key down

Overview

The OnKeyDown event of an object allows you to check what key the user has pressed.

Note that the procedure keeps track of shift/alt/ctrl etc keys separately (in Shift) from the "regular" keys (in Key) - see the procedure signature in the example.

Note: OnKeyDown doesn't support Unicode characters. If you need Unicode characters but no control characters, use OnUTF8KeyPress.

Note: When a key is held down, the OnKeyDown event is re-triggered. The first re-triggering event is after approx 500 ms and the next ones cycle between 30 and 50 ms.

Example

uses
  ...LCLType, Dialogs, ...;
  ...  
procedure TForm1.Edit1KeyDown(Sender: TObject; var Key: Word;
  Shift: TShiftState);
begin
  // Example: checking for simple keys:
  if (Key = VK_DOWN) or
     (Key = VK_UP) then
    ShowMessage('Pressed arrow up or down key');
  // Check for Alt-F2
  if (Key = VK_F2) and (ssAlt in Shift) then
    ShowMessage('Alt F2 was pressed')
  Key := 0; // Necessary for some widgetsets, e.g. Cocoa, in order to disable processing in subsequent elements.
end;

See also

• Description of keyboard events in Delphi; should be applicable to Lazarus, as well.
• LCL Key Handling Detailed background on key handling in the LCL.
• OnKeyPress

From the Free Pascal wiki, page "key down", as it stood on 2020-02-18 after a change by Trev, out of the wiki's dump of 2024-05-26. Copyright stays with the author who wrote it, according to the old wiki's Licensing page. If you have concerns about this material, message the admin.