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if Assigned(Self.Edit) then Self.Edit.Text := 'Test';                    

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//...
type
  TLeseThread = class(TThread)
  private
    FSerial: TSerial;
  protected
    procedure Execute; override;
  public
    property Serial: TSerial read FSerial write FSerial;    
  end;

implementation

{ TLeseThread }

procedure TLeseThread.Execute;
var chr: char;
begin
  While not Terminated do  
    if Assigned(FSerial) then
      if FSerial.TryReadChar(chr) then
      begin
      end;
end;

end.                    

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Serial := ThreadKompo.Serial;
ThreadKompo.Serial := nil;
FreeAndNil(Serial);                    

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Type
    TThreadEx = class(TThread)
    Private
        {...}
        FSerial: TSerial;
        {...}
        function GetSerial: TSerial;
        procedure SetSerial(Const Value: TSerial);
        {...}
    Public
        {...}
        property Serial: TSerial Read GetSerial write SetSerial;
        {...}
    end;

{...}

procedure TThreadEx.SetSerial(Const Value: TSerial);
Begin
    If Not Assigned(Value) Then
    Begin
        //Finish the work with the Serial ...
    end;
    FSerial := Value;
end;

Function TThreadEx.GetSerial: TSerial;
begin
    Result := FSerial;
end;