Delete TLabel in Delphi

Question

I currently create a two TLabels and a TEdit dynamically, naming them LblDesc+i, EdtAmount+i and LblUnit+i - Where i is an integer that I iterate up by one each time I add those 3 elements. The data in the elements are just for simulation purposes. My problem now is deleting the three objects. Ive tried with free and FreeAndNil, no luck at all. Any help is greatly appreciated.

procedure TForm1.BtnAddClick(Sender: TObject);
begin
  LblDesc := TLabel.Create(Self);
  LblDesc.Caption := 'Item '+IntToStr(i);
  LblDesc.Name := 'LblDesc'+IntToStr(i);
  LblDesc.Left := 16;
  LblDesc.Top := 30 + i*30;
  LblDesc.Width := 100;
  LblDesc.Height := 25;
  LblDesc.Parent := Self;

  EdtAmount := TEdit.Create(Self);
  EdtAmount.Text := IntToStr(i);
  EdtAmount.Name := 'EdtAmount'+IntToStr(i);
  EdtAmount.Left := 105;
  EdtAmount.Top := 27 + i*30;
  EdtAmount.Width := 60;
  EdtAmount.Height := 25;
  EdtAmount.Parent := Self;

  LblUnit := TLabel.Create(Self);
  LblUnit.Caption := 'Kg';
  LblUnit.Name := 'LblUnit'+IntToStr(i);
  LblUnit.Left := 170;
  LblUnit.Top := 30 + i*30;
  LblUnit.Width := 50;
  LblUnit.Height := 25;
  LblUnit.Parent := Self;

  i := i+1;
end;

procedure TForm1.BtnRemoveClick(Sender: TObject);
begin
  //Delete

end;

What do you mean by "no luck"? What happens/doesn't happen? Anyway you need to show the code that you're actually trying to use to remove the components. — MartynA, Feb 17 '16 at 10:39
Welcome to StackOverflow. Please show how exactly you tried to delete these controls. In any case, you could either keep the references of created controls, or retrieve them by name with [`FindComponent`](http://docwiki.embarcadero.com/Libraries/XE7/en/System.Classes.TComponent.FindComponent) later. — Free Consulting, Feb 17 '16 at 10:41
I reverted your last edit. If you want to show the code that ended up working, post it as an answer in the space below (headed *Your Answer*) where it belongs. Answering your own question is totally acceptable here. — Ken White, Feb 17 '16 at 13:49

fantaghirocco · Accepted Answer · 2016-02-17T14:29:17.183

4

In the past I had issues related to the deletion of some component that I've solved setting the parent's component to nil but it should be no longer the case since TControl's destructor - if called - already does the job.

The component should be removed by simply freeing it.

LblUnit.Free;

If you need to find the component by its name, use System.Classes.TComponent.FindComponent or iterate on the Components list.

for i := ComponentCount-1 downto 0 do begin
  if Components[i].Name = 'LblUnit'+IntToStr(i) then begin
    //TControl(Components[i]).Parent := nil; {uncomment if you have the same issue I've had}
    Components[i].Free;
  end;
  . . .  
end;

EDIT

If the index i used for the component's name construction 'LblUnit'+IntToStr(i) doesn't lie in the range [0..ComponentCount-1], the index has to be modified accordingly.

edited Feb 17 '16 at 14:29

answered Feb 17 '16 at 10:48

fantaghirocco

4,761
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This Ive tried, the problem is it never finds the component. When debugging, it cycles through components and never finds it. – H4rdstyler Feb 17 '16 at 11:36
maybe the `i` in the `BtnAddClick` is greater than `ComponentCount-1` – fantaghirocco Feb 17 '16 at 11:44
The debugger on Componenets[j].Name says: "Components = '[' expected, but end of file found. The i starts at 1 when the first component is added. – H4rdstyler Feb 17 '16 at 11:46
the above compiles fine for me on XE4 – fantaghirocco Feb 17 '16 at 11:50
It complies fine, it just doesnt find the component. – H4rdstyler Feb 17 '16 at 11:53
start `i` with `0` or use `1+i` where `i` appears between the `begin end` block in my code – fantaghirocco Feb 17 '16 at 11:59
If I replace "Components[j].Name = 'LblDesc'+IntToStr(i)" with "Components[j].Name = 'LblDesc2'" - It removes the 2nd label just fine – H4rdstyler Feb 17 '16 at 12:07
`i` and `j` are different variables :-s – fantaghirocco Feb 17 '16 at 12:10
They are both Integers. When the debugger reaches j=4 and i=4 (which it does when cycling through), it does nothing. – H4rdstyler Feb 17 '16 at 12:12
@TomBrunberg *What makes you think...* -> in a comment the OP states that his `i` starts with `1` and in his code `i := i+1` so it was my - maybe wrong - assumption. I've already warned the OP about the value of `i` in a previous comment – fantaghirocco Feb 17 '16 at 12:45
I found the error and corrected it. The code mentioned above works. EOD. – H4rdstyler Feb 17 '16 at 12:52
@TomBrunberg That's what I meant with [this comment](http://stackoverflow.com/questions/35454111/delete-tlabel-in-delphi/35454492#comment58607929_35454492). The OP can do something like `if Components[5+i].Name`: only the OP knows – fantaghirocco Feb 17 '16 at 12:52
@TomBrunberg agree, I'm going to edit with the tip. Thank you – fantaghirocco Feb 17 '16 at 13:05
"Set the component's Parent property to nil before freeing it." Could you explain why this is needed? – Kromster Feb 17 '16 at 13:50
@KromStern there's no need indeed: `TControl`'s destructor already sets the `Parent` to `nil`. I had issues related to that long time ago and I've maintained this practice – fantaghirocco Feb 17 '16 at 14:05
Could you change your answer accordingly? Thanks – Kromster Feb 17 '16 at 14:09
@Krom and @@Tom ok, so you guys can stop kicking my ass - for today at least :D – fantaghirocco Feb 17 '16 at 14:27

score 0 · Answer 2 · answered Feb 17 '16 at 10:53

To delete dynamically created component, you must have valid reference to it.

You can organize own array or list to keep your objects, or use existing lists, for example - Form.Components[] which holds objects whose owner is Form.

In the second case you have to find needed objects with FindComponent by name or walk through Components[] and search for component with some feature (Name, class type, Tag etc)

score 0 · Answer 3 · answered Feb 17 '16 at 14:19

0

The answer that ended up working was this:

procedure TForm1.BtnRemoveClick(Sender: TObject);
var
  j: Integer;

begin
  for j := ComponentCount-1 downto 0 do begin
    if Components[j].Name = 'LblDesc'+IntToStr(i-1) then begin
      TControl(Components[j]).Parent := nil;
      Components[j].Free;
    end;
  end;
end;

answered Feb 17 '16 at 14:19

H4rdstyler

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1

There is no need to set Parent to nil – MBo Feb 17 '16 at 16:46
You are better off keeping your own array/list of labels that you create, and then you can loop through that when needed. You *can* use the `Owner`'s `Components[]` property or the `Parent`'s `Controls[]` property to manage that for you, but it is overkill considering that other controls are also in those same lists. Better to isolate your desired controls in their own list, your code will be cleaner and safer for it. – Remy Lebeau Feb 17 '16 at 18:21

Delete TLabel in Delphi

3 Answers3