View Source wxKeyEvent (wx v2.4.3)
This event class contains information about key press and release events.
The main information carried by this event is the key being pressed or released. It can
be accessed using either getKeyCode/1
function or getUnicodeKey/1
. For the printable characters, the latter should be
used as it works for any keys, including non-Latin-1 characters that can be entered when
using national keyboard layouts. getKeyCode/1
should be used to handle special characters (such as
cursor arrows keys or HOME
or INS
and so on) which correspond to ?wxKeyCode enum
elements above the WXK_START
constant. While getKeyCode/1
also returns the character code for
Latin-1 keys for compatibility, it doesn't work for Unicode characters in general and will
return WXK_NONE
for any non-Latin-1 ones. For this reason, it's recommended to always
use getUnicodeKey/1
and only fall back to getKeyCode/1
if getUnicodeKey/1
returned WXK_NONE
meaning that the event corresponds to
a non-printable special keys.
While both of these functions can be used with the events of wxEVT_KEY_DOWN
, wxEVT_KEY_UP
and wxEVT_CHAR
types, the values returned by them are different for the first two
events and the last one. For the latter, the key returned corresponds to the character
that would appear in e.g. a text zone if the user pressed the key in it. As such, its
value depends on the current state of the Shift key and, for the letters, on the state of
Caps Lock modifier. For example, if A
key is pressed without Shift being held down, wxKeyEvent
of type wxEVT_CHAR
generated for this key press will return (from either getKeyCode/1
or getUnicodeKey/1
as their
meanings coincide for ASCII characters) key code of 97 corresponding the ASCII value of a
.
And if the same key is pressed but with Shift being held (or Caps Lock being active), then
the key could would be 65, i.e. ASCII value of capital A
.
However for the key down and up events the returned key code will instead be A
independently of the state of the modifier keys i.e. it depends only on physical key being
pressed and is not translated to its logical representation using the current keyboard
state. Such untranslated key codes are defined as follows:
For the letters they correspond to the
upper
case value of the letter.For the other alphanumeric keys (e.g.
7
or+
), the untranslated key code corresponds to the character produced by the key when it is pressed without Shift. E.g. in standard US keyboard layout the untranslated key code for the key=/+
in the upper right corner of the keyboard is 61 which is the ASCII value of=
.For the rest of the keys (i.e. special non-printable keys) it is the same as the normal key code as no translation is used anyhow.
Notice that the first rule applies to all Unicode letters, not just the usual Latin-1
ones. However for non-Latin-1 letters only getUnicodeKey/1
can be used to retrieve the key code as getKeyCode/1
just
returns WXK_NONE
in this case.
To summarize: you should handle wxEVT_CHAR
if you need the translated key and wxEVT_KEY_DOWN
if you only need the value of the key itself, independent of the current keyboard state.
Note: Not all key down events may be generated by the user. As an example, wxEVT_KEY_DOWN
with =
key code can be generated using the standard US keyboard layout but not using
the German one because the =
key corresponds to Shift-0 key combination in this layout
and the key code for it is 0
, not =
. Because of this you should avoid requiring your
users to type key events that might be impossible to enter on their keyboard.
Another difference between key and char events is that another kind of translation is
done for the latter ones when the Control key is pressed: char events for ASCII letters in
this case carry codes corresponding to the ASCII value of Ctrl-Latter, i.e. 1 for Ctrl-A,
2 for Ctrl-B and so on until 26 for Ctrl-Z. This is convenient for terminal-like
applications and can be completely ignored by all the other ones (if you need to handle
Ctrl-A it is probably a better idea to use the key event rather than the char one). Notice
that currently no translation is done for the presses of [, \
, ], ^
and _
keys which
might be mapped to ASCII values from 27 to 31. Since version 2.9.2, the enum values WXK_CONTROL_A
WXK_CONTROL_Z
can be used instead of the non-descriptive constant values 1-26.
Finally, modifier keys only generate key events but no char events at all. The modifiers
keys are WXK_SHIFT
, WXK_CONTROL
, WXK_ALT
and various WXK_WINDOWS_XXX
from
?wxKeyCode enum.
