bind(3pm) User Contributed Perl Documentation bind(3pm)
NAME
Tk::bind - Arrange for X events to invoke callbacks
SYNOPSIS
Retrieve bindings:
$widget->bind
$widget->bind(tag)
$widget->bind(sequence)
$widget->bind(tag,sequence)
Associate and destroy bindings:
$widget->bind(sequence,callback)
$widget->bind(tag,sequence,callback)
DESCRIPTION
The bind method associates callbacks with X events. If callback is
specified, bind will arrange for callback to be evaluated whenever the
event(s) given by sequence occur in the window(s) identified by $widget
or tag. If callback is an empty string then the current binding for
sequence is destroyed, leaving sequence unbound. In all of the cases
where a callback argument is provided, bind returns an empty string.
If sequence is specified without a callback, then the callback currently
bound to sequence is returned, or undef is returned if there is no
binding for sequence. If neither sequence nor callback is specified,
then the return value is a list whose elements are all the sequences for
which there exist bindings for tag.
If no tag is specified then the bind refers to $widget. If tag is
specified then it is typically a class name and the bind refers to all
instances of the class on the MainWindow associated with $widget. (It is
possible for tag to be another "widget object" but this practice is
deprecated.) Perl's ref($object) can be used to get the class name of
any object. Each window has an associated list of tags, and a binding
applies to a particular window if its tag is among those specified for
the window. Although the bindtags method may be used to assign an
arbitrary set of binding tags to a window, the default binding tags
provide the following behavior:
If a tag is the name of an internal window the binding applies to that
window.
If the tag is the name of a toplevel window the binding applies to the
toplevel window and all its internal windows.
If the tag is the name of a class of widgets, such as Tk::Button, the
binding applies to all widgets in that class;
If tag has the value all, the binding applies to all windows descended
from the MainWindow of the application.
EVENT PATTERNS
The sequence argument specifies a sequence of one or more event
patterns, with optional white space between the patterns. Each event
pat may take one of three forms. In the simplest case it is a single
printing ASCII character, such as a or [. The character may not be a
space character or the character <. This form of pattern matches a
KeyPress event for the particular character. The second form of pattern
is longer but more general. It has the following syntax:
'<modifier-modifier-type-detail>'
The entire event pattern is surrounded by angle brackets, and normally
needs to be quoted, as angle brackets are special to perl. Inside the
angle brackets are zero or more modifiers, an event type, and an extra
piece of information (detail) identifying a particular button or keysym.
Any of the fields may be omitted, as long as at least one of type and
detail is present. The fields must be separated by white space or
dashes.
The third form of pattern is used to specify a user-defined, named
virtual event; see Tk::event for details. It has the following syntax:
'<<name>>'
The entire virtual event pattern is surrounded by double angle brackets.
Inside the angle brackets is the user-defined name of the virtual event.
Modifiers, such as Shift or Control, may not be combined with a virtual
event to modify it. Bindings on a virtual event may be created before
the virtual event is defined, and if the definition of a virtual event
changes dynamically, all windows bound to that virtual event will
respond immediately to the new definition.
MODIFIERS
Modifiers consist of any of the following values:
Control Mod2, M2
Shift Mod3, M3
Lock Mod4, M4
Button1, B1 Mod5, M5
Button2, B2 Meta, M
Button3, B3 Alt
Button4, B4 Double
Button5, B5 Triple
Mod1, M1 Quadruple
Where more than one value is listed, separated by commas, the values are
equivalent. Most of the modifiers have the obvious X meanings. For
example, Button1 requires that button 1 be depressed when the event
occurs. For a binding to match a given event, the modifiers in the
event must include all of those specified in the event pattern. An
event may also contain additional modifiers not specified in the
binding. For example, if button 1 is pressed while the shift and
control keys are down, the pattern <Control-Button-1> will match the
event, but <Mod1-Button-1> will not. If no modifiers are specified,
then any combination of modifiers may be present in the event.
Meta and M refer to whichever of the M1 through M5 modifiers is
associated with the meta key(s) on the keyboard (keysyms Meta_R and
Meta_L). If there are no meta keys, or if they are not associated with
any modifiers, then Meta and M will not match any events. Similarly,
the Alt modifier refers to whichever modifier is associated with the alt
key(s) on the keyboard (keysyms Alt_L and Alt_R).
