PRB: Protected Property Cannot be Changed by Objects in a Class

MORE INFORMATION

Protected properties added to a container class in Visual FoxPro become part of your container class. However, objects that are added to the container in the Class Designer are not considered to be part of the container class but rather external objects sitting in the container. Because of this, protected properties are encapsulated in the container class and can not be seen by objects sitting in the container. This behavior can be confusing because the class designer gives the appearance that the container and all the objects in it are part of the container class.

Steps to Reproduce Behavior

1. Create the following program:

      ***** Start Program Code *****
      PUBLIC oForm1
      oForm1 = CREATEOBJECT("myform")
      oForm1.Show
   
      DEFINE CLASS myform AS form
        Name = "myform"
        PROTECTED cString
   
        ADD OBJECT command1 AS commandbutton WITH ;
          Top = 20, ;
          Left = 20, ;
          Height = 30, ;
          Width = 100, ;
          Caption  = "Change Property"
   
        ADD OBJECT command2 AS commandbutton WITH ;
          Top = 100, ;
          Left = 20, ;
          Height = 30, ;
          Width = 100, ;
          Caption  = "Call Method"
   
        PROCEDURE command1.Click
          * This fails because the Command button
          * Cannot change a protected property of the class
          This.Parent.cString = "Change Me"
        ENDPROC
   
        PROCEDURE command2.Click
          * calling a method to change a protected property will work
          This.Parent.ChangeString()
   
        ENDPROC
   
        PROCEDURE ChangeString
          * because the method is part of the class, it
          * can change the cString property
          This.cString = "Change Me"
          WAIT WINDOW "The Property cString now equals "+This.cString
        ENDPROC
   
      ENDDEFINE
   
      ***** End Code *****
   						

2. Run the program and click the Call Method Command button. Note that the property changes. Pressing the other button causes the error to appear.