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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 argument 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:
The sequence argument specifies a sequence
of one or more event patterns, with optional white space between the patterns.
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 pattern
is longer but more general. It has the following syntax:
<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) 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.
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.
Some widgets (e.g. menu and text) issue virtual events when their internal state is updated in some ways. Please see the manual page for each widget for details.
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
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.
The type field may be any of the
standard X event types, with a few extra abbreviations. The type field
will also accept a couple non-standard X event types that were added to
better support the Macintosh and Windows platforms. 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
When a mouse button is pressed, the window containing the pointer automatically obtains a temporary pointer grab. Subsequent ButtonPress, ButtonRelease, and Motion events will be sent to that window, regardless of which window contains the pointer, until all buttons have been released.
Windows are created in the unmapped state. Top-level windows become mapped when they transition to the normal state, and are unmapped in the withdrawn and iconic states. Other windows become mapped when they are placed under control of a geometry manager (for example pack or grid).
A window is viewable only if it and all of its ancestors are mapped. Note that geometry managers typically do not map their children until they have been mapped themselves, and unmap all children when they become unmapped; hence in Tk Map and Unmap events indicate whether or not a window is viewable.
When the Destroy event is delivered to a widget, it is in a ‘‘half-dead’’ state: the widget still exists, but most operations on it will fail.
In addition, if the old and new focus windows do not share a common parent, ‘‘virtual crossing’’ focus events are sent to the intermediate windows in the hierarchy. Thus a FocusIn event indicates that the target window or one of its descendants has acquired the focus, and a FocusOut event indicates that the focus has been changed to a window outside the target window’s hierarchy.
The keyboard focus may be changed explicitly by a call to focus, or implicitly by the window manager.
If there is a pointer grab in effect, Enter and Leave events are only delivered to the window owning the grab.
In addition, when the pointer moves between two windows, Enter and Leave ‘‘virtual crossing’’ events are sent to intermediate windows in the hierarchy in the same manner as for FocusIn and FocusOut events.
Widgets may be assigned a private colormap by specifying a -colormap option; the window manager is responsible for installing and uninstalling colormaps as necessary.
Note that Tk provides no useful details for this event type.
A Circulate event indicates that the window has moved to the top or to the bottom of the stacking order as a result of an XCirculateSubwindows protocol request. Note that the stacking order may be changed for other reasons which do not generate a Circulate event, and that Tk does not use XCirculateSubwindows() internally. This event type is included only for completeness; there is no reliable way to track changes to a window’s position in the stacking order.
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 keysym 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>.
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 command 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.
NotifyAncestor NotifyNonlinearVirtual
NotifyDetailNone NotifyPointer
NotifyInferior NotifyPointerRoot
NotifyNonlinear NotifyVirtual
Above Opposite
Below None
BottomIf TopIf
The replacement string for a %-replacement
is formatted as a proper Tcl list element. This means that it will be surrounded
with braces if it contains spaces, or special characters 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
replacements are numbers or well-defined strings such as Above; for these
replacements no special formatting is ever necessary. The most common case
where reformatting occurs is for the %A substitution. For example, if script
is
insert %Aand 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 replacement 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.
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 additional 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 terminated 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 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:
event add <<Paste>> <Control-y>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.
event add <<Paste>> <Button-2>
event add <<Scroll>> <Button-2>
bind Entry <<Paste>> {puts Paste}
bind Entry <<Scroll>> {puts Scroll}
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.
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.
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).
bind . <Double-1> {
puts "hi from (%x,%y)"
}
A little GUI that displays what the keysym name of the last key pressed
is: set keysym "Press any key"
pack [label .l -textvariable keysym -padx 2m -pady 1m]
bind . <Key> {
set keysym "You pressed %K"
}