The Double, Triple and Quadruple modifiers are a convenience for
specifying double mouse clicks and other repeated events. They cause a
particular event pattern to be repeated 2, 3 or 4 times, and also place
a time and space requirement on the sequence: for a sequence of events
to match a Double, Triple or Quadruple pattern, all of the events must
occur close together in time and without substantial mouse motion in
between. For example, <Double-Button-1> is equivalent to
<Button-1><Button-1> with the extra time and space requirement.
EVENT TYPES
The type field may be any of the standard X event types, with a few
extra abbreviations. Below is a list of all the valid types; where two
names appear together, they are synonyms.
Activate Destroy Map
ButtonPress, Button Enter MapRequest
ButtonRelease Expose Motion
Circulate FocusIn MouseWheel
CirculateRequest FocusOut Property
Colormap Gravity Reparent
Configure KeyPress, Key ResizeRequest
ConfigureRequest KeyRelease Unmap
Create Leave Visibility
Deactivate
Most of the above events have the same fields and behaviors as events
in the X Windowing system. You can find more detailed descriptions of
these events in any X window programming book. A couple of the events
are extensions to the X event system to support features unique to the
Macintosh and Windows platforms. We provide a little more detail on
these events here. These include:
Activate
Deactivate
These two events are sent to every sub-window of a toplevel when they
change state. In addition to the focus Window, the Macintosh platform
and Windows platforms have a notion of an active window (which often has
but is not required to have the focus). On the Macintosh, widgets in
the active window have a different appearance than widgets in deactive
windows. The Activate event is sent to all the sub-windows in a
toplevel when it changes from being deactive to active. Likewise, the
Deactive event is sent when the window's state changes from active to
deactive. There are no use- ful percent substitutions you would make
when binding to these events.
MouseWheel
Some mice on the Windows platform support a mouse wheel which is used
for scrolling documents without using the scrollbars. By rolling the
wheel, the system will generate MouseWheel events that the application
can use to scroll. Like Key events the event is always routed to the
window that currently has focus. When the event is received you can
use the %D substitution to get the delta field for the event which is a
integer value of motion that the mouse wheel has moved. The
smallest value for which the system will report is defined by the OS.
On Windows 95 & 98 machines this value is at least 120 before it is
reported. However, higher resolution devices may be available in the
future. The sign of the value determines which direction your
widget should scroll. Positive values should scroll up and negative
values should scroll down.
The last part of a long event specification is detail. In the case of a
ButtonPress or ButtonRelease event, it is the number of a button (1-5).
If a button number is given, then only an event on that particular
button will match; if no button number is given, then an event on any
button will match. Note: giving a specific button number is different
than specifying a button modifier; in the first case, it refers to a
button being pressed or released, while in the second it refers to some
other button that is already depressed when the matching event occurs.
If a button number is given then type may be omitted: if will default
to ButtonPress. For example, the specifier <1> is equivalent to
<ButtonPress-1>.
If the event type is KeyPress or KeyRelease, then detail may be
specified in the form of an X keysym. Keysyms are textual
specifications for particular keys on the keyboard; they include all the
alphanumeric ASCII characters (e.g. ``a'' is the keysym for the ASCII
character ``a''), plus descriptions for non-alphanumeric characters
(``comma'' is the keysym for the comma character), plus descriptions for
all the non-ASCII keys on the keyboard (``Shift_L'' is the keysm for the
left shift key, and ``F1'' is the keysym for the F1 function key, if it
exists). The complete list of keysyms is not presented here; it is
available in other X documentation and may vary from system to system.
If necessary, you can use the 'K' notation described below to print out
the keysym name for a particular key. If a keysym detail is given, then
the type field may be omitted; it will default to KeyPress. For
example, <Control-comma> is equivalent to <Control-KeyPress-comma>.
BINDING CALLBACKS AND SUBSTITUTIONS
The callback argument to bind is a perl/Tk callback. which will be
executed whenever the given event sequence occurs. (See Tk::callbacks
for description of the possible forms.) Callback will be associated
with the same MainWindow that is associated with the $widget that was
used to invoke the bind method, and it will run as though called from
MainLoop. If callback contains any Ev(%) calls, then each "nested"
Ev(%) "callback" will be evaluated when the event occurs to form
arguments to be passed to the main callback. The replacement depends on
the character %, as defined in the list below. Unless otherwise
indicated, the replacement string is the numeric (decimal) value of the
given field from the current event. Perl/Tk has enhanced this mechanism
slightly compared to the comparable Tcl/Tk mechanism. The enhancements
are not yet all reflected in the list below. Some of the substitutions
are only valid for certain types of events; if they are used for other
types of events the value substituted is undefined (not the same as
undef!).
