Published fields or methods? 1

[Farahani]

Hi,

Can anybody tell me the benefits of a published field or method ?

 

[Stretchwickster]

Here is some info from Marco Cantu's Mastering Delphi 6 book:

" The published Keyword
Along with the

 public, protected

and

 private

access directives, you can use a fourth one, called

 published

. For any

 published

field, property, or method, the compiler generates extended RTTI [Run-Time Type Information] information, so that Delphi's run time environment or a program can query a class for its published interface. For example, every Delphi component has a published interface that is used by the IDE [Integrated Development Environment], in particular the Object Inspector. A regular use of

 published

fields is important when you write components. Usually, the

 published

part of a component contains no fields or methods but properties and events.

When Delphi generates a form or data module, it places the definitions of its components and methods (the event handlers) in the first portion of its definition, before the

 public

and

 private

keywords. These fields and methods of the initial portion of the class are

 published

. The default is

 published

when no special keyword is added before an element of a component class."

Hope this helps!
Clive

 

[bbegley]

A published field can let you allow access to Fields without letting the end user edit the field itself.

For example

Private
FDate : TDateTime
function GetDate:TDateTime;
function SetDate(ADate:TDateTime):boolean;
published
property Date:TDateTime read GetDate write SetDate;

This is a fake example, but you can see that it lets you edit and read a property via functions (which may include necessary validations) rather than letting the user directly edit a field value. The user has no real access to FDate, but must access it through the read write functions of the published property.

 

[TealWren]

Actually, you can have properties that are not published as well. It is properties that allow you to use get/set functions.

As Stretchwickster mentioned, being in the published gives the property RTTI info which allows it to show up in the object inspector. It also allows you to query at runtime for whether that property exists. For example using RTTI and the published property ReadOnly that exists for most components you could write a generic function like below to set the readonly property if it exists.


uses typinfo;
procedure SetReadOnly(someComponent: TComponent);
var propInfo: pPropInfo;
begin
{Get read only property if it exists}
propInfo := GetPropInfo(someComponent.ClassInfo, 'ReadOnly')
if assigned(propInfo) then
{Set read only to true}
SetEnumProp(someComponent, propInfo, 'True');
end;
TealWren

 

[Farahani]

Hi again!

Thanks for your answers, but these don't solve my problem!
I am familiar with published keyword and component writing, but I can't understand published fields & methods.

unlike published proprties & events, published field & methods don't appear in Object Inspector (? - I didn't test this) and GetPropInfo doesn't apply to them.

Bye!