event(n) Tk Built-In Commands event(n)______________________________________________________________________________NAME
event - Miscellaneous event facilities: define virtual events and gen‐
erate events
SYNOPSIS
event option ?arg arg ...?
_________________________________________________________________DESCRIPTION
The event command provides several facilities for dealing with window
system events, such as defining virtual events and synthesizing events.
The command has several different forms, determined by the first argu‐
ment. The following forms are currently supported:
event add <<virtual>> sequence ?sequence ...?
Associates the virtual event virtual with the physical event
sequence(s) given by the sequence arguments, so that the virtual
event will trigger whenever any one of the sequences occurs.
Virtual may be any string value and sequence may have any of the
values allowed for the sequence argument to the bind command.
If virtual is already defined, the new physical event sequences
add to the existing sequences for the event.
event delete <<virtual>> ?sequence sequence ...?
Deletes each of the sequences from those associated with the
virtual event given by virtual. Virtual may be any string value
and sequence may have any of the values allowed for the sequence
argument to the bind command. Any sequences not currently asso‐
ciated with virtual are ignored. If no sequence argument is
provided, all physical event sequences are removed for virtual,
so that the virtual event will not trigger anymore.
event generate window event ?option value option value ...?
Generates a window event and arranges for it to be processed
just as if it had come from the window system. Window gives the
path name of the window for which the event will be generated;
it may also be an identifier (such as returned by winfo id) as
long as it is for a window in the current application. Event
provides a basic description of the event, such as <Shift-But‐
ton-2> or <<Paste>>. If Window is empty the whole screen is
meant, and coordinates are relative to the screen. Event may
have any of the forms allowed for the sequence argument of the
bind command except that it must consist of a single event pat‐
tern, not a sequence. Option-value pairs may be used to specify
additional attributes of the event, such as the x and y mouse
position; see EVENT FIELDS below. If the -when option is not
specified, the event is processed immediately: all of the han‐
dlers for the event will complete before the event generate com‐
mand returns. If the -when option is specified then it deter‐
mines when the event is processed. Certain events, such as key
events, require that the window has focus to receive the event
properly.
event info ?<<virtual>>?
Returns information about virtual events. If the <<virtual>>
argument is omitted, the return value is a list of all the vir‐
tual events that are currently defined. If <<virtual>> is spec‐
ified then the return value is a list whose elements are the
physical event sequences currently defined for the given virtual
event; if the virtual event is not defined then an empty string
is returned.
Note that virtual events that that are not bound to physical
event sequences are not returned by event info.
EVENT FIELDS
The following options are supported for the event generate command.
These correspond to the “%” expansions allowed in binding scripts for
the bind command.
-above window
Window specifies the above field for the event, either as a win‐
dow path name or as an integer window id. Valid for Configure
events. Corresponds to the %a substitution for binding scripts.
-borderwidth size
Size must be a screen distance; it specifies the border_width
field for the event. Valid for Configure events. Corresponds
to the %B substitution for binding scripts.
-button number
Number must be an integer; it specifies the detail field for a
ButtonPress or ButtonRelease event, overriding any button num‐
ber provided in the base event argument. Corresponds to the %b
substitution for binding scripts.
-count number
Number must be an integer; it specifies the count field for the
event. Valid for Expose events. Corresponds to the %c substi‐
tution for binding scripts. │
-data string │
String may be any value; it specifies the user_data field for │
the event. Only valid for virtual events. Corresponds to the │
%d substitution for virtual events in binding scripts.
-delta number
Number must be an integer; it specifies the delta field for the
MouseWheel event. The delta refers to the direction and magni‐
tude the mouse wheel was rotated. Note the value is not a
screen distance but are units of motion in the mouse wheel.
Typically these values are multiples of 120. For example, 120
should scroll the text widget up 4 lines and -240 would scroll
the text widget down 8 lines. Of course, other widgets may
define different behaviors for mouse wheel motion. This field
corresponds to the %D substitution for binding scripts.
-detail detail
Detail specifies the detail field for the event and must be one
of the following:
NotifyAncestor NotifyNonlinearVirtual NotifyDetail‐
None NotifyPointer NotifyInferior NotifyPointer‐
Root NotifyNonlinear NotifyVirtual Valid for Enter,
Leave, FocusIn and FocusOut events. Corresponds to the %d sub‐
stitution for binding scripts.
-focus boolean
Boolean must be a boolean value; it specifies the focus field
for the event. Valid for Enter and Leave events. Corresponds
to the %f substitution for binding scripts.
