Question

Currently when i click on a button it will create some shapes on a new form. Once i close the new form how can i destroy the shapes it made.

I can add more info if needed but was hopeing there was a simple way to destroy all TMachine instances when the form closed.

TMachine is a TShape Class

procedure TFLayout1.GetClick(Sender: TObject);
var
  azone: string;
  adept: string;
  machine : TMachine;
begin
  fdb.count := 0;  //keeps track of number of machines in zone
  azone := MyDataModule.fDB.GetZone(Name);    //gets name of zone
  adept := TButton(Sender).Name;       //gets name of dept
  fdeptlayout.ListBox1.Clear;

  fdeptlayout.show;
  with fdeptlayout.ADOQuery1 do
    begin
         sql.Clear;
         sql.BeginUpdate;
         sql.Add('SELECT');
         sql.Add(' *');
         sql.Add('FROM');
         sql.Add(' `MList`');
         sql.Add('WHERE `Zone` = :myzone ');
         sql.Add(' AND `Dept` = :mydept');
         sql.EndUpdate;

         parameters.ParamByName('myzone').Value := azone;
         parameters.ParamByName('mydept').Value := adept;
         open;
    end;

  //gets number of machines in total
  while not fdeptlayout.ADOQuery1.Eof do
    begin
      fdb.count := fdb.count+1;
      fdeptlayout.ADOQuery1.Next;
    end;

  //restarts back at first query
  fdeptlayout.ADOQuery1.First;

   //clears the last x value
   fdb.LastX :=0;

  //creates the shape
  while not fdeptlayout.ADOQuery1.Eof do
    begin
        machine := MachineShape.TMachine.Create(self);
        machine.Parent := fdeptlayout;
        machine.PlaceShape(44,44,'CM402','first','123/33/123');
        fdeptlayout.ListBox1.Items.Add(fdeptlayout.ADOQuery1.FieldByName('Name').AsString);
        fdeptlayout.ADOQuery1.Next;
    end;
end;

TMachine Class

unit MachineShape;


interface

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, extctrls,myDataModule,Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls;

type

TMachine = class(TShape)
  private
    { Private declarations }
  public
    { Public declarations }
    procedure PlaceShape(sizeW,sizeH :integer; name, order,asset : string);
  end;
implementation



    Procedure TMachine.PlaceShape(sizeW,sizeH :integer; name, order,asset : string);
    begin
       self.width :=  sizeW;
       self.height := sizeH;
       self.top := 136;
       self.left := MyDataModule.fDB.LastX +2;//set left
       MyDataModule.fDB.lastx := left + sizeW;
       showmessage(inttostr(mydatamodule.fDB.LastX));
    end;

end.

FDeptLayout

unit DeptLayout;

interface

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls,mydatamodule, Vcl.Forms, Vcl.Dialogs, Data.DB, Data.Win.ADODB, Vcl.StdCtrls,
  Vcl.ExtCtrls;

type
  TfDeptLayout = class(TForm)
    ADOQuery1: TADOQuery;
    ListBox1: TListBox;
    procedure FormClose(Sender: TObject; var Action: TCloseAction);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  fDeptLayout: TfDeptLayout;

implementation

{$R *.dfm}

procedure TfDeptLayout.FormClose(Sender: TObject; var Action: TCloseAction);
begin

end;

end.

Answer 1

The shown code is taking advantage of the VCL ownership model and the form will free it for you, as you just pass the form itself as the owner of your components when you create it:

machine := MachineShape.TMachine.Create(self);

as this is called from the TFLayout1 class, when the particular instance of the form is destroying itself, it will free all the owned components.

For a little more info, you can read the article: Owner vs. Parent in Delphi.

Edit

From comments, it resulted you create the TMachine instances on a class different of the form on which you show it, and you don’t destroy the form instance when you close it, so, you can reach what you want making this changes:

• Make the form in which the shapes are shown the owner, changing your code to create them to this:

  //don't use self, now the parent is the instance referenced by fdeptlayout
  machine := MachineShape.TMachine.Create(fdeptlayout);
  

• On your Tfdeptlayout class, add a OnClose handler with this code:

  begin
    for I := ComponentCount - 1 downto 0 do
      if Components[I] is TMachine then
        Components[I].Free;
  end;
  

That said, you really have to read the documentation and referenced articles to gain some understanding of what’s going on behind the scenes in your Delphi application.