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bind(3) 		       User Contributed Perl Documentation			  bind(3)

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 v5.16.3				    2014-06-10					  bind(3)
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