-height size
Size must be a screen distance; it specifies the height field
for the event. Valid for Configure events. Corresponds to the
%h substitution for binding scripts.
-keycode number
Number must be an integer; it specifies the keycode field for
the event. Valid for KeyPress and KeyRelease events. Corre‐
sponds to the %k substitution for binding scripts.
-keysym name
Name must be the name of a valid keysym, such as g, space, or
Return; its corresponding keycode value is used as the keycode
field for event, overriding any detail specified in the base
event argument. Valid for KeyPress and KeyRelease events. Cor‐
responds to the %K substitution for binding scripts.
-mode notify
Notify specifies the mode field for the event and must be one of
NotifyNormal, NotifyGrab, NotifyUngrab, or NotifyWhileGrabbed.
Valid for Enter, Leave, FocusIn, and FocusOut events. Corre‐
sponds to the %m substitution for binding scripts.
-override boolean
Boolean must be a boolean value; it specifies the override_re‐
direct field for the event. Valid for Map, Reparent, and Con‐
figure events. Corresponds to the %o substitution for binding
scripts.
-place where
Where specifies the place field for the event; it must be
either PlaceOnTop or PlaceOnBottom. Valid for Circulate events.
Corresponds to the %p substitution for binding scripts.
-root window
Window must be either a window path name or an integer window
identifier; it specifies the root field for the event. Valid
for KeyPress, KeyRelease, ButtonPress, ButtonRelease, Enter,
Leave, and Motion events. Corresponds to the %R substitution
for binding scripts.
-rootx coord
Coord must be a screen distance; it specifies the x_root field
for the event. Valid for KeyPress, KeyRelease, ButtonPress,
ButtonRelease, Enter, Leave, and Motion events. Corresponds to
the %X substitution for binding scripts.
-rooty coord
Coord must be a screen distance; it specifies the y_root field
for the event. Valid for KeyPress, KeyRelease, ButtonPress,
ButtonRelease, Enter, Leave, and Motion events. Corresponds to
the %Y substitution for binding scripts.
-sendevent boolean
Boolean must be a boolean value; it specifies the send_event
field for the event. Valid for all events. Corresponds to the
%E substitution for binding scripts.
-serial number
Number must be an integer; it specifies the serial field for
the event. Valid for all events. Corresponds to the %# substi‐
tution for binding scripts.
-state state
State specifies the state field for the event. For KeyPress,
KeyRelease, ButtonPress, ButtonRelease, Enter, Leave, and Motion
events it must be an integer value. For Visibility events it
must be one of VisibilityUnobscured, VisibilityPartiallyOb‐
scured, or VisibilityFullyObscured. This option overrides any
modifiers such as Meta or Control specified in the base event.
Corresponds to the %s substitution for binding scripts.
-subwindow window
Window specifies the subwindow field for the event, either as a
path name for a Tk widget or as an integer window identifier.
Valid for KeyPress, KeyRelease, ButtonPress, ButtonRelease,
Enter, Leave, and Motion events. Similar to %S substitution for
binding scripts.
-time integer
Integer must be an integer value; it specifies the time field
for the event. Valid for KeyPress, KeyRelease, ButtonPress,
ButtonRelease, Enter, Leave, Motion, and Property events. Cor‐
responds to the %t substitution for binding scripts.
-warp boolean
boolean must be a boolean value; it specifies whether the
screen pointer should be warped as well. Valid for KeyPress,
KeyRelease, ButtonPress, ButtonRelease, and Motion events. The
pointer will only warp to a window if it is mapped.
-width size
Size must be a screen distance; it specifies the width field
for the event. Valid for Configure events. Corresponds to the
%w substitution for binding scripts.
-when when
When determines when the event will be processed; it must have
one of the following values:
now Process the event immediately, before the command
returns. This also happens if the -when option is
omitted.
tail Place the event on Tcl's event queue behind any events
already queued for this application.
head Place the event at the front of Tcl's event queue, so
that it will be handled before any other events
already queued.
mark Place the event at the front of Tcl's event queue but
behind any other events already queued with -when
mark. This option is useful when generating a series
of events that should be processed in order but at the
front of the queue.
-x coord
Coord must be a screen distance; it specifies the x field for
the event. Valid for KeyPress, KeyRelease, ButtonPress, Button‐
Release, Motion, Enter, Leave, Expose, Configure, Gravity, and
Reparent events. Corresponds to the %x substitution for binding
scripts. If Window is empty the coordinate is relative to the
screen, and this option corresponds to the %X substitution for
binding scripts.