'#' The number of the last client request processed by the server (the
serial field from the event). Valid for all event types.
'a' The above field from the event, formatted as a hexadecimal number.
Valid only for Configure events.
'b' The number of the button that was pressed or released. Valid only
for ButtonPress and ButtonRelease events.
'c' The count field from the event. Valid only for Expose events.
'd' The detail field from the event. The 'd' is replaced by a string
identifying the detail. For Enter, Leave, FocusIn, and FocusOut
events, the string will be one of the following:
NotifyAncestor NotifyNonlinearVirtual
NotifyDetailNone NotifyPointer
NotifyInferior NotifyPointerRoot
NotifyNonlinear NotifyVirtual
For ConfigureRequest events, the string will be one of:
Above Opposite
Below None
BottomIf TopIf
For events other than these, the substituted string is undefined.
(Note that this is not the same as Detail part of sequence use to
specify the event.)
'f' The focus field from the event (0 or 1). Valid only for Enter and
Leave events.
'h' The height field from the event. Valid only for Configure,
ConfigureRequest, Create, Expose, and ResizeRequest events.
'i' The window field from the event, represented as a hexadecimal
integer.
'k' The keycode field from the event. Valid only for KeyPress and
KeyRelease events.
'm' The mode field from the event. The substituted string is one of
NotifyNormal, NotifyGrab, NotifyUngrab, or NotifyWhileGrabbed.
Valid only for Enter, FocusIn, FocusOut, and Leave events.
'o' The override_redirect field from the event. Valid only for Map,
Reparent, and Configure events.
'p' The place field from the event, substituted as one of the strings
PlaceOnTop or PlaceOnBottom. Valid only for Circulate and
CirculateRequest events.
's' The state field from the event. For ButtonPress, ButtonRelease,
Enter, KeyPress, KeyRelease, Leave, and Motion events, a decimal
string is substituted. For Visibility, one of the strings
VisibilityUnobscured, VisibilityPartiallyObscured, and
VisibilityFullyObscured is substituted.
't' The time field from the event. Valid only for events that contain a
time field.
'w' The width field from the event. Valid only for Configure,
ConfigueRequest, Create, Expose, and ResizeREquest events.
'x' The x field from the event. Valid only for events containing an x
field.
'y' The y field from the event. Valid only for events containing a y
field.
'@' The string "@x,y" where x and y are as above. Valid only for events
containing x and y fields. This format is used my methods of
Tk::Text and similar widgets.
'A' Substitutes the UNICODE character corresponding to the event, or the
empty string if the event doesn't correspond to a UNICODE character
(e.g. the shift key was pressed). XmbLookupString does all the work
of translating from the event to a UNICODE character. Valid only
for KeyPress and KeyRelease events.
'B' The border_width field from the event. Valid only for Configure,
ConfigureRequest and Create events.
'D' This reports the delta value of a MouseWheel event. The delta
value represents the rotation units the mouse wheel has been
moved. On Windows 95 & 98 systems the smallest value for the
delta is 120. Future systems may support higher resolution values
for the delta. The sign of the value represents the direction the
mouse wheel was scrolled.
'E' The send_event field from the event. Valid for all event types.
'K' The keysym corresponding to the event, substituted as a textual
string. Valid only for KeyPress and KeyRelease events.
'N' The keysym corresponding to the event, substituted as a decimal
number. Valid only for KeyPress and KeyRelease events.
'R' The root window identifier from the event. Valid only for events
containing a root field.
'S' The subwindow window identifier from the event, as an object if it
is one otherwise as a hexadecimal number. Valid only for events
containing a subwindow field.
'T' The type field from the event. Valid for all event types.
'W' The window to which the event was reported (the $widget field from
the event) - as an perl/Tk object. Valid for all event types.
'X' The x_root field from the event. If a virtual-root window manager
is being used then the substituted value is the corresponding
x-coordinate in the virtual root. Valid only for ButtonPress,
ButtonRelease, KeyPress, KeyRelease, and Motion events.
