Shared Members

Shared members are fields and properties that are shared by all instances of a class. Some programming languages refer to such items as static members .

Shared fields and properties are useful when you have information that is part of a class, but is not specific to any one instance of a class. Normal fields and properties exist independently for each instance of a class. Changing the value of a field or property associated with any one instance does not affect the value of fields or properties of other instances of the class. On the other hand, when you change the value of a shared field and property associated with an instance of a class, you change the value associated with all instances of the class. In this way, shared fields and properties behave like global variables that can be accessed only from instances of a class. Without static fields and properties, you would need to use module-level variables to achieve the same effect. However, module-level variables can make your classes difficult to understand and maintain. Furthermore, using module-level variables in this way violates the concept of encapsulation that classes represent.

Shared procedures are not implicitly passed instances of the class. For this reason, no unqualified references to non-shared data members are allowed in shared methods.

Shared Members Example

The following example creates a shared field (Barney) in another class (PublicFields), and demonstrates how shared members operate in code:

BegClass Form1 Extends(System.Windows.Forms.Form) Access(*Public)
    DclFld button2 Type(System.Windows.Forms.Button) Access(*Private) WithEvents(*Yes)
    DclFld button1 Type(System.Windows.Forms.Button) Access(*Private) WithEvents(*Yes)        

    BegSr button1_Click Access(*Private) Event(*this.button1.Click)
        DclSrParm sender Type(*Object)
        DclSrParm e Type(System.EventArgs)

      //Don't need to Instance the Class if the Field is Shared (*Yes)         
      MsgBox PublicFields.Barney
    EndSr
        
    BegSr button2_Click Access(*Private) Event(*this.button2.Click)
        DclSrParm sender Type(*Object)
        DclSrParm e Type(System.EventArgs)
      MsgBox PublicFields.Barney
      PublicFields.Barney = "Pence"
    EndSr
EndClass

/* _________________________________________ */
/* Contents of the Class called PublicFields */

BegClass PublicFields Access(*Public) 
    DclFld Fred Type( *String ) Access( *Public ) Inz( "Flintstone" )
    DclFld Barney Type( *String ) Access( *Public ) Inz( "Rubble" ) Shared( *Yes ) 
EndClass

Shared Members

Shared Members Example

See Also