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Design time compoment problem

I have a component decended from TComponent (Component A). One of its published properties is another component (Component B). At design time I can select a component from the form for this property in the object inspector.

The problem is this:

When I delete Component B from the form, the refernce remains in Component A. This upsets Delphi enormously and causes all sorts of access violations. I cannot alter the code for Component B (it could be a VCL object for example) so what is the correct solution for this problem.

Somehow when Component B is deleted, Component A must Nil its reference. Perhaps I should listen for a message in Component A? if so which one? Maybe there is something I can do with csDesigning flag? Any ideas?

An Example :

type
TComponentA = class(TComponent)
private
fComponentB : TComponent;
published
property ComponentB : TComponent read fComponentB write fComponentB ;
end;

ASKER CERTIFIED SOLUTION

kretzschmar

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StevenB

ASKER

brilliant, so the solution is this:

type
TComponentA = class(TComponent)
private
fComponentB : TComponent;
protected
procedure Notification(AComponent: TComponent; Operation: TOperation); override;
published
property ComponentB : TComponent read fComponentB write fComponentB ;
end;

procedure TEntSMSTextMessageEdit.Notification(AComponent: TComponent; Operation: TOperation);
begin
If (AComponent = fComponentB) and (Operation = opRemove) then fComponentB := Nil;
end;

Thanks meikl, fastest solution ever :o)

Steven

StevenB

ASKER

or rather ...

procedure TComponentA.Notification(AComponent: TComponent; Operation: TOperation);
begin
If (AComponent = fComponentB) and (Operation = opRemove) then fComponentB := Nil;
end;

;o)

kretzschmar

well, glad to helped you,
sorry that i didn't had the correct syntax in mind,
(have no delphi available at the moment)

but as i see, you get it work

good luck again

meikl ;-)