Adding Fields and Properties to a Class

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You can use both fields and properties to store information in an object. Although fields and properties are almost indistinguishable from a client-application perspective, they are declared differently within a class. Whereas fields are simply public variables that a class exposes, properties use Property procedures to control how values are set or returned.

To add a field to a class

Declare a public variable in the class definition, as in the following code:

BegClass Form1 Extends(System.Windows.Forms.Form) Access(*Pub)
  DclFld button2 Type(System.Windows.Forms.Button) Access(*Private)
EndClass

To add a property to a class

Declare a local variable within the class to store the property value. This step is necessary because properties do not allocate any storage on their own. To protect their values from direct modification, variables used to store property values should be declared as *Private.
Preface property declarations with modifiers, such as *Public and *Shared, as appropriate.
Use BEGGET and BEGSET commands within the property definition BEGPROP. Get property procedures are used to return the value of a property and are roughly equivalent to functions in syntax. They accept no arguments and can be used to return the value of private local variables declared within the class used to store the property value. Set property procedures are used to set the value of a property; they have a parameter, NewValueName , with the same data type as the property itself. Whenever the value of the property is changed, Value is passed to the Set property procedure, where it can be validated and stored in a local variable.
Terminate BEGGET and BEGSET property procedures with EndGet and EndSet commands as appropriate.
Terminate the property block with an ENDPROP command.

The following example declares a property in a class:

 BegClass ThisClass 
    BegProp Prop1 Type( *Integer ) len( 4 ) Access( *Public )<br />       BegGet<br />          LeaveSR 5<br />       EndGet<br />         BegSet newvalname( Myname )   C = A * B<br />          zero[1] = D<br />       EndSet<br />    EndProp <br /> EndClass

When you create an instance of ThisClass and set the value of the property One, the Set property procedure is called and the value is passed in the Value parameter, which is stored in a local variable named Myname. When the value of this property is retrieved, the Get property procedure is called like a function and returns the value stored in the local variable Prop1.

Adding Fields and Properties to a Class

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