ListBox.OnDrawItem(DrawItemEventArgs) Method

Definition

Namespace:

System.Windows.Forms

Assembly:

System.Windows.Forms.dll

Source:

ListBox.cs

Raises the DrawItem event.

protected:
 virtual void OnDrawItem(System::Windows::Forms::DrawItemEventArgs ^ e);

protected virtual void OnDrawItem (System.Windows.Forms.DrawItemEventArgs e);

abstract member OnDrawItem : System.Windows.Forms.DrawItemEventArgs -> unit
override this.OnDrawItem : System.Windows.Forms.DrawItemEventArgs -> unit

Protected Overridable Sub OnDrawItem (e As DrawItemEventArgs)

Parameters

e

DrawItemEventArgs

A DrawItemEventArgs that contains the event data.

Examples

The following code example demonstrates how to create owner-drawn ListBox items. The code uses the DrawMode property to specify that the items drawn are fixed sized and the DrawItem event to perform the drawing of each item into the ListBox. The example code uses the properties and methods of the DrawItemEventArgs class passed as a parameter to the event handler to draw the items. This example requires that a ListBox control called listBox1 has been added to a form and that the DrawItem event is handled by the event handler defined in the example code. The example also requires that items have been added to the ListBox with the text of "Apple", "Orange", and "Plum" in that order.

private ListBox ListBox1 = new ListBox();
private void InitializeListBox()
{
    ListBox1.Items.AddRange(new Object[] 
        { "Red Item", "Orange Item", "Purple Item" });
    ListBox1.Location = new System.Drawing.Point(81, 69);
    ListBox1.Size = new System.Drawing.Size(120, 95);
    ListBox1.DrawMode = DrawMode.OwnerDrawFixed;
    ListBox1.DrawItem += new DrawItemEventHandler(ListBox1_DrawItem);
    Controls.Add(ListBox1);
}

private void ListBox1_DrawItem(object sender, 
    System.Windows.Forms.DrawItemEventArgs e)
{
    // Draw the background of the ListBox control for each item.
    e.DrawBackground();
    // Define the default color of the brush as black.
    Brush myBrush = Brushes.Black;

    // Determine the color of the brush to draw each item based 
    // on the index of the item to draw.
    switch (e.Index)
    {
        case 0:
            myBrush = Brushes.Red;
            break;
        case 1:
            myBrush = Brushes.Orange;
            break;
        case 2:
            myBrush = Brushes.Purple;
            break;
    }

    // Draw the current item text based on the current Font 
    // and the custom brush settings.
    e.Graphics.DrawString(ListBox1.Items[e.Index].ToString(), 
        e.Font, myBrush, e.Bounds, StringFormat.GenericDefault);
    // If the ListBox has focus, draw a focus rectangle around the selected item.
    e.DrawFocusRectangle();
}

Private WithEvents ListBox1 As New ListBox()

Private Sub InitializeListBox() 
    ListBox1.Items.AddRange(New Object() _
        {"Red Item", "Orange Item", "Purple Item"})
    ListBox1.Location = New System.Drawing.Point(81, 69)
    ListBox1.Size = New System.Drawing.Size(120, 95)
    ListBox1.DrawMode = DrawMode.OwnerDrawFixed
    Controls.Add(ListBox1)

End Sub

Private Sub ListBox1_DrawItem(ByVal sender As Object, _
 ByVal e As System.Windows.Forms.DrawItemEventArgs) _
 Handles ListBox1.DrawItem

    ' Draw the background of the ListBox control for each item.
    e.DrawBackground()

    ' Define the default color of the brush as black.
    Dim myBrush As Brush = Brushes.Black

    ' Determine the color of the brush to draw each item based on   
    ' the index of the item to draw.
    Select Case e.Index
        Case 0
            myBrush = Brushes.Red
        Case 1
            myBrush = Brushes.Orange
        Case 2
            myBrush = Brushes.Purple
    End Select

    ' Draw the current item text based on the current 
    ' Font and the custom brush settings.
    e.Graphics.DrawString(ListBox1.Items(e.Index).ToString(), _
        e.Font, myBrush, e.Bounds, StringFormat.GenericDefault)

    ' If the ListBox has focus, draw a focus rectangle around  _ 
    ' the selected item.
    e.DrawFocusRectangle()
End Sub

Remarks

Raising an event invokes the event handler through a delegate. For more information, see Handling and Raising Events.

The OnDrawItem method also enables derived classes to handle the event without attaching a delegate. This is the preferred technique for handling the event in a derived class.

Notes to Inheritors

When overriding OnDrawItem(DrawItemEventArgs) in a derived class, be sure to call the base class's OnDrawItem(DrawItemEventArgs) method so that registered delegates receive the event.

See also

• DrawItem