Assembly: System.Windows.Forms (in System.Windows.Forms.dll)
Raising an event invokes the event handler through a delegate. For more information, see Handling and Raising Events.
The 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 in a derived class, be sure to call the base class's method so that registered delegates receive the event.
The following code example is an event-raising method that is executed when the Text property value changes. The Control class has several methods with the name pattern On PropertyName Changed that raise the corresponding PropertyName Changed event when the PropertyName value changes (PropertyName represents the name of the corresponding property).
The following code example changes the ForeColor of a TextBox derived class displaying currency data. The example converts the text to a decimal number and changes the ForeColor to Color.Red if the number is negative and to Color.Black if the number is positive. This example requires that you have a class that derives from the TextBox class.
Protected Overrides Sub OnTextChanged(e As System.EventArgs) Try ' Convert the text to a Double and determine ' if it is a negative number. If Double.Parse(Me.Text) < 0 Then ' If the number is negative, display it in Red. Me.ForeColor = Color.Red Else ' If the number is not negative, display it in Black. Me.ForeColor = Color.Black End If Catch ' If there is an error, display the ' text using the system colors. Me.ForeColor = SystemColors.ControlText End Try MyBase.OnTextChanged(e) End Sub