tk4.2 User Commands - bind
NAME
bind - Arrange for X events to invoke Tcl scripts
SYNOPSIS
bind tag
bind tag sequence
bind tag sequence script
bind tag sequence +script
INTRODUCTION
The bind command associates Tcl scripts with X events. If
all three arguments are specified, bind will arrange for
script (a Tcl script) to be evaluated whenever the event(s)
given by sequence occur in the window(s) identified by tag.
If script is prefixed with a ``+'', then it is appended to
any existing binding for sequence; otherwise script
replaces any existing binding. If script is an empty string
then the current binding for sequence is destroyed, leaving
sequence unbound. In all of the cases where a script argu-
ment is provided, bind returns an empty string.
If sequence is specified without a script, then the script
currently bound to sequence is returned, or an empty string
is returned if there is no binding for sequence. If neither
sequence nor script is specified, then the return value is a
list whose elements are all the sequences for which there
exist bindings for tag.
The tag argument determines which window(s) the binding
applies to. If tag begins with a dot, as in .a.b.c, then it
must be the path name for a window; otherwise it may be an
arbitrary string. 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 command 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
Button, the binding applies to all widgets in that
class;
If tag has the value all, the binding applies to all
windows in the application.
EVENT PATTERNS
The sequence argument specifies a sequence of one or more
event patterns, with optional white space between the pat-
terns. Each event pattern 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 pat-
tern is longer but more general. It has the following syn-
tax:
<modifier-modifier-type-detail>
The entire event pattern is surrounded by angle brackets.
Inside the angle brackets are zero or more modifiers, an
event type, and an extra piece of information (detail) iden-
tifying 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. 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
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 but-
ton 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 bind-
ing. 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 and Triple modifiers are a convenience for speci-
fying double mouse clicks and other repeated events. They
cause a particular event pattern to be repeated 2 or 3
times, and also place a time and space requirement on the
sequence: for a sequence of events to match a Double or
Triple 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.
ButtonPress, Button Expose Map
ButtonRelease FocusIn Motion
Circulate FocusOut Property
Colormap Gravity Reparent
Configure KeyPress, Key Unmap
Destroy KeyRelease Visibility
Enter Leave Activate
Deactivate
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 tex-
tual 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 neces-
sary, 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 SCRIPTS AND SUBSTITUTIONS
The script argument to bind is a Tcl script, which will be
executed whenever the given event sequence occurs. Command
will be executed in the same interpreter that the bind com-
mand was executed in, and it will run at global level (only
global variables will be accessible). If script contains
any % characters, then the script will not be executed
directly. Instead, a new script will be generated by
replacing each %, and the character following it, with
information from the current event. The replacement depends
on the character following the %, as defined in the list
below. Unless otherwise indicated, the replacement string
is the decimal value of the given field from the current
event. 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.
%% Replaced with a single percent.
%# 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 hexade-
cimal 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 events other than these, the substituted string is
undefined.
%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 Con- |
figure and Expose events.
%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 events.
%q The fully-qualified access command for the window to |
which the event was reported. The %q field is like %W, |
but it reports the complete namespace path for the |
widget access command. It should be used instead of %W |
as the command name for the widget. Valid for all |
event types.
%s The state field from the event. For ButtonPress, But-
tonRelease, Enter, KeyPress, KeyRelease, Leave, and
Motion events, a decimal string is substituted. For
Visibility, one of the strings VisibilityUnobscured,
VisibilityPartiallyObscured, and VisibilityFullyOb-
scured 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 Config- |
ure and Expose events.
%x The x field from the event. Valid only for events con-
taining an x field.
%y The y field from the event. Valid only for events con-
taining a y field.
%A Substitutes the ASCII character corresponding to the
event, or the empty string if the event doesn't
correspond to an ASCII character (e.g. the shift key
was pressed). XLookupString does all the work of
translating from the event to an ASCII character.
Valid only for KeyPress and KeyRelease events.
%B The border_width field from the event. Valid only for
Configure events.
%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.
%M The window path name for the mega-widget containing the |
window which received the event. The %M field is like |
%Q, but it reports a Tk window name that can be used in |
conjunction with commands like pack and destroy. Valid |
for all event types.
%N The keysym corresponding to the event, substituted as a
decimal number. Valid only for KeyPress and KeyRelease
events.
%Q The fully-qualified access command for the mega-widget |
containing the window to which the event was reported. |
The %Q field is like %M, but it reports the complete |
namespace path for the mega-widget access command. It |
is useful for making generic bindings that are attached |
to mega-widget components but manipulate the mega- |
widget at a higher level when events are received. |
Valid for all event types.
%R The root window identifier from the event. Valid only
for events containing a root field.
%S The subwindow window identifier from the event, format-
ted 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 path name of the window to which the event was
reported (the window field from the event). 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.
The replacement string for a %-replacement is formatted as a
proper Tcl list element. This means that it will be sur-
rounded with braces if it contains spaces, or special char-
acters such as $ and { may be preceded by backslashes. This
guarantees that the string will be passed through the Tcl
parser when the binding script is evaluated. Most replace-
ments are numbers or well-defined strings such as Above;
for these replacements no special formatting is ever neces-
sary. The most common case where reformatting occurs is for
the %A substitution. For example, if script is
insert %A
and the character typed is an open square bracket, then the
script actually executed will be
insert \[
This will cause the insert to receive the original replace-
ment string (open square bracket) as its first argument. If
the extra backslash hadn't been added, Tcl would not have
been able to parse the script correctly.
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 binding for the widget will be executed first,
followed by a class binding, a binding for its toplevel, and
an all binding. The bindtags command may be used to change
this order for a particular window or to associate addi-
tional binding tags with the window.
The continue and break commands may be used inside a binding
script to control the processing of matching scripts. If
continue is invoked, then the current binding script is ter-
minated but Tk will continue processing binding scripts
associated with other tag's. If the break command is
invoked within a binding script, then that script terminates
and no other scripts will be invoked for the event. |
If more than one binding matches a particular event and they |
have the same tag, then the most specific binding is chosen |
and its script 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 vir- |
tual 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: |
event add <<Paste>> <Control-y> |
event add <<Paste>> <Button-2> |
event add <<Scroll>> <Button-2> |
bind Entry <<Paste>> {puts Paste} |
bind Entry <<Scroll>> {puts 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 command contains more
than one event pattern, then its script 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 script for a binding
then the bgerror mechanism is used to report the error. The
bgerror command will be executed at global level (outside
the context of any Tcl procedure).
SEE ALSO
bgerror
KEYWORDS
form, manual