Add a new property in TImage
lazarus / 31-LCL

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antoniocangiano76 · 2021-08-25 19:17

Hi,
I would like to know if it is possible to add a new property to a
TImage.
I need to add a property of type string called 'refer'  that i would
use like this:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i
image1.refer := 'pippo';Thanks

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antoniocangiano76 · 2021-08-25 19:27

A first thing I realized is that since Timage is created at runtime, I
have to add ExtCtrls to the uses.

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Soner · 2021-08-25 20:53

You can also take cdesim's code and put it in a library and use it
without installing it as component. You can still drop standard TImage
from componentpalette on your form and acces new property refer like
this:
First create unit:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i unit
myimage; {$mode objfpc}{$H+} interface uses Classes, ExtCtrls; type 
TMyImage = class(TImage)  private    FRefer: string;  protected 
public    property Refer: string read FRefer write FRefer; 
end; implementationend. 
Drop standard image to your form and use it normal and change in your
forms:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i unit
Unit1; {$mode objfpc}{$H+} interface uses  Classes, SysUtils, Forms,
Controls, Graphics, Dialogs, ExtCtrls, StdCtrls,  myimage; type 
TImage = class(myimage.TMyImage); //<-- ADD THIS   { TForm1 }   TForm1
= class(TForm)    Button1: TButton;    Image1: TImage;    procedure
Button1Click(Sender: TObject);    procedure FormCreate(Sender:
TObject);  private   public   end; var  Form1:
TForm1; implementation {$R *.lfm} { TForm1 } procedure
TForm1.FormCreate(Sender: TObject);begin  // LOOK at this: Image1 it
is TImage with new property  Image1.Refer:='Yes, It is TImage with
refer property';end; procedure TForm1.Button1Click(Sender:
TObject);begin  ShowMessage('Image1.Refer property
is:'+LineEnding+Image1.Refer);end; end. 
You can use TImage.Refer property only when you add at top of your
units this:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i uses
 myimage;type  TImage = class(myimage.TMyImage); //<-- ADD THIS 
I added example project.

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egsuh · 2021-08-26 02:28

Interposing (what Soner is suggesting) is appropriate if you need to
use it in many units of your project.

If you are going to use it only one unit, I'd rather recommend using
helpers. But here, if you need to add new fields, you cannot do it
with helpers. To add single field, you may use "tag" property to store
it.

If you need to add more than one field, interpose will be the option.

Currently I'm using interposing for many components, but all are
collected in one unit file, for a project group.

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antoniocangiano76 · 2021-08-26 06:02

Quote from: cdesim on August 25, 2021, 10:05:19 pmYou could create a
new class that descends from TImage

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i TMyImage =
class(TImage)  private    FRefer: string;  protected  public   
property Refer: string read FRefer write FRefer;end;
but then you could no longer simply drop it on a form from the
component pallet - you would have to create it in your code. I have
attached an example if you're interested.

Perfect!!! It was what I wanted. I don't need to drop it on a form
from the component pallet, I have to use in code.
Very thanks

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antoniocangiano76 · 2021-08-26 06:21

Quote from: jamie on August 25, 2021, 10:44:02 pmor simply use the TAG
property to point to a index of an array of string or constant.
Thank, I thought about it but I was looking for a solution that would
allow me to add n properties.
What if I wanted to add a method as well?

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egsuh · 2021-08-27 07:01

QuoteWhat if I wanted to add a method as well?
TMyImage is a inherited class, so you can do anything --- add new
methods, new fields, or override methods.