'Y' The y_root field from the event. If a virtual-root window manager
is being used then the substituted value is the corresponding
y-coordinate in the virtual root. Valid only for ButtonPress,
ButtonRelease, KeyPress, KeyRelease, and Motion events.
MULTIPLE MATCHES
It is possible for several bindings to match a given X event. If the
bindings are associated with different tag's, then each of the bindings
will be executed, in order. By default, a class binding will be
executed first, followed by a binding for the widget, a binding for its
toplevel, and an all binding. The bindtags method may be used to change
this order for a particular window or to associate additional binding
tags with the window.
return and Tk->break may be used inside a callback to control the
processing of matching callbacks. If return is invoked, then the
current callback is terminated but Tk will continue processing callbacks
associated with other tag's. If Tk->break is invoked within a callback,
then that callback terminates and no other callbacks will be invoked for
the event. (Tk->break is implemented via perl's die with a special
value which is "caught" by the perl/Tk "glue" code.)
If more than one binding matches a particular event and they have the
same tag, then the most specific binding is chosen and its callback is
evaluated. The following tests are applied, in order, to determine
which of several matching sequences is more specific: (a) an event
pattern that specifies a specific button or key is more specific than
one that doesn't; (b) a longer sequence (in terms of number of events
matched) is more specific than a shorter sequence; (c) if the modifiers
specified in one pattern are a subset of the modifiers in another
pattern, then the pattern with more modifiers is more specific. (d) a
virtual event whose physical pattern matches the sequence is less
specific than the same physical pattern that is not associated with a
virtual event. (e) given a sequence that matches two or more virtual
events, one of the virtual events will be chosen, but the order is
undefined.
If the matching sequences contain more than one event, then tests
(c)-(e) are applied in order from the most recent event to the least
recent event in the sequences. If these tests fail to determine a
winner, then the most recently registered sequence is the winner.
If there are two (or more) virtual events that are both triggered by the
same sequence, and both of those virtual events are bound to the same
window tag, then only one of the virtual events will be triggered, and
it will be picked at random:
$widget->eventAdd('<<Paste>>' => '<Control-y>');
$widget->eventAdd('<<Paste>>' => '<Button-2>');
$widget->eventAdd <<Scroll>>' => '<Button-2>');
$widget->bind('Tk::Entry','<<Paste>>',sub { print 'Paste'});
$widget->bind('Tk::Entry','<<Scroll>>', sub {print 'Scroll'});
If the user types Control-y, the <<Paste>> binding will be invoked, but
if the user presses button 2 then one of either the <<Paste>> or the
<<Scroll>> bindings will be invoked, but exactly which one gets invoked
is undefined.
If an X event does not match any of the existing bindings, then the
event is ignored. An unbound event is not considered to be an error.
MULTI-EVENT SEQUENCES AND IGNORED EVENTS
When a sequence specified in a bind method contains more than one event
pattern, then its callback is executed whenever the recent events
(leading up to and including the current event) match the given
sequence. This means, for example, that if button 1 is clicked
repeatedly the sequence <Double-ButtonPress-1> will match each button
press but the first. If extraneous events that would prevent a match
occur in the middle of an event sequence then the extraneous events are
ignored unless they are KeyPress or ButtonPress events. For example,
<Double-ButtonPress-1> will match a sequence of presses of button 1,
even though there will be ButtonRelease events (and possibly Motion
events) between the ButtonPress events. Furthermore, a KeyPress event
may be preceded by any number of other KeyPress events for modifier keys
without the modifier keys preventing a match. For example, the event
sequence aB will match a press of the a key, a release of the a key, a
press of the Shift key, and a press of the b key: the press of Shift is
ignored because it is a modifier key. Finally, if several Motion events
occur in a row, only the last one is used for purposes of matching
binding sequences.
ERRORS
If an error occurs in executing the callback for a binding then the
Tk::Error mechanism is used to report the error. The Tk::Error
mechanism will be executed at same call level, and associated with the
same MainWindow as as the callback was invoked.
CAVEATS
Note that for the Canvas widget, the call to bind has to be fully
qualified. This is because there is already a bind method for the Canvas
widget, which binds individual canvas tags.
$canvas->Tk::bind
SEE ALSO
Tk::Error Tk::callbacks Tk::bindtags
KEYWORDS
Event, binding
perl v5.40.1 2025-04-13 bind(3pm)
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