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Programming => LCL => Topic started by: leduyquang753 on May 04, 2019, 04:02:05 pm

Title: Cannot cancel Enter key press on TEdit
Post by: leduyquang753 on May 04, 2019, 04:02:05 pm
I am making an expression parser with an input box (TEdit) that when a mistake is present in the expression, the caret moves to where it is. So I hook OnKeyPress to the TEdit:

Code: Pascal  [Select][+][-]
  1. procedure TMainWindow.ExpressionKeyPress(Sender: TObject; var Key: char);
  2. begin
  3.   if key = #13 then begin
  4.     self.calculateIt; // This moves the caret when an error happens.
  5.     key := #0; // Supposed to cancel the key press.
  6.   end;
  7. end;

When an erroneous expression is entered, the caret is seen to be moved to the mistake's location, however shortly after, the whole text in the box is selected, which indicates the Enter key was not canceled, despite having the code to do so.

I tried these workarounds:
None of them worked.

Am I doing something wrong or is there a bug in LCL/Windows OS?
Title: Re: Cannot cancel Enter key press on TEdit
Post by: Thaddy on May 04, 2019, 04:34:58 pm
Quote from: leduyquang753 on May 04, 2019, 04:02:05 pm
I tried these workarounds:
  • Hooking an additional OnKeyDown event to cancel the key.
  • Setting TForm.KeyPreview to true.
None of them worked.

Am I doing something wrong or is there a bug in LCL/Windows OS?

Try using OnKeyUp, because only then you can evaluate correctly. (This is a very common error)
Title: Re: Cannot cancel Enter key press on TEdit
Post by: Bart on May 04, 2019, 06:19:42 pm
Use OnEditingDone for that (it is fired when user presses Enter or when user leaves the control).

Bart
Title: Re: Cannot cancel Enter key press on TEdit
Post by: Thaddy on May 04, 2019, 07:32:34 pm
Quote from: Bart on May 04, 2019, 06:19:42 pm
Use OnEditingDone for that (it is fired when user presses Enter or when user leaves the control).

Bart
No.
Title: Re: Cannot cancel Enter key press on TEdit
Post by: jamie on May 04, 2019, 11:11:19 pm
I assume you set "Autofocus" := False ?
Title: Re: Cannot cancel Enter key press on TEdit
Post by: leduyquang753 on May 05, 2019, 02:47:59 am
Quote from: Thaddy on May 04, 2019, 04:34:58 pm
Try using OnKeyUp, because only then you can evaluate correctly. (This is a very common error)

Oh, the key release event is also triggered. You made my day, thank you.
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