:: Scope Resolution Operator
Runs a parent class method from within a subclass method.
cClassName::cMethod
Remarks
The :: operator is used to execute a parent class method from within a subclass method. When you create a subclass, the subclass methods are automatically inherited from the parent class. The :: operator makes it possible for you to execute the parent class method in the subclass method and then perform additional processing for the subclass method. The subclass definitions in the example demonstrate how the :: operator is used to execute the parent class method within a subclass method.
For additional information about the :: scope resolution operator, see Object-Oriented Programming.
Example
The following example creates a form and adds two command buttons to the form. By clicking either button, you can exit the form – the second button, cmdAnotherButton
, calls the Click procedure from cmdQuit
. This action is possible because of subclassing. The scope resolution operator calls the parent class code for the subclassed object.
frmMyForm = CREATEOBJECT("Form")
frmMyForm.Width = 450
frmMyForm.Height = 100
frmMyForm.Caption = "Scope Resolution Example"
frmMyForm.AutoCenter =.T.
frmMyForm.AddObject("cmdQuit","cmdQuitButton")
frmMyForm.AddObject("cmdAnother","cmdAnotherButton")
frmMyForm.SHOW && Display the form
READ EVENTS && Start event processing
The following example defines two command buttons. The first button will be used to subclass the second button. The subclassing can be seen by the FontBold and ForeColor properties which are defined for cmdQuit
, but never explicitly set for the cmdAnotherButton
. We are defining cmdAnotherButton
to be a subclass of the cmdQuitButton
. As a result, this button will pick up all the attributes defined above for cmdQuitButton
.
DEFINE CLASS cmdQuitButton AS CommandButton
Caption = "\<Quit" && Caption on command button
Left = 175 && Left edge of button
Top = 60 && Position for top of button
Height = 25 && Button height
Visible = .T. && Show button on form
FontItalic = .T. && Turn on italic text
ForeColor = RGB(0,0,255) && Change button text color
PROCEDURE Click
WAIT WINDOW "Executing the CLICK procedure for cmdQuit." TIMEOUT 1
CLEAR EVENTS && Stop event processing
ENDDEFINE
DEFINE CLASS cmdAnotherButton AS cmdQuitButton
Caption = "Click to quit"
Left = 175
Top = 30
Height = 25
PROCEDURE Click
WAIT WINDOW "Click event for button: cmdAnotherButton" TIMEOUT 1
cmdQuitButton::Click
ENDDEFINE
See Also
Reference
ADD CLASS Command
CREATE CLASS Command
CREATE CLASSLIB Command
CREATEOBJECT( ) Function
DEFINE CLASS Command
DODEFAULT( ) Function
GETOBJECT( ) Function
MODIFY CLASS Command
RELEASE CLASSLIB Command
SET CLASSLIB Command
WITH ... ENDWITH Command
Operators (Visual FoxPro)