a simple PDF document from a list of strings using IronPDF and the IList interface:

using IronPdf;
using System.Collections.Generic;

public class PDFGenerator
{
    public static void GeneratePDFFromList(IList<string> dataList)
    {
        // Initialize the HtmlToPdf renderer
        var renderer = new ChromePdfRenderer();

        // Start building HTML content from the dataList
        var htmlContent = "<h1>My Data List</h1><ul>";
        foreach (var item in dataList)
        {
            htmlContent += $"<li>{item}</li>";
        }
        htmlContent += "</ul>";

        // Convert HTML string to PDF
        var pdfDocument = renderer.RenderHtmlAsPdf(htmlContent);

        // Save the PDF to a file
        pdfDocument.SaveAs("DataList.pdf");
    }
}

// Example usage
class Program
{
    static void Main(string[] args)
    {
        License.LicenseKey = "License-Key";
        IList<string> myDataList = new List<string> { "Apple", "Banana", "Cherry" };
        PDFGenerator.GeneratePDFFromList(myDataList);
    }
}
using IronPdf;
using System.Collections.Generic;

public class PDFGenerator
{
    public static void GeneratePDFFromList(IList<string> dataList)
    {
        // Initialize the HtmlToPdf renderer
        var renderer = new ChromePdfRenderer();

        // Start building HTML content from the dataList
        var htmlContent = "<h1>My Data List</h1><ul>";
        foreach (var item in dataList)
        {
            htmlContent += $"<li>{item}</li>";
        }
        htmlContent += "</ul>";

        // Convert HTML string to PDF
        var pdfDocument = renderer.RenderHtmlAsPdf(htmlContent);

        // Save the PDF to a file
        pdfDocument.SaveAs("DataList.pdf");
    }
}

// Example usage
class Program
{
    static void Main(string[] args)
    {
        License.LicenseKey = "License-Key";
        IList<string> myDataList = new List<string> { "Apple", "Banana", "Cherry" };
        PDFGenerator.GeneratePDFFromList(myDataList);
    }
}
Imports IronPdf
Imports System.Collections.Generic

Public Class PDFGenerator
	Public Shared Sub GeneratePDFFromList(ByVal dataList As IList(Of String))
		' Initialize the HtmlToPdf renderer
		Dim renderer = New ChromePdfRenderer()

		' Start building HTML content from the dataList
		Dim htmlContent = "<h1>My Data List</h1><ul>"
		For Each item In dataList
			htmlContent &= $"<li>{item}</li>"
		Next item
		htmlContent &= "</ul>"

		' Convert HTML string to PDF
		Dim pdfDocument = renderer.RenderHtmlAsPdf(htmlContent)

		' Save the PDF to a file
		pdfDocument.SaveAs("DataList.pdf")
	End Sub
End Class

' Example usage
Friend Class Program
	Shared Sub Main(ByVal args() As String)
		License.LicenseKey = "License-Key"
		Dim myDataList As IList(Of String) = New List(Of String) From {"Apple", "Banana", "Cherry"}
		PDFGenerator.GeneratePDFFromList(myDataList)
	End Sub
End Class
$vbLabelText   $csharpLabel

In this example, an IList<string> is used to store a collection of fruit names. The GeneratePDFFromList method then iterates over this list, building an HTML string that includes each item in an unordered list. IronPDF's ChromePdfRenderer converts this HTML content into a PDF document, which is subsequently saved to a file.

C# iList (How It Works For Developers): Figure 2 - PDF Output

Conclusion

C# iList (How It Works For Developers): Figure 3 - Licensing

This beginner-friendly guide aimed to cover the basics and practical uses of IList in C#. With examples ranging from simple usage to custom implementation, it's clear that IList is a powerful tool in the C# developer's toolkit. Whether you're manipulating collections of data or building your collection types, IList offers the functionality and flexibility needed for effective software development. IronPDF offers a free trial of its PDF library for interested users, with licenses available starting from $749.

Frequently Asked Questions

What is the IList interface in C#?

IList is a non-generic collection interface in the .NET Framework's Collections namespace that provides a blueprint for collections of objects that can be accessed by index. It allows for a dynamic number of elements and supports operations like adding, inserting, and removing elements.

How does IList differ from arrays in C#?

Unlike arrays, IList allows for a dynamic number of elements, meaning you can add or remove elements as needed. Arrays have a fixed size once initialized, while IList collections can grow or shrink.

What are some key properties and methods of the IList interface?

Key properties of IList include IsFixedSize and IsReadOnly, which indicate if the collection has a fixed size or is read-only. Methods include Add, Insert, Remove, RemoveAt, and IndexOf, which manage and access elements in the collection.

Can you give an example of creating and modifying an IList?

You can create an IList using the ArrayList class, which implements IList. For example, you can add elements using the Add method and access elements using a loop or by index. Modifications can be done using methods like Insert and RemoveAt.

How can you implement a custom IList in C#?

To implement a custom IList, create a class that encapsulates an ArrayList or another IList implementation. Override the necessary methods and properties such as Add, Remove, IndexOf, and others to tailor the collection's behavior.

How can you generate a PDF from a collection of data?

You can use IronPDF, a PDF library for .NET developers, to generate PDF documents from collections of data. It allows converting HTML strings, files, or URLs into PDFs, which can be particularly useful when working with IList.

How does the library convert HTML to PDF?

IronPDF uses the ChromePdfRenderer class to convert HTML content into PDF documents. It supports converting HTML strings, files, and URLs, making it versatile for creating PDFs from various web-based content.

What are the advanced operations available with the IList interface?

Advanced operations with IList include checking if the collection contains a specific object using Contains and finding the index of an object using IndexOf. These operations are useful for managing collections without iterating through all elements.

How can you generate a PDF from an IList using a library?

You can generate a PDF from an IList by iterating over the list to build an HTML string and then using IronPDF's ChromePdfRenderer to convert this HTML content into a PDF document. The PDF can be saved to a file using the SaveAs method.

Where can I find a free trial of the PDF library?

IronPDF offers a free trial of its PDF library, which can be accessed through their website. Licenses for the library start from the liteLicense package.

Chipego
Chipego Kalinda
  Chat with engineering team now
Software Engineer
Chipego has a natural skill for listening that helps him to comprehend customer issues, and offer intelligent solutions. He joined the Iron Software team in 2023, after studying a Bachelor of Science in Information Technology. IronPDF and IronOCR are the two products Chipego has been focusing on, but his knowledge of all products is growing daily, as he finds new ways to support customers. He enjoys how collaborative life is at Iron Software, with team members from across the company bringing their varied experience to contribute to effective, innovative solutions. When Chipego is away from his desk, he can often be found enjoying a good book or playing football.

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