C# ListBox Class

In Windows Forms, the ListBox control is used to show multiple elements in a list, from which a user can select one or more elements, and the elements are generally displayed in multiple columns. The ListBox class in C# is used to represent the Windows list box and also provides different types of properties, methods, and events. It is defined under System.Windows.Forms namespace.

Collections in ListBox

The ListBox class contains three different types of collection classes, which are listed below:

• ListBox.ObjectCollection: This class holds all the elements contained in the ListBox control.
• ListBox.SelectedObjectCollection: This class holds a collection of the selected items, which is a subset of the items contained in the ListBox control.
• ListBox.SelectedIndexCollection: This class holds a collection of the selected indexes, which is a subset of the indexes of the ListBox.ObjectCollection and these indexes specify elements that are selected.

Ways to Create a ListBox In Windows Forms

There are two ways to create a ListBox in Windows forms which are mentioned below.

• Drag and drop (Design-Time)
• Custom ListBox (Run-Time)

1. Drag and drop (Design-Time)

This is the easiest way to create a ListBox in Windows Forms using Visual Studio we just have to open the toolbox and drag and drop the ListBox on the form in the designer and further we can change the appearance of the ListBox using the properties. Follow these steps to create a ListBox.

Step 1: Now locate the project with the name here we are using the default name which is Form1 and it will open a form in the editor that we can further modify.

In the image, we have two files that are open one Design and there is Form1.cs these two play a major role. We use the Form 1.cs file for the custom logic.

Step 2: Now open a Toolbox go to the view > Toolbox or ctrl + alt + x.

Step 3. Now open the common controls and drag and drop the ListBox on the form where we want it to be placed.

Step 4. Now open the properties of the button right-click on the ListBox and it will open the properties solution explorer now we can change the appearance and the behaviour of the button.

Step 5: In the properties, we can make different types of changes we can add the items in the list which is available at the left-most bottom or we can click on Collection(Item) in the properties as shown in the image.

It will open the new box (String Collection Editor) here we can add different list items and each line is a separate list as shown in the image after adding the list click on the OK button.

Output:

2. Custom ListBox (Run Time)

In this method, we are going to modify the Form1.cs file and add custom code modification in C# with the help of the ListBox class. The following steps show how to create a ListBox dynamically:

Step 1: Create a ListBox control using the ListBox() constructor is provided by the ListBox class.

// Creating a ListBox control

ListBox mylist = new ListBox();

Step 2: After creating the ListBox control, set the property of the ListBox control provided by the ListBox class.

ListBox mylist = new ListBox();

mylist.Location = new Point(287, 109);

mylist.Size = new Size(120, 95);

mylist.ForeColor = Color.Purple;

mylist.Items.Add(123);

mylist.Items.Add(456);

mylist.Items.Add(789);

Step 3: And lastly add this ListBox control to the form using the following statement:

// Adding ListBox control

// to the form

this.Controls.Add(mylist);

Step 4: Double-click on the form in Design view. It will open the Form1.cs file where code is written in C#. Here. the program file is Form 1.cs Now write this code in Form1.cs file

Form1.cs file:

namespace WinFormsApp1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            // Creating and setting the 
            // properties of ListBox 
            ListBox mylist = new ListBox();
            mylist.Location = new Point(287, 109);
            mylist.Size = new Size(120, 95);
            mylist.ForeColor = Color.Purple;
            mylist.Items.Add("C#");
            mylist.Items.Add("Java");
            mylist.Items.Add("C");
            mylist.Items.Add("C++");

            // Adding ListBox control 
            // to the form 
            this.Controls.Add(mylist);
        }

    }
}

Output:

Enabling Multi-Selection in ListBox

By default, the ListBox allows selecting only one item at a time. If we allow users to select multiple items then we need to set the SelectionMode property.

SelectionMode options:

The SelectionMode options are listed below:

• SelectionMode.One: It is a default one, in this only one item can be selected.
• SelectionMode.MultiSimple: In this multiple items can be selected by clicking them.
• SelectionMode.MultiExtended: In this multiple items can be selected with Shift or Ctrl keys.

Example:

private void Form1_Load(object sender, EventArgs e)
{
    ListBox myList = new ListBox
    {
        Location = new Point(287, 109),
        Size = new Size(120, 95),
        ForeColor = Color.DarkBlue,
        // Enable multi-selection
        SelectionMode = SelectionMode.MultiExtended 
    };

    myList.Items.Add("Python");
    myList.Items.Add("JavaScript");
    myList.Items.Add("Go");
    myList.Items.Add("Ruby");

    // Handle selected index changed event
    myList.SelectedIndexChanged += (s, ev) =>
    {
        var selectedItems = ((ListBox)s).SelectedItems;
        string message = "Selected items:\n";
        foreach (var item in selectedItems)
        {
            message += item + "\n";
        }
        MessageBox.Show(message, "Selection");
    };

    this.Controls.Add(myList);
}

Explanation: Here, we are creating a ListBox where users can select multiple items and shows a message box listing their selections whenever the selection changes.

Event Handling in ListBox

The ListBox can do anything whenever the user interacts with it.

• SelectedIndexChanged: This happens when the user picks a different item in the list.
• MouseDoubleClick: This happens when the user double-clicks on the list.
• KeyDown and KeyUp: These happen when the user presses or releases a key while the list is active.

Note: These events help the program to respond what the user does with the ListBox.

// Handling selection change to update 
// other UI elements or perform actions.

myList.SelectedIndexChanged += (sender, e) =>
{
    ListBox list = (ListBox)sender;
    if (list.SelectedItem != null)
    {
        MessageBox.Show("You selected: " + list.SelectedItem.ToString());
    }
};

Constructor

ListBox(): This constructor is used to initialize a new instance of the ListBox class.

Properties

The properties of the list box class is listed below:

This property is not commonly used in ListBox as it is primarily item-based.