Checking if Component has a Caption Property

I have a program that accesses varying components via the
TWinControl base class.  TWinControl does not have a caption
property.  I'd like to be able to set the caption property
if one exists for the component.

1) How do I check if a caption property exists for any control
   that can be selected?

2) What base class can I use that will cover all visible
   components, yet have a caption property?

3) If I have to use a try..except block...what exception will
   I have to trap?
LVL 3
mheacockAsked:
Who is Participating?
I wear a lot of hats...

"The solutions and answers provided on Experts Exchange have been extremely helpful to me over the last few years. I wear a lot of hats - Developer, Database Administrator, Help Desk, etc., so I know a lot of things but not a lot about one thing. Experts Exchange gives me answers from people who do know a lot about one thing, in a easy to use platform." -Todd S.

sperlingCommented:
Two ways of doing this.

1. As TControl has a protected Caption property, you can derive a class from TControl which simply makes Caption public, and then cast any TControl to this new type and set the Caption.

2. Use the Delphi RTTI (Run-Time Type Information) functions to check whether any object has a Caption property, and if so set it.

uses
  TypInfo;

type
  TControlFix=class(TControl)
  public
    property Caption;
  end;

procedure SetControlCaption1(Ctrl : TControl; value : STRING);
begin
  TControlFix(Ctrl).Caption := value;
end;

procedure SetControlCaption2(Ctrl : TControl; value : STRING);
var
  PropInfo  : PPropInfo;
begin
  PropInfo := GetPropInfo(Ctrl.ClassInfo, 'Caption');
  if PropInfo<>nil then begin
    SetStrProp(Ctrl, PropInfo, value);
  end;
end;


Note that the first function will set the Caption of any TControl descendant, regardless of whether the Caption is protected in the actual class. It will however not modify "new" Caption properties, only the original TControl.Caption. Also, this function will set the Text property of a TEdit, as this actually is the caption of an edit.

The second function will set the Caption if the Caption is published only. It'll not affect TEdit.

Regards,

Erik.
0

Experts Exchange Solution brought to you by

Your issues matter to us.

Facing a tech roadblock? Get the help and guidance you need from experienced professionals who care. Ask your question anytime, anywhere, with no hassle.

Start your 7-day free trial
mheacockAuthor Commented:
The number 2 of your question was exactly what I was looking for.
I didn't really want to derive any classes...I received various
comments to do this...seemed kind of a hack to me...the RTTI
stuff seems the better route.
0
It's more than this solution.Get answers and train to solve all your tech problems - anytime, anywhere.Try it for free Edge Out The Competitionfor your dream job with proven skills and certifications.Get started today Stand Outas the employee with proven skills.Start learning today for free Move Your Career Forwardwith certification training in the latest technologies.Start your trial today
Delphi

From novice to tech pro — start learning today.