How to make the same button run different code everytime it is clicked?

Question

I am currently doing a school project, I am making a Credit Card machine. I need the 'Enter Button' to run different code when it is clicked. The first click must get the card number from an edit ps... (I clear the edit once the card number has been retrieved), and the second click must get the pin from the same edit. How would I do this?

procedure TfrmMainMenu.btbtnEnterClick(Sender: TObject);

var

 sCvv,sPin:string;

begin

iCount2:=0;

sCardNumber:=lbledtCardInfo.Text;

if (Length(sCardNumber)<>16) AND (iCount2=0) then

 begin

    ShowMessage('Card number has to 16 digits,please try again!!');

  end

  else

  begin

  Inc(iCount2);

  lbledtCardInfo.clear;

  lbledtCardInfo.EditLabel.Caption:='Enter Pin' ;

  btbtnEnter.Enabled:=false;

  end; //if

  if iCount2=2 then

  begin

     btbtnEnter.Enabled:=true;

    sPin:=lbledtCardInfo.Text;

     ShowMessage(sPin);//returns a blank

  end;

Answer 1

You could try to do everything in a single event handler. There are several different ways to handle that. However, a different solution would be to use separate event handlers for each task, and then each task can assign a new handler for the next click to perform, eg:

procedure TfrmMainMenu.FormCreate(Sender: TObject);
begin
  // you can set this at design-time if desired...
  btbtnEnter.OnClick := GetCCNumber;
end;

procedure TfrmMainMenu.GetCCNumber(Sender: TObject);
begin
  sCardNumber := lbledtCardInfo.Text;
  if Length(sCardNumber) <> 16 then
  begin
    ShowMessage('Card number has to 16 digits,please try again!!');
    Exit;
  end;
  lbledtCardInfo.Clear;
  lbledtCardInfo.EditLabel.Caption := 'Enter Pin' ;
  btbtnEnter.OnClick := GetCCPin;
end;

procedure TfrmMainMenu.GetCCPin(Sender: TObject);
var
  sPin: string;
begin
  sPin := lbledtCardInfo.Text;
  if Length(sPin) <> 4 then
  begin
    ShowMessage('Card Pin has to 4 digits,please try again!!');
    Exit;
  end;
  ShowMessage(sPin);
  ...
  lbledtCardInfo.Clear;
  lbledtCardInfo.EditLabel.Caption := 'Enter Number' ;
  btbtnEnter.OnClick := GetCCNumber;
end;

A variation of this would be to create multiple buttons that overlap each other in the UI, and then you can toggle their Visible property back and forth as needed, eg:

procedure TfrmMainMenu.FormCreate(Sender: TObject);
begin
  // you can set this at design-time if desired...
  btbtnCCPinEnter.Visible := False;
  btbtnCCNumEnter.Visible := True;
end;

procedure TfrmMainMenu.btbtnCCNumEnterClick(Sender: TObject);
begin
  sCardNumber := lbledtCardInfo.Text;
  if Length(sCardNumber) <> 16 then
  begin
    ShowMessage('Card number has to 16 digits,please try again!!');
    Exit;
  end;
  lbledtCardInfo.Clear;
  lbledtCardInfo.EditLabel.Caption := 'Enter Pin' ;
  btbtnCCNumEnter.Visible := False;
  btbtnCCPinEnter.Visible := True;
end;

procedure TfrmMainMenu.btbtnCCPinEnterClick(Sender: TObject);
var
  sPin: string;
begin
  sPin := lbledtCardInfo.Text;
  if Length(sPin) <> 4 then
  begin
    ShowMessage('Card Pin has to 4 digits,please try again!!');
    Exit;
  end;
  ShowMessage(sPin);
  ...
  lbledtCardInfo.Clear;
  lbledtCardInfo.EditLabel.Caption := 'Enter Number' ;
  btbtnCCPinEnter.Visible := False;
  btbtnCCNumEnter.Visible := True;
end;