How to create a simple extended component and can change his
properties
lazarus / 31-LCL

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dcelso · 2013-02-25 08:35

How to create a simple extended component and can change his
properties in Objec Inspector?

Hello, i'm trying create a custom label with an aditional property.
To do it i tryied create a new package, use TLabel as parent, add a
publised property

property mynewprop : integer read fmynewprop write setmynewprop;

creating a private fmynewprop integer atribute, and a private
procedure setmynewprop(newval : integer)

I compile the package, the Tmylabel appears, but I cant see the new
property in object inspector.

What I need more?

Thanks.

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taazz · 2013-02-25 08:42

nothing. The property should be visible on inspector as long as you
have your label selected on the form designer.

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dcelso · 2013-02-27 11:34

Thanks, it work well only with basics types, integer, string, etc.
But now I'm trying to do it with a custom class, and I can not select
it in object inspector, like tshelllistview do with tshelltreeview,
for example.

property mynewprop : TMyClass read fmynewprop write setmynewprop;

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Blaazen · 2013-02-27 11:45

Your class must be derived from TComponent TPersistent. Also, you have
to call "SetSubComponent(True);" in constructor.
Code: [Select]constructor TMainComp.Create(AOwner: TComponent);
begin
  inherited Create(AOwner);
  FSubComp:=TSubComp.Create(self);
  with FSubComp do
    SetSubComponent(True);
end;
EDIT: I correct myself. TPersistent is enough (for streaming)

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dcelso · 2013-03-01 07:26

It not compile, sais
 wrong number of parameters specified for call create
and
 identifier fsubcomp not found.

I trye with create without parameters to solve the first problem but
the second problem continues.

My two class to do an example are the nexts:
Code: [Select]unit umylabel;

{$mode objfpc}{$H+}

interface

uses
  Classes, SysUtils,StdCtrls;

type
  TMyLabel= class(TLabel)
  private
    { private declarations }
    fmycustomclass: TCustomClass ;
  public
    { public declarations }
  published
    property mycustomclass :TCustomClass read fmycustomclass write
fmycustomclass;
  end;

implementation

end.   
Code: [Select]unit uMyCustomClass;

{$mode objfpc}{$H+}

interface

uses
  Classes, SysUtils;


type
  TCustomClass= class(TPersistent)
  private
    { private declarations }
  public
    { public declarations }
    constructor Create(AOwner: TComponent);
  end;

implementation

constructor TCustomClass.Create(AOwner: TComponent);
begin
  inherited Create(AOwner);
  FSubComp:=TSubComp.Create(self);
  with FSubComp do
    SetSubComponent(True);
end;

end.

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taazz · 2013-03-01 07:59

The TPersistent create constructor does not support the owner
construct at all. It is not a component so it can not be used as the
owner of a component what is the subcomponent type? Declaring an empty
property of type TMylabel inside your TMyLabel class is at least
questionable the fact that you do not give it any value leaving it at
nil will of course  prevents Object inspector from showing any
properties that class might have but you should be able to see the
property myLabel on the inspector none the less as long as you have
installed it in the IDE.

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dcelso · 2013-03-01 12:54

Thansk for the response, I don't want do it. My example was wrong.

I want do the same as tshellistview do with tshelltreeview, where you
put a tshelllistview you can indicate in a property what object of
tshelltreeview want use in it.

I want do the same but Tmylabel and tmycustomclass.

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dcelso · 2013-03-01 12:57

The other thing, is a litle stupid

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Blaazen · 2013-03-01 13:18

@ dcelso
Sorry for confusion. I quickly looked to my sources wrote the short
snippet above.
Subclass definitely can be TPersistentand appears in OI but in my code
(TSubClass), I declared my own property Parent and my own constructor
Create(AParent: TComponent);
The reason is that I needed access to main component from
subcomponent.
And of course, because TPersistent has no owner, you have to free it
manually in destructor of the main class.

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taazz · 2013-03-01 13:19

It is not recomended to use the TPersistent in that way there are a
lot of things that it does not support that will bring the ide to its
knees as an example TPersistent does not support the free notification
mechanism making impossible to know when the external component is
destroyed leaving your component in an unstable state. There is also
the problem of the property editor that needs to defined or written in
order to allow the end user to select only your specific class which
of course is unknown to the IDE.

If you want to do such an elaborate linking between your component and
some other 3rd one, then you need to make sure that both of them are
inherited from at least TComponent to make your life easier with the
IDE integration.

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dcelso · 2013-03-01 19:38

Thanks. But i dont undertand how chage my ucustomclass to solve it,
yet. .
I ve deleted the parameter of constructor but it continues doing
errors.
I ve changed tpersistern to tcomponent with sames results.
Deleting constructor. It compiles. But when i install the package and
i use my tmylabel i dont see in object inspector the property
mycustomclass to select an object.  Like tshelllistview do with
tshelltreeview.

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Blaazen · 2013-03-01 20:30

I attached a very simple component LabelX with SubClass(TPersistent)
which appears in OI - I tested  .

EDIT: Oops, everything works, it appears in OI, I only forgot to free
subcomponent. However, it is easy to fix, I will not upload new
version.
You can: add destructor TLabelX.Destroy and call SubClass.Free there
OR change SubClass from TPersistent to TComponent and set owner. Owner
will care.

