ListBox.ObjectCollection Class
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ListBox.ObjectCollection Class


Represents the collection of items in a ListBox.

Namespace:   System.Windows.Forms
Assembly:  System.Windows.Forms (in System.Windows.Forms.dll)


public class ObjectCollection : IList, ICollection, IEnumerable


Initializes a new instance of ListBox.ObjectCollection.

System_CAPS_pubmethodListBox.ObjectCollection(ListBox, Object[])

Initializes a new instance of ListBox.ObjectCollection containing an array of objects.

System_CAPS_pubmethodListBox.ObjectCollection(ListBox, ListBox.ObjectCollection)

Initializes a new instance of ListBox.ObjectCollection based on another ListBox.ObjectCollection.


Gets the number of items in the collection.


Gets a value indicating whether the collection is read-only.


Gets or sets the item at the specified index within the collection.


Adds an item to the list of items for a ListBox.


Adds an array of items to the list of items for a ListBox.


Adds the items of an existing ListBox.ObjectCollection to the list of items in a ListBox.


Removes all items from the collection.


Determines whether the specified item is located within the collection.

System_CAPS_pubmethodCopyTo(Object[], Int32)

Copies the entire collection into an existing array of objects at a specified location within the array.


Determines whether the specified object is equal to the current object.(Inherited from Object.)


Allows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection.(Inherited from Object.)


Returns an enumerator to use to iterate through the item collection.


Serves as the default hash function. (Inherited from Object.)


Gets the Type of the current instance.(Inherited from Object.)


Returns the index within the collection of the specified item.

System_CAPS_pubmethodInsert(Int32, Object)

Inserts an item into the list box at the specified index.


Creates a shallow copy of the current Object.(Inherited from Object.)


Removes the specified object from the collection.


This API supports the product infrastructure and is not intended to be used directly from your code. Removes the item at the specified index within the collection.


Returns a string that represents the current object.(Inherited from Object.)

System_CAPS_pubinterfaceSystem_CAPS_privmethodICollection.CopyTo(Array, Int32)

This API supports the product infrastructure and is not intended to be used directly from your code. Copies the elements of the collection to an array, starting at a particular array index.


This API supports the product infrastructure and is not intended to be used directly from your code. Adds an object to the ListBox class.


Overloaded. Enables parallelization of a query.(Defined by ParallelEnumerable.)


Overloaded. Converts an IEnumerable to an IQueryable.(Defined by Queryable.)


Casts the elements of an IEnumerable to the specified type.(Defined by Enumerable.)


Filters the elements of an IEnumerable based on a specified type.(Defined by Enumerable.)

The ListBox.ObjectCollection class stores the items displayed in the ListBox. There are two other collections defined within the ListBox class that enable you to determine what items are selected within this collection. The ListBox.SelectedObjectCollection class provides properties and methods for determining what items are selected within the ListBox.ObjectCollection, while the ListBox.SelectedIndexCollection class enables you to determine what indexes within the ListBox.ObjectCollection are selected.

There are a number of ways to add items to the collection. The Add method provides the ability to add a single object to the collection. To add a number of objects to the collection, you create an array of items and assign it to the AddRange method. If you want to insert an object at a specific location within the collection, you can use the Insert method. To remove items, you can use either the Remove method or the RemoveAt method if you know where the item is located within the collection. The Clear method enables you to remove all items from the collection instead of using the Remove method to remove a single item at a time.

You can also manipulate the items of a ListBox by using the DataSource property. If you use the DataSource property to add items to a ListBox, you can view the items in the ListBox using the Items property but you cannot add or remove items from the list using the methods of the ListBox.ObjectCollection.

In addition to methods and properties for adding and removing items, the ListBox.ObjectCollection also provides methods to find items within the collection. The Contains method enables you to determine whether an object is a member of the collection. Once you know that the item is located within the collection, you can use the IndexOf method to determine where the item is located within the collection.

The following code example demonstrates an owner-drawn ListBox by setting the DrawMode property to the OwnerDrawVariable value and handling the DrawItem and MeasureItem events. It also demonstrates setting the BorderStyle and ScrollAlwaysVisible properties and using the AddRange method.

To run this example, paste it into an empty form that imports the System.Drawing namespace and the System.Windows.Forms namespace. Call InitializeOwnerDrawnListBox from the form's constructor or Load method.

internal System.Windows.Forms.ListBox ListBox1;

private void InitializeOwnerDrawnListBox()
	this.ListBox1 = new System.Windows.Forms.ListBox();

	// Set the location and size.
	ListBox1.Location = new Point(20, 20);
	ListBox1.Size = new Size(240, 240);

	// Populate the ListBox.ObjectCollection property 
	// with several strings, using the AddRange method.
	this.ListBox1.Items.AddRange(new object[]{"System.Windows.Forms", 
		"System.Drawing", "System.Xml", "System.Net", "System.Runtime.Remoting", 

	// Turn off the scrollbar.
	ListBox1.ScrollAlwaysVisible = false;

	// Set the border style to a single, flat border.
	ListBox1.BorderStyle = BorderStyle.FixedSingle;

	// Set the DrawMode property to the OwnerDrawVariable value. 
	// This means the MeasureItem and DrawItem events must be 
	// handled.
	ListBox1.DrawMode = DrawMode.OwnerDrawVariable;
	ListBox1.MeasureItem += 
		new MeasureItemEventHandler(ListBox1_MeasureItem);
	ListBox1.DrawItem += new DrawItemEventHandler(ListBox1_DrawItem);


// Handle the DrawItem event for an owner-drawn ListBox.
private void ListBox1_DrawItem(object sender, DrawItemEventArgs e)

	// If the item is the selected item, then draw the rectangle
	// filled in blue. The item is selected when a bitwise And  
	// of the State property and the DrawItemState.Selected 
	// property is true.
	if ((e.State & DrawItemState.Selected) == DrawItemState.Selected)
		e.Graphics.FillRectangle(Brushes.CornflowerBlue, e.Bounds);
		// Otherwise, draw the rectangle filled in beige.
		e.Graphics.FillRectangle(Brushes.Beige, e.Bounds);

	// Draw a rectangle in blue around each item.
	e.Graphics.DrawRectangle(Pens.Blue, e.Bounds);

	// Draw the text in the item.
		this.Font, Brushes.Black, e.Bounds.X, e.Bounds.Y);

	// Draw the focus rectangle around the selected item.

// Handle the MeasureItem event for an owner-drawn ListBox.
private void ListBox1_MeasureItem(object sender, 
	MeasureItemEventArgs e)

	// Cast the sender object back to ListBox type.
	ListBox theListBox = (ListBox) sender;

	// Get the string contained in each item.
	string itemString = (string) theListBox.Items[e.Index];

	// Split the string at the " . "  character.
	string[] resultStrings = itemString.Split('.');

	// If the string contains more than one period, increase the 
	// height by ten pixels; otherwise, increase the height by 
	// five pixels.
	if (resultStrings.Length>2)
		e.ItemHeight += 10;
		e.ItemHeight += 5;


.NET Framework
Available since 1.1

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

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