please make some procedures virtual; suggestion for a new tForm
event/procedure
lazarus / 7-LCL

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Martin V · 2010-01-31 22:43

Hi,

I am a Lazarus beginner and have got only a few modifications for the
LCL/FPC yet. Later, I will get part of the development community, but
at the moment, I would prefer that someone takes a look at my
proposals and makes the changes.


forms.pas

declaration of class tForm:
    procedure Close; -> should be virtual to enable overriding
    procedure Show;  -> should be virtual to enable overriding
   
controls.pas

declaration of class tControl

    move from private to protected:
      procedure SetFont(Value: TFont) -> should be virtual to enable
overriding
   

classesh.inc (fpc rtl)
declaration of class tList:
    procedure Delete -> should be virtual to enable overriding
   
--------------------------

proposal for a new tForm event:

In WDsibyl, there's a useful Form procedure / Form event which is not
part of Lazarus and Delphi: SetupShow/OnSetupShow

The SetupShow has to be executed the first time when the Form is
shown. boolean "IsFirstShow" has to be set to true in Create.

procedure tSibylForm.Show;
  begin
    if IsFirstShow then SetupShow;
    IsFirstShow := false;
    inherited Show;
  end;
 
This would be a useful feature for lots of Lazarus (Delphi) users,
because when overriding the Create constructor, a lot of stuff (e.g.
Window handles) is not initialized yet and a lot of initialization
stuff fails there. Lots of programmers have to override Show and need
to write this simple code again and again...

In WDsibyl, there's also a SetupComponent procedure and an
OnSetupComponent event which is more handy than overriding the
constructor. Would be nice to have, but the OnSetupComponent is nearly
the same as OnCreate.


Martin V. (Munich, Germany)

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theo · 2010-01-31 23:13

Quote from: Martin V on January 31, 2010, 11:43:04 pm    procedure
Close; -> should be virtual to enable overriding
    procedure Show;  -> should be virtual to enable overriding
   
I don't know exactly what you need, but are you aware that you can
override DoClose and DoShow?

Quote from: Martin V on January 31, 2010, 11:43:04 pm    move from
private to protected:
      procedure SetFont(Value: TFont) -> should be virtual to enable
overriding
   
Again, not sure about the purpose.
There is an event TFont.OnChange where you can get notified about
changes.
   
Quote from: Martin V on January 31, 2010, 11:43:04 pmclassesh.inc (fpc
rtl)
declaration of class tList:
    procedure Delete -> should be virtual to enable overriding
       
This is one for the Freepascal Mailinglist:
http://www.freepascal.org/maillist.var

Quote from: Martin V on January 31, 2010, 11:43:04
pmSetupShow/OnSetupShow
       

Good idea imho.

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Ñuño_Martínez · 2010-02-01 09:33

Completely agree with Theo. But I must add: Why do you use the word
should? I think it's a big word. May be you should use may, shouldn't
you?

As for the TList modification:
Quote from: Martin Vclassesh.inc (fpc rtl)
declaration of class tList:
    procedure Delete -> should be virtual to enable overriding
Why?

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Martin V · 2010-02-01 14:47

Quote from: theo on February 01, 2010, 12:13:06 am  
I don't know exactly what you need, but are you aware that you can
override DoClose and DoShow?

>procedure SetFont(Value: TFont) -> should be virtual to enable
overriding
Again, not sure about the purpose.
There is an event TFont.OnChange where you can get notified about
changes.

Thanks for your response. I indeed did not notice DoShow and DoClose,
this should fit my purpose.

I thaught that the only purpose of On... Events is to use it in the
object inspector for forms which are a visual resource. Can I
overwrite On... in Lazarus when overriding a class?
   
Quote from: Martin V on January 31, 2010, 11:43:04 pmclassesh.inc (fpc
rtl)
declaration of class tList:
    procedure Delete -> should be virtual to enable overriding

I have got a list of pointers pointing to heap objects. If the list
item gets deleted, the pointer has to be freed. So I need to have a
"FreeItem (Item : pointer)" where I can place my code to free the
heap. But perhaps there's another way without modifying the RTL ?
       
Martin V. (Munich, Germany)

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theo · 2010-02-01 14:57

Quote from: Martin V on February 01, 2010, 03:47:32 pmI thaught that
the only purpose of On... Events is to use it in the object inspector
for forms which are a visual resource. Can I overwrite On... in
Lazarus when overriding a class?

You can use On.. in your code like:
MyObj.OnShow:=@Eventhandler;

Or you have something like DoShow which actually triggers OnShow if
assigned and which you can override.
   
Quote from: Martin V on January 31, 2010, 11:43:04 pmBut perhaps
there's another way without modifying the RTL ?

Maybe TObjectList. It has a property OwnsObjects. See
http://www.freepascal.org/docs-html/fcl/contnrs/tobjectlist.html

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Ñuño_Martínez · 2010-02-01 15:12

Quote from: Martin V on February 01, 2010, 03:47:32 pmI have got a
list of pointers pointing to heap objects. If the list item gets
deleted, the pointer has to be freed. So I need to have a "FreeItem
(Item : pointer)" where I can place my code to free the heap. But
perhaps there's another way without modifying the RTL ?
If you need a list of Objects then use TObjectList or TFPObjectList
instead. They're very similar than TList but they destroy the objects
by default.