What I’m trying to achieve, in simplified form, is to create a list of dynamically created buttons. When clicking on one of the buttons it should be removed from the list and its object should be freed. My approach is :
Create a TList<TButton>
Create a couple of TButton objects and add them to the TList<TButton>
Assign the Form as the Parent for each of the created TButton objects
Assign a Position for each of the created TButton objects
Assign an OnClick handler method to each of the created TButton objects
The OnClick handler sets the Sender TButton’s Parent to nil and deletes it from the TList<TButton>, so that ARC can free the TButton object that was clicked on.
When I click on one of the dynamically created buttons, I get a “Segmentation Fault”. I suspect it is because I am freeing the TButton object in its own OnClick handler and the class is trying to do some other stuff with it after my handler.
I have tested this on Android. I assume the same will happen on iOS, or any other ARC platform for that matter.
Is there a better/right way to do this, or another approach I should be following to get it working the way I want?
Here is some example code. It is for a form with one design-time button (Button1) on it. Clicking this button repeatedly dynamically creates new buttons and adds them to the list.
unit Unit2;
interface
uses
System.SysUtils, System.Types, System.UITypes, System.Classes, System.Variants,
FMX.Types, FMX.Controls, FMX.Forms, FMX.Graphics, FMX.Dialogs,
FMX.Controls.Presentation, FMX.StdCtrls, System.Generics.Collections;
type
TForm2 = class(TForm)
Button1: TButton;
procedure Button1Click(Sender: TObject);
procedure FormCreate(Sender: TObject);
private
ButtonList : TList<TButton>;
procedure ButtonClick(Sender: TObject);
{ Private declarations }
public
{ Public declarations }
end;
var
Form2: TForm2;
implementation
{$R *.fmx}
procedure TForm2.ButtonClick(Sender: TObject);
var
pos : Integer;
begin
pos := ButtonList.IndexOf(TButton(Sender));
TButton(Sender).Parent := nil;
ButtonList.Delete(pos);
end;
procedure TForm2.FormCreate(Sender: TObject);
begin
ButtonList := TList<TButton>.Create;
end;
procedure TForm2.Button1Click(Sender: TObject);
var
pos : Integer;
begin
pos := ButtonList.Add(TButton.Create(nil));
ButtonList.Items[pos].Parent := Form2;
ButtonList.Items[pos].Position.Y := 50 * ButtonList.Count;
ButtonList.Items[pos].OnClick := ButtonClick;
end;
end.
