key down: what changed
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Title: key down
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| 1 | + | ## Overview | |
| 2 | + | ||
| 3 | + | The [OnKeyDown](https://lazarus-ccr.sourceforge.io/docs/lcl/controls/twincontrol.onkeydown.html) event of an object allows you to check what key the user has pressed. | |
| 4 | + | ||
| 5 | + | 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. | |
| 6 | + | ||
| 7 | + | > **Note:** *OnKeyDown* doesn't support Unicode characters. If you need Unicode characters but no control characters, use [OnUTF8KeyPress](https://lazarus-ccr.sourceforge.io/docs/lcl/controls/twincontrol.onutf8keypress.html). | |
| 8 | + | ||
| 9 | + | > **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. | |
| 10 | + | ||
| 11 | + | ## Example | |
| 12 | + | ||
| 13 | + | ``` pascal | |
| 14 | + | uses | |
| 15 | + | ...LCLType, Dialogs, ...; | |
| 16 | + | ... | |
| 17 | + | procedure TForm1.Edit1KeyDown(Sender: TObject; var Key: Word; | |
| 18 | + | Shift: TShiftState); | |
| 19 | + | begin | |
| 20 | + | // Example: checking for simple keys: | |
| 21 | + | if (Key = VK_DOWN) or | |
| 22 | + | (Key = VK_UP) then | |
| 23 | + | ShowMessage('Pressed arrow up or down key'); | |
| 24 | + | // Check for Alt-F2 | |
| 25 | + | if (Key = VK_F2) and (ssAlt in Shift) then | |
| 26 | + | ShowMessage('Alt F2 was pressed') | |
| 27 | + | Key := 0; // Necessary for some widgetsets, e.g. Cocoa, in order to disable processing in subsequent elements. | |
| 28 | + | end; | |
| 29 | + | ``` | |
| 30 | + | ||
| 31 | + | ## See also | |
| 32 | + | ||
| 33 | + | - [Description of keyboard events in Delphi](http://delphi.about.com/od/objectpascalide/a/keyboard_events.htm); should be applicable to Lazarus, as well. | |
| 34 | + | - [[LCL Key Handling]] Detailed background on key handling in the LCL. | |
| 35 | + | - [[OnKeyPress]] | |
| 36 | + | ||
| 37 | + | --- | |
| 38 | + | *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](/wiki-contact).* |