Modifier keys events are special in one additional aspect: usually the keyboard state
associated with a key press is well defined, e.g. shiftDown/1
returns true
only if the Shift key
was held pressed when the key that generated this event itself was pressed. There is an
ambiguity for the key press events for Shift key itself however. By convention, it is
considered to be already pressed when it is pressed and already released when it is
released. In other words, wxEVT_KEY_DOWN
event for the Shift key itself will have wxMOD_SHIFT
in getModifiers/1
and shiftDown/1
will return true while the wxEVT_KEY_UP
event for Shift itself will not have wxMOD_SHIFT
in its modifiers and shiftDown/1
will return false.
Tip:
You may discover the key codes and modifiers generated by all the keys on your
system interactively by running the page_samples_keyboard wxWidgets sample and pressing
some keys in it.
Note: If a key down (EVT_KEY_DOWN
) event is caught and the event handler does not call event.Skip()
then the corresponding char event (EVT_CHAR
) will not happen. This is by design and
enables the programs that handle both types of events to avoid processing the same key
twice. As a consequence, if you do not want to suppress the wxEVT_CHAR
events for the
keys you handle, always call event.Skip()
in your wxEVT_KEY_DOWN
handler. Not doing
may also prevent accelerators defined using this key from working.
Note: If a key is maintained in a pressed state, you will typically get a lot of (automatically generated) key down events but only one key up one at the end when the key is released so it is wrong to assume that there is one up event corresponding to each down one.
Note: For Windows programmers: The key and char events in wxWidgets are similar to but
slightly different from Windows WM_KEYDOWN
and WM_CHAR
events. In particular, Alt-x
combination will generate a char event in wxWidgets (unless it is used as an accelerator)
and almost all keys, including ones without ASCII equivalents, generate char events too.
This class is derived, and can use functions, from:
wxWidgets docs: wxKeyEvent
Events
Use wxEvtHandler:connect/3
with wxKeyEventType
to subscribe to events of this type.
Summary
Functions
Returns true if the Alt key is pressed.
Returns true if the key used for command accelerators is pressed.
Returns true if the Control key or Apple/Command key under macOS is pressed.
Returns the key code of the key that generated this event.
Return the bit mask of all pressed modifier keys.
Obtains the position (in client coordinates) at which the key was pressed.
Returns the raw key code for this event.
Returns the low level key flags for this event.
Returns the Unicode character corresponding to this key event.
Returns the X position (in client coordinates) of the event.
Returns the Y position (in client coordinates) of the event.
Returns true if Control or Alt are pressed.
Returns true if the Meta/Windows/Apple key is pressed.
Returns true if the Shift key is pressed.
Types
-type wxKeyEvent() :: wx:wx_object().
-type wxKeyEventType() :: char | char_hook | key_down | key_up.
Functions
-spec altDown(This) -> boolean() when This :: wxKeyEvent().
Returns true if the Alt key is pressed.
Notice that getModifiers/1
should usually be used instead of this one.
-spec cmdDown(This) -> boolean() when This :: wxKeyEvent().
Returns true if the key used for command accelerators is pressed.
Same as controlDown/1
. Deprecated.
Notice that getModifiers/1
should usually be used instead of this one.
-spec controlDown(This) -> boolean() when This :: wxKeyEvent().
Returns true if the Control key or Apple/Command key under macOS is pressed.
This function doesn't distinguish between right and left control keys.
Notice that getModifiers/1
should usually be used instead of this one.
-spec getKeyCode(This) -> integer() when This :: wxKeyEvent().
Returns the key code of the key that generated this event.
ASCII symbols return normal ASCII values, while events from special keys such as "left
cursor arrow" (WXK_LEFT
) return values outside of the ASCII range. See ?wxKeyCode for a
full list of the virtual key codes.
Note that this method returns a meaningful value only for special non-alphanumeric keys
or if the user entered a Latin-1 character (this includes ASCII and the accented letters
found in Western European languages but not letters of other alphabets such as e.g.
Cyrillic). Otherwise it simply method returns WXK_NONE
and getUnicodeKey/1
should be used to obtain the
corresponding Unicode character.
Using getUnicodeKey/1
is in general the right thing to do if you are interested in the characters typed
by the user, getKeyCode/1
should be only used for special keys (for which getUnicodeKey/1
returns WXK_NONE
). To
handle both kinds of keys you might write:
-spec getModifiers(This) -> integer() when This :: wxKeyEvent().
