NAME¶
event - Miscellaneous event facilities: define virtual events and generate
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 argument. 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 associated 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-Button-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 pattern,
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 handlers for the
event will complete before the event generate command returns. If
the -when option is specified then it determines 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 virtual events that are currently
defined. If <<virtual>> is specified 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 window 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 number 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 substitution 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 magnitude 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
NotifyDetailNone NotifyPointer
NotifyInferior NotifyPointerRoot
NotifyNonlinear NotifyVirtual
Valid for
Enter,
Leave,
FocusIn and
FocusOut events.
Corresponds to the
%d substitution 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. Corresponds 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. Corresponds 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. Corresponds to
the %m substitution for binding scripts.
- -override boolean
- Boolean must be a boolean value; it specifies the
override_redirect field for the event. Valid for Map,
Reparent, and Configure 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 %# substitution 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, VisibilityPartiallyObscured, 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. Corresponds 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, ButtonRelease,
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, ButtonRelease,
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 notification:
- <<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.
- <<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.
- <<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 happen. First,
the virtual event must be defined with the
event add command. 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 meaningless 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 preceding
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 ALSO¶
bind(3tk)
KEYWORDS¶
event, binding, define, handle, virtual event