View Source wxKeyEvent (wx v2.4.2)
Functions for wxKeyEvent class
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:
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.
See: wxKeyboardState
(not implemented in wx)
This class is derived (and can use functions) from: wxEvent
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.