The bind command associates Tcl scripts with X events. If all three arguments are specified, bind will arrange for script (a Tcl script called the ``binding 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 third form of pattern is used to specify a user-defined, named virtual event. It has the following syntax:
<<name>>
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:
ControlMod1, M1, Command Alt Mod2, M2, Option Shift Mod3, M3 Lock Mod4, M4 ExtendedMod5, M5 Button1, B1Meta, M Button2, B2Double Button3, B3Triple Button4, B4Quadruple Button5, B5
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.
The Command and Option modifiers are equivalents of Mod1 resp. Mod2, they correspond to Macintosh-specific modifier keys.
The Extended modifier is, at present, specific to Windows. It appears on events that are associated with the keys on the ``extended keyboard''. On a US keyboard, the extended keys include the Alt and Control keys at the right of the keyboard, the cursor keys in the cluster to the left of the numeric pad, the NumLock key, the Break key, the PrintScreen key, and the / and Enter keys in the numeric keypad.
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
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:
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 (e.g. ``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, called the ``binding 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.
NotifyAncestorNotifyNonlinearVirtual NotifyDetailNoneNotifyPointer NotifyInferiorNotifyPointerRoot NotifyNonlinearNotifyVirtual
For ConfigureRequest events, the string will be one of:
Above Opposite Below None BottomIfTopIf
For virtual events, the string will be whatever value is stored in the user_data field when the event was created (typically with event generate), or the empty string if the field is NULL. Virtual events corresponding to key sequence presses (see event add for details) set the user_data to NULL. For events other than these, the substituted string is undefined.
The replacement string for a %-replacement is formatted as a proper Tcl list element. This means that 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 %A
insert \[
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 within a binding script, then this binding script, including all other ``+'' appended scripts, 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.
Within a script called from the binding script, return -code ok may be used to continue processing (including ``+'' appended scripts), or return -code break may be used to stop processing all other binding scripts.
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:
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 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).
Arrange for a string describing the motion of the mouse to be printed out when the mouse is double-clicked:
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"
}