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dcelso · 2013-03-02 12:05

Thanks, I'll study it.
But I 've discovered that an application with custom visual
components, is more dificult to mantain that other that use the
commons lazarus components and adding the needed things manually.

Because if you change of computer you need donload lazarus, compile
package, install package on ide and recompile it (to can see it on
palette and objtect inspector), compile project, then you can start to
write code etc. If you use same units in your package and in your
project, lazarus does not do to you compile together, it sais that you
are using in your project and is not recomended add it to you package,
but it does not leave to you do it.

And If you have all without packages you only need run lazarus and
start to write code .

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Blaazen · 2013-03-02 12:15

QuoteBecause if you change of computer you need donload lazarus,
compile package, install package on ide and recompile it (to can see
it on palette and objtect inspector), compile project, then you can
start to write code etc. If you use same units in your package and in
your project, lazarus does not do to you compile together, it sais
that you are using in your project and is not recomended add it to you
package, but it does not leave to you do it.
Hmm, I can imagine that this is problem in school where is many
computers and you sit everytime elsewhere. So you need install
Laz.+components to every machine.

I work with only one PC and recompiling Laz. or adding new component
is done in acceptable time.
When I do only a small change in component which is already installed,
rebuilding IDE is a few seconds.

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dcelso · 2013-03-02 12:34

Quote from: Blaazen on March 02, 2013, 01:15:41 pmQuoteBecause if you
change of computer you need donload lazarus, compile package, install
package on ide and recompile it (to can see it on palette and objtect
inspector), compile project, then you can start to write code etc. If
you use same units in your package and in your project, lazarus does
not do to you compile together, it sais that you are using in your
project and is not recomended add it to you package, but it does not
leave to you do it.
Hmm, I can imagine that this is problem in school where is many
computers and you sit everytime elsewhere. So you need install
Laz.+components to every machine.
Exactly. .

In other hand,  I saw you example, , It's a great example, I love it,
I will use this method to another project that I have.I have a
question related with it, is it not necessary to create the destructor
to free the tsubcomponet? How free it currently.

But it is not that Im searching in this thread. I'm searching the
interconection of two visual components, like, I insist,
tshelllistview do with tshelltreeview. When you Drop a tshelllistview
to your form in a property called shelltreeview you can select an
object of this tipe, for example you can drop to your project three
tshelltreeviews, and in your shelllistview1.shelltreeview property you
can see shelltreeview1,shelltreeview2 and shelltreeview3 to select one
of this.
So the control of create or destroy they have the application, instead
of your custom visual component (as your example, tlabelx, do)

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dcelso · 2013-03-03 23:29

Quote from: dcelso on March 02, 2013, 01:34:20 pm....
But it is not that Im searching in this thread. I'm searching the
interconection of two visual components, like, I insist,
tshelllistview do with tshelltreeview. When you Drop a tshelllistview
to your form in a property called shelltreeview you can select an
object of this tipe, for example you can drop to your project three
tshelltreeviews, and in your shelllistview1.shelltreeview property you
can see shelltreeview1,shelltreeview2 and shelltreeview3 to select one
of this.
...
Anyone knows how to do it?

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Blaazen · 2013-03-03 23:58

I am not sure that I perfectly understand. TShellTreeView is just for
browsing files. If you want to browse different paths in one
ShellTreeView, you can only change its "root" property. It can be done
in many ways. You can use TTabControl, TComboBox, Buttons etc. There's
no need to create new component.

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dcelso · 2013-03-04 00:25

Don't
tshelllistview have a property called shelltreeview, this property can
be changed in object inspector in design time, to select an object of
tshelltreeview type. At press in this property in object inspector a
combobox open a list of all of yours objects of this type have in your
project to selec one. for example if you drop two tshelltreeview from
the components palette to your form, you will have two objects of
tshelltreeview, shelltreeview1 and shelltreeview2, and those names You
will see when you try to change the shelltreeview propertry of your
shelllistview1 in the object inspector.
This kind of interconection of objects Is that I`m trying to simulate.

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dcelso · 2013-03-06 18:01

, I done it. I'm the best 
You only need extend of TComponent your two classes. And register they
in the component palette. And automatically you can interconect they
as tshellistview and tshelltreeview do.

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dcelso · 2013-03-06 18:29

But now, I don`t do it circular.
I have a tmyedit and a tmylabel, and tmyedit have a porperty called
mylabel that you can select an object of tmylabel dropped from
palette.

I'm trying to do now the same in tmylabel,ie, a property called myedit
that you can select and object of tmyedit. But when it add umylabel
unit lazarus sais that there is a circular reference beteen umyedit an
umylabel, and it does not compile.

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JuhaManninen · 2013-03-06 18:42

Quote from: dcelso on March 06, 2013, 07:29:30 pmI'm trying to do now
the same in tmylabel,ie, a property called myedit that you can select
and object of tmyedit. But when it add umylabel unit lazarus sais that
there is a circular reference beteen umyedit an umylabel, and it does
not compile.

In that case the cross-reference really must be in the interface part.
The only solution is to copy the components into one unit.
LCL has the same problem with many components. The code is divided
into smaller files by using include files for the implementation part.
Lazarus IDE fully understands and supports include files.

About the original problem:
The best way to know how a certain component works, is to look at its
source code. This is open source after all.
Just Ctrl-Click TShelLlistView or TShellTreeView and you are taken to
its sources. Maybe you did just that, I don't know.

Juha