Difference between revisions of "key down"
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== Overview == | == Overview == | ||
+ | |||
The {{Doc|package=LCL|unit=controls|identifier=twincontrol.onkeydown|text=OnKeyDown}} event of an object allows you to check what key the user has pressed. | The {{Doc|package=LCL|unit=controls|identifier=twincontrol.onkeydown|text=OnKeyDown}} event of an object allows you to check what key the user has pressed. | ||
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{{Note|''OnKeyDown'' doesn't support Unicode characters. If you need Unicode characters but no control characters, use {{Doc|package=LCL|unit=controls|identifier=twincontrol.onutf8keypress|text=OnUTF8KeyPress}}.}} | {{Note|''OnKeyDown'' doesn't support Unicode characters. If you need Unicode characters but no control characters, use {{Doc|package=LCL|unit=controls|identifier=twincontrol.onutf8keypress|text=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 == | == Example == | ||
− | <syntaxhighlight> | + | |
+ | <syntaxhighlight lang=pascal> | ||
uses | uses | ||
...LCLType, Dialogs, ...; | ...LCLType, Dialogs, ...; | ||
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if (Key = VK_F2) and (ssAlt in Shift) then | if (Key = VK_F2) and (ssAlt in Shift) then | ||
ShowMessage('Alt F2 was pressed') | ShowMessage('Alt F2 was pressed') | ||
+ | Key := 0; // Necessary for some widgetsets, e.g. Cocoa, in order to disable processing in subsequent elements. | ||
end; | end; | ||
</syntaxhighlight> | </syntaxhighlight> | ||
== See also == | == See also == | ||
+ | |||
* [http://delphi.about.com/od/objectpascalide/a/keyboard_events.htm Description of keyboard events in Delphi]; should be applicable to Lazarus, as well. | * [http://delphi.about.com/od/objectpascalide/a/keyboard_events.htm Description of keyboard events in Delphi]; should be applicable to Lazarus, as well. | ||
* [[LCL Key Handling]] Detailed background on key handling in the LCL. | * [[LCL Key Handling]] Detailed background on key handling in the LCL. | ||
− | + | * [[OnKeyPress]] | |
− | [[ |
Latest revision as of 08:32, 18 February 2020
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Deutsch (de) │
English (en) │
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