Return the bit mask of all pressed modifier keys.
The return value is a combination of wxMOD_ALT
, wxMOD_CONTROL
, wxMOD_SHIFT
and wxMOD_META
bit masks. Additionally, wxMOD_NONE
is defined as 0, i.e. corresponds to no modifiers
(see HasAnyModifiers()
(not implemented in wx)) and wxMOD_CMD
is either wxMOD_CONTROL
(MSW and Unix) or wxMOD_META
(Mac), see cmdDown/1
. See ?wxKeyModifier for the full list of modifiers.
Notice that this function is easier to use correctly than, for example, controlDown/1
because when
using the latter you also have to remember to test that none of the other modifiers is pressed:
and forgetting to do it can result in serious program bugs (e.g. program not working with
European keyboard layout where AltGr
key which is seen by the program as combination of
CTRL and ALT is used). On the other hand, you can simply write:
with this function.
-spec getPosition(This) -> {X :: integer(), Y :: integer()} when This :: wxKeyEvent().
Obtains the position (in client coordinates) at which the key was pressed.
Notice that under most platforms this position is simply the current mouse pointer position and has no special relationship to the key event itself.
x
and y
may be NULL if the corresponding coordinate is not needed.
-spec getRawKeyCode(This) -> integer() when This :: wxKeyEvent().
Returns the raw key code for this event.
The flags are platform-dependent and should only be used if the functionality provided by
other wxKeyEvent
methods is insufficient.
Under MSW, the raw key code is the value of wParam
parameter of the corresponding message.
Under GTK, the raw key code is the keyval
field of the corresponding GDK event.
Under macOS, the raw key code is the keyCode
field of the corresponding NSEvent.
Note: Currently the raw key codes are not supported by all ports, use #ifdef wxHAS_RAW_KEY_CODES to determine if this feature is available.
-spec getRawKeyFlags(This) -> integer() when This :: wxKeyEvent().
Returns the low level key flags for this event.
The flags are platform-dependent and should only be used if the functionality provided by
other wxKeyEvent
methods is insufficient.
Under MSW, the raw flags are just the value of lParam
parameter of the corresponding message.
Under GTK, the raw flags contain the hardware_keycode
field of the corresponding GDK event.
Under macOS, the raw flags contain the modifiers state.
Note: Currently the raw key flags are not supported by all ports, use #ifdef wxHAS_RAW_KEY_CODES to determine if this feature is available.
-spec getUnicodeKey(This) -> integer() when This :: wxKeyEvent().
Returns the Unicode character corresponding to this key event.
If the key pressed doesn't have any character value (e.g. a cursor key) this method will
return WXK_NONE
. In this case you should use getKeyCode/1
to retrieve the value of the key.
This function is only available in Unicode build, i.e. when wxUSE_UNICODE
is 1.
-spec getX(This) -> integer() when This :: wxKeyEvent().
Returns the X position (in client coordinates) of the event.
See: getPosition/1
-spec getY(This) -> integer() when This :: wxKeyEvent().
Returns the Y position (in client coordinates) of the event.
See: getPosition/1
-spec hasModifiers(This) -> boolean() when This :: wxKeyEvent().
Returns true if Control or Alt are pressed.
Checks if Control, Alt or, under macOS only, Command key are pressed (notice that the real Control key is still taken into account under OS X too).
This method returns false if only Shift is pressed for compatibility reasons and also
because pressing Shift usually doesn't change the interpretation of key events, see HasAnyModifiers()
(not implemented in wx) if you want to take Shift into account as well.
-spec metaDown(This) -> boolean() when This :: wxKeyEvent().
Returns true if the Meta/Windows/Apple key is pressed.
This function tests the state of the key traditionally called Meta under Unix systems,
Windows keys under MSW Notice that getModifiers/1
should usually be used instead of this one.
See: cmdDown/1
-spec shiftDown(This) -> boolean() when This :: wxKeyEvent().
Returns true if the Shift key is pressed.
This function doesn't distinguish between right and left shift keys.
Notice that getModifiers/1
should usually be used instead of this one.