asked on

Component help

You know when you drop and 2 or 3 ImageLists on a form, and they show up in the object inspector for a ListView - LargeImage List ... for an example ..

Well how do i go about doing this with a component that I am creating? How do I access all the properties, methods and event of the imagelist?

Can somebody provide me with a good example of a component that does this.

Thanks

Stuart_Johnson

Hi Romans,

Im not sure if I follow what you mean. Do you want your component to be able to access the properties of a listview on a form, or do you want to create a listview descendant?

Stu

TOndrej

Have a look at TypInfo unit which contains utility functions to access RTTI (run-time type information). Delphi generates RTTI automatically (unless you turn it off with a compiler directive) for all published properties of any TPersistent descendant.
HTH
TOndrej

cubud

I think I know what you mean.

If you declare a property like this

property Images: TImageList read FImageList write FImageList;

In your code do this

if Assigned(Images) then
Images.Whatever;

Here are some tips !!

1) When you refer to an object, always check for the object being destroyed;

(In your component)
procedure Notification(AComponent: TComponent; Operation: TOperation); override;

Then....
procedure TMyComponent.Notification(AComponent: TComponent; Operation: TOperation); override;
begin
inherited;
if (Operation = opRemove) and (AComponent = FImages) then Images := nil;
end;

2) You are only notified of components on the same form being destroyed unless you specifically ask the component to notify you.

procedure SetImages(Value: TImageList);
property Images: TImageList read FImages write SetImages;

Then...
procedure TMyComponent.SetImages(Value: TImageList);
begin
if Assigned(Images) then Images.RemoveFreeNotification(Self);
FImages := Value;
if Assigned(Images) then Images.FreeNotification(Self);
end;

There are 2 component-writing articles on my web site www.HowToDoThings.com covering basics + properties of this sort.

http://www.howtodothings.com/showarticle.asp?article=310
and
http://www.howtodothings.com/showarticle.asp?article=320

Pete
====
http://www.HowToDoThings.com (Delphi articles)
http://www.Stuckindoors.com/delphi (Graphics, Sound, etc, open-source)

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ivobauer

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cubud

Yep, Ivo beat me on that one :)

But I still recommend reading those articles, especially as now part 3 has been added too !

http://www.howtodothings.com/showarticle.asp?article=327

Pete
====
http://www.HowToDoThings.com (Delphi articles)
http://www.Stuckindoors.com/delphi (Graphics, Sound, etc, open-source)

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