-y coord
Coord must be a screen distance; it specifies the y field for
the event. Valid for KeyPress, KeyRelease, ButtonPress, Button‐
Release, Motion, Enter, Leave, Expose, Configure, Gravity, and
Reparent events. Corresponds to the %y substitution for binding
scripts. If Window is empty the coordinate is relative to the
screen, and this option corresponds to the %Y substitution for
binding scripts.
Any options that are not specified when generating an event are filled
with the value 0, except for serial, which is filled with the next X
event serial number.
PREDEFINED VIRTUAL EVENTS
Tk defines the following virtual events for the purposes of notifica‐
tion:
<<AltUnderlined>>
This is sent to widget to notify it that the letter it has
underlined (as an accelerator indicator) with the -underline
option has been pressed in combination with the Alt key. The
usual response to this is to either focus into the widget (or
some related widget) or to invoke the widget.
<<Invoke>>
This can be sent to some widgets (e.g. button, listbox, menu) as
an alternative to <space>.
<<ListboxSelect>>
This is sent to a listbox when the set of selected item(s) in
the listbox is updated.
<<MenuSelect>>
This is sent to a menu when the currently selected item in the
menu changes. It is intended for use with context-sensitive help
systems.
<<Modified>>
This is sent to a text widget when the contents of the widget
are changed.
<<Selection>>
This is sent to a text widget when the selection in the widget
is changed.
<<ThemeChanged>>
This is sent to a text widget when the ttk (Tile) theme changed.
<<TraverseIn>>
This is sent to a widget when the focus enters the widget
because of a user-driven “tab to widget” action.
<<TraverseOut>>
This is sent to a widget when the focus leaves the widget
because of a user-driven “tab to widget” action.
Tk defines the following virtual events for the purposes of unifying
bindings across multiple platforms. Users expect them to behave in the
following way:
<<Clear>>
Delete the currently selected widget contents.
<<Copy>>
Copy the currently selected widget contents to the clipboard.
<<Cut>>
Move the currently selected widget contents to the clipboard.
<<Paste>>
Replace the currently selected widget contents with the contents
of the clipboard.
<<PasteSelection>>
Insert the contents of the selection at the mouse location.
(This event has meaningful %x and %y substitutions).
<<PrevWindow>>
Traverse to the previous window.
<<Redo>>
Redo one undone action.
<<Undo>>
Undo the last action.
VIRTUAL EVENT EXAMPLES
In order for a virtual event binding to trigger, two things must hap‐
pen. First, the virtual event must be defined with the event add com‐
mand. Second, a binding must be created for the virtual event with the
bind command. Consider the following virtual event definitions:
event add <<Paste>> <Control-y>
event add <<Paste>> <Button-2>
event add <<Save>> <Control-X><Control-S>
event add <<Save>> <Shift-F12>
In the bind command, a virtual event can be bound like any other
builtin event type as follows:
bind Entry <<Paste>> {%W insert [selection get]}
The double angle brackets are used to specify that a virtual event is
being bound. If the user types Control-y or presses button 2, or if a
<<Paste>> virtual event is synthesized with event generate, then the
<<Paste>> binding will be invoked.
If a virtual binding has the exact same sequence as a separate physical
binding, then the physical binding will take precedence. Consider the
following example:
event add <<Paste>> <Control-y> <Meta-Control-y>
bind Entry <Control-y> {puts Control-y}
bind Entry <<Paste>> {puts Paste}
When the user types Control-y the <Control-y> binding will be invoked,
because a physical event is considered more specific than a virtual
event, all other things being equal. However, when the user types
Meta-Control-y the <<Paste>> binding will be invoked, because the Meta
modifier in the physical pattern associated with the virtual binding is
more specific than the <Control-y> sequence for the physical event.
Bindings on a virtual event may be created before the virtual event
exists. Indeed, the virtual event never actually needs to be defined,
for instance, on platforms where the specific virtual event would mean‐
ingless or ungeneratable.
When a definition of a virtual event changes at run time, all windows
will respond immediately to the new definition. Starting from the pre‐
ceding example, if the following code is executed:
bind <Entry> <Control-y> {}
event add <<Paste>> <Key-F6>
the behavior will change such in two ways. First, the shadowed
<<Paste>> binding will emerge. Typing Control-y will no longer invoke
the <Control-y> binding, but instead invoke the virtual event
<<Paste>>. Second, pressing the F6 key will now also invoke the
<<Paste>> binding.
SEE ALSObind(n)KEYWORDS
event, binding, define, handle, virtual event
Tk 8.3 event(n)
