Overriding the OnPaint Method
The basic steps for overriding any event defined in the .NET Framework are identical and are summarized in the following list.
To override an inherited event
Override the protected OnEventName method.
Call the OnEventName method of the base class from the overridden OnEventName method, so that registered delegates receive the event.
The Paint event is discussed in detail here because every Windows Forms control must override the Paint event that it inherits from Control. The base Control class does not know how a derived control needs to be drawn and does not provide any painting logic in the OnPaint method. The OnPaint method of Control simply dispatches the Paint event to registered event receivers.
Public Class FirstControl Inherits Control Public Sub New() End Sub Protected Overrides Sub OnPaint(e As PaintEventArgs) ' Call the OnPaint method of the base class. MyBase.OnPaint(e) ' Call methods of the System.Drawing.Graphics object. e.Graphics.DrawString(Text, Font, New SolidBrush(ForeColor), RectangleF.op_Implicit(ClientRectangle)) End Sub End Class
Public Class PaintEventArgs Inherits EventArgs ... Public ReadOnly Property ClipRectangle() As System.Drawing.Rectangle ... End Property Public ReadOnly Property Graphics() As System.Drawing.Graphics ... End Property ... End Class
ClipRectangle is the rectangle to be painted, and the Graphics property refers to a Graphics object. The classes in the System.Drawing namespace are managed classes that provide access to the functionality of GDI+, the new Windows graphics library. The Graphics object has methods to draw points, strings, lines, arcs, ellipses, and many other shapes.