Question

How capture keypress on a window using WN_ messages

Asked by: Antenor

I need capture keys pressed in my form (contains very panels and flat buttons only) and filter only keys: PGDN, PGUP, DOWN and UP for scroll controling.

It is possible througth procedures od type messages WN_ ?

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Asked On
2009-09-24 at 12:47:13ID24759827
Tags

Delphi

,

Events

Topic

Delphi IDE

Participating Experts
3
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500
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Answers

 

by: 8080_DiverPosted on 2009-09-24 at 13:03:02ID: 25417241

It would probably be easier to put an On Key Press event handler on your form.  THat would let you capture any keys being pressed while your form (or any of its components) has focus.  You could then set up a CASE statement that would change any keys other than <PageUp>, <PageDown>, <Up>, or <Down> to #07 (the "bell" character).

By the way, when you say "(contains very panels and flat buttons only)" . . . what kind of panels are those?

 

by: AntenorPosted on 2009-09-24 at 13:29:02ID: 25417525

I do one test with a new form and its works.

The problem is when have buttons or edit components. I have assign a 'keydown' event to each component.

Does not exists one way more simple?

 

by: epasquierPosted on 2009-09-24 at 14:50:10ID: 25418365

Use the KeyPreview property of your form, set it to True

This will trigger all Key related events of your form, wherever the focus might be in your controls

onKeyPressed will trigger when an ASCII key is detected. Meaning 'A', '9', '+', '$', Ctrl keys like Enter or Backspace (see an ascii table for reference of these) but will not react to F1, UP, DOWN and combinations

onKeyDown (or Up) is what you need when you want to react to special keys, and the status of Shift, Control.

 

by: 8080_DiverPosted on 2009-09-24 at 14:57:18ID: 25418417

Atenor,

epasquier more fully explained what I was saying.  However, if you have hot-keys assigned to various buttons, you may need to set up a somewhat generic OnKeyPress event that you can then assign to each of the components other than those buttons.  (You can use the same OnKeyPress for multiple components. ;-)  

In either case, you are going to have a trade-off regarding how you handle the key presses.  If you have the form handle all of them but you want to use the hot-keys (e.g. the "x" of "E&xit" for the Exit function) then you are going ot have to code a more complex event handler.  If you code the generic event handler in my second suggestion, then you have a simpler event handler but you have to set the OnKeyPress events of more components to use that event handler.

 

by: KoenVandemoortelPosted on 2009-09-25 at 01:59:10ID: 25421159

I use this to scroll throught a table using the arrow keys in an TEdit that is also used to search (locate('Field1', Edit1.Text, [loPartialKey]). Very convenient.
The form's KeyPreview should be set to False in this case!

procedure TForm1.Edit1KeyDown(Sender: TObject; var Key: Word; Shift: TShiftState);
begin
with Table1 do
  case Key of
    VK_UP:
      begin
      key:=0;
      prior;
      end;
    VK_DOWN:
      begin
      key:=0;
      Next;
      end;
    VK_PRIOR: // = PgUp
      begin
      key:=0;
      MoveBy(-10);
      end;
    VK_NEXT:  // = PgDn
      begin
      key:=0;
      MoveBy(10);
      end;
    end;
end;
                                              
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by: epasquierPosted on 2009-09-25 at 04:23:34ID: 25421885

Yes, if you want something to happen only when you are within a field, the code should be in the component event handler.

If it is a general key capture, it has to be in the form + Keypreview.

Keypreview does not have to be set to false for the components to receive those events when they must.
Both will receive it (the form and the component with focus)
The form will have it before, and can set Key := 0 in order to deactivate the component reaction to a key if necessary.

I beleive everything has been said on the subject now.

 

by: AntenorPosted on 2009-09-28 at 14:20:29ID: 25443498

epasquier,

I do test your suggestion... wait a moment please.

20120131-EE-VQP-002

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