Initial value of a property in a component

[panoss]

I'm making a control using TCustomControl:

Code: Pascal  [Select][+][-]

1. constructor myCustomControl.Create(AOwner: TComponent);
2. begin
3.    inherited Create(AOwner);
4.    FAlpha := 255;    
5. end;
6.  

The problem is that when the component is created (when I run it), FAlpha does not take the value 255, but the value 0. Why? What should I do?

FAlpha is used in Get an Set of property Alpha:

Code: Pascal  [Select][+][-]

1. function myCustomControl.GetAlpha: byte;
2. begin
3.       Result := FAlpha;
4. end;
5. procedure myCustomControl.SetAlpha(newAlpha: byte);
6. begin      
7.       FAlpha := newAlpha;          
8. end;
9.  

[eny]

Did you override your custom constructor?

Code: Delphi  [Select][+][-]

1.   TmyCustomControl = class(... <your parent class>)
2.     //...
3.     constructor Create(TheOwner: TComponent); override;
4.     //...
5.  

 

[panoss]

Yes I have overriden it.

[eny]

Did you create a package for the component? I.e. it was added to the component palette?
Or do you create the component at runtime?
If it's the latter, the property will have the correct value immediately after the constructor is called.

[panoss]

Yes I have created a package for the component and installed it. It's been added at the components palette.

[eny]

Did a small test: simple custom component, descendant of TcustomControl and added it to a package.
Added a custom constructor to set a local property and that all worked perfectly!
This is for Window$ though and a fairly recent Lazarus/FPC version (see my sig).

[panoss]

Thank you for bothering.
I haven't found why this is happening to me.
May be it's the version of FPC or Lazarus I'm using.

[Marc]

this is not fpc/lazarus version dependent.
Somehow your package is not installed. or not used.

How doe you conclude it didn't get the initial value ?

[panoss]

As I mentioned on the other topic ( ), I can't make the debugger work properly.
So, in the Setter of the property, and in the MouseDown event,
I've put a line: ShowMessage('A=' + IntToStr(FAlpha));
which shows me the value every time the SetAlpha is called, or MouseDown raised.

[panoss]

When I Run the application, firstly is being executed the Constructor.
FAlpha takes the value 255.
BUT, after that is executed the Setter (automatically, I don't call it), where FAlpha := newAlpha;
And newAlpha = 0, so and FAlpha = 0.

I think I will declare newAlpha at the Private section of the component (now it's declared in the Setter, see 1st post), and give it the value I want in the constructor.
Is this the correct way? Any better suggestion?

[Laksen]

Remember that components are streamed, so published properties will be set to the value they are given at design time. That would explain why the setter is called after Create

You cannot avoid this behavior for visually/streamed created components, unless you make the property non-published

[panoss]

Laksen, you were correct!! I moved the property from published to public, and everything works as expected (ok , I had to press the 'install' button in the package manager,for the package to be reinstalled, and replace the existing component from my test form with a new one).
Works fine!!Thank you!

[eny]

Laksen, you were correct!! I moved the property from published to public, and everything works as expected

Things don't work as expected: they work as designed.
Maybe that was the problem.

[panoss]

Ok, you are correct .
But how could I know how they are designed?

[eny]

Ok, you are correct .
But how could I know how they are designed?

The 'problem' lies in the 'expecting'