Thread and Callback

unit Unit4;

interface

uses
  System.SysUtils, System.Types, System.UITypes, System.Classes, System.Variants,
  FMX.Types, FMX.Controls, FMX.Forms, FMX.Graphics, FMX.Dialogs, FMX.StdCtrls,
  FMX.Controls.Presentation, FMX.ScrollBox, FMX.Memo;

type
  TUpdate = procedure (const text: string) of object;
  TDemo = class
  private
    fUpdate: TUpdate;
  public
    constructor Create (const aUpdate: TUpdate);
  end;

  TForm4 = class(TForm)
    Memo1: TMemo;
    Button1: TButton;
    procedure FormDestroy(Sender: TObject);
    procedure Button1Click(Sender: TObject);
  private
    fDemo: TDemo;
    procedure update (const text: string);
  public
    { Public declarations }
  end;

var
  Form4: TForm4;

implementation

uses
	System.Threading;

{$R *.fmx}

{ TDemo }

constructor TDemo.Create (const aUpdate: TUpdate);
var
  dbTask: ITask;
  dbTaskArray: array [0..0] of ITask;
begin
  fUpdate:=aUpdate;
  dbTask:=TTask.Create(
                        procedure
                        var
                          i: Integer;
                        begin
                          for i := 0 to 10 do
                          begin
                            TThread.Queue(nil,
                                      procedure
                                      begin
                                        fUpdate(I.ToString);
                                      end);
                          end;
                        end
                      );
  dbTaskArray[0]:=dbTask;
  dbTask.Start;
  TTask.WaitForAll(dbTaskArray);
end;

procedure TForm4.FormDestroy(Sender: TObject);
begin
  fDemo.Free;
end;

procedure TForm4.Button1Click(Sender: TObject);
begin
  fDemo:=TDemo.Create (update);
end;


procedure TForm4.update(const text: string);
begin
  Memo1.Text:=text+sLineBreak+Memo1.Text;
end;

end.

Try this

constructor TDemo.Create(const aUpdate: TUpdateProc);
var
  dbTask: ITask;
begin
  FUpdateProc := aUpdate;
  dbTask := TTask.Create(procedure
    begin
      TParallel.For(0, 10, procedure(Arg1: Integer)
        begin
          TThread.Queue(nil, procedure
            begin
              FUpdateProc(Arg1.ToString);
            end);

        end)
    end);

  dbTask.Start;
  dbTask.Wait;
end;