However, if we allow clipboard content in general, every user can also copy any other arbitrary non-numeric text into the field without our OnKeyPress event could prevent it. In the example above, keyboard shortcuts such as CTRL + V are rejected to, so that copying from clipboard will not work. One problem of this solution is that maybe users want to insert a number from clipboard. Additionally, we also allow VK_BACK (the backspace key) and VK_DELETE (the DEL key) so that the user still has the possibility to correct what he has typed. If not, we are setting Key to #0 by which the input is deleted and no longer takes place. We are doing that and as you can see in the code, we are checking whether Key is a digit from 0 to 9 or not in order to consider whether we want to disallow the input.

Therefore, we have enough time within this element to influence the user input before it is displayed. This event is triggered at each keypress in the Edit and passes the pressed key within the variable Key as Char even before the keystroke reaches the Edit.

procedure TForm1.Edit1KeyPress(Sender: TObject var Key: Char) The simplest method is to just use the OnKeyPress-Event of your Edit field. In this tutorial, I want to show you, how you can easily realize this behavior in Delphi or Lazarus. The user should only be allowed to type the digits 0 till 9 while letters or other characters should be rejected. Sometimes it may be necessary, that you only want numerical input in an Edit box.

Delphi numeric edit box in excel