busy(3tk) Tk Built-In Commands busy(3tk)
______________________________________________________________________________
NAME
busy - confine pointer events to a window sub-tree
SYNOPSIS
tk busy window ?options?
tk busy hold window ?options?
tk busy configure window ?option value?...
tk busy forget window ?window ?...
tk busy current ?pattern?
tk busy status window
______________________________________________________________________________
DESCRIPTION
The tk busy command provides a simple means to block pointer events
from Tk widgets, while overriding the widget's cursor with a config-
urable busy cursor. Note this command does not prevent keyboard events
from being sent to the widgets made busy.
INTRODUCTION
There are many times in applications where you want to temporarily re-
strict what actions the user can take. For example, an application
could have a “Run” button that when pressed causes some processing to
occur. However, while the application is busy processing, you probably
don't want the user to be able to click the “Run” button again. You may
also want restrict the user from other tasks such as clicking a “Print”
button.
The tk busy command lets you make Tk widgets busy. This means that user
interactions such as button clicks, moving the mouse, typing at the
keyboard, etc. are ignored by the widget. You can set a special cursor
(like a watch) that overrides the widget's normal cursor, providing
feedback that the application (widget) is temporarily busy.
When a widget is made busy, the widget and all of its descendants will
ignore pointer events. It's easy to make an entire panel of widgets
busy. You can simply make the toplevel widget (such as “.”) busy. This
is easier and far much more efficient than recursively traversing the
widget hierarchy, disabling each widget and re-configuring its cursor.
Often, the tk busy command can be used instead of Tk's grab command.
Unlike grab which restricts all user interactions to one widget, with
the tk busy command you can have more than one widget active (for exam-
ple, a “Cancel” dialog and a “Help” button).
EXAMPLE
You can make several widgets busy by simply making its ancestor widget
busy using the hold operation.
frame .top
button .top.button; canvas .top.canvas
pack .top.button .top.canvas
pack .top
# . . .
tk busy hold .top
update
All the widgets within .top (including .top) are now busy. Using update
insures that tk busy command will take effect before any other user
events can occur.
When the application is no longer busy processing, you can allow user
interactions again and free any resources it allocated by the forget
operation.
tk busy forget .top
The busy window has a configurable cursor. You can change the busy cur-
sor using the configure operation.
tk busy configure .top -cursor "watch"
Destroying the widget will also clean up any resources allocated by the
tk busy command.
OPERATIONS
The following operations are available for the tk busy command:
tk busy window ?option value?...
Shortcut for tk busy hold command.
tk busy hold window ?option value?...
Makes the specified window (and its descendants in the Tk window
hierarchy) appear busy. Window must be a valid path name of a Tk
widget. A transparent window is put in front of the specified
window. This transparent window is mapped the next time idle
tasks are processed, and the specified window and its descen-
dants will be blocked from user interactions. Normally update
should be called immediately afterward to insure that the hold
operation is in effect before the application starts its pro-
cessing. The following configuration options are valid:
-cursor cursorName
Specifies the cursor to be displayed when the widget is
made busy. CursorName can be in any form accepted by
Tk_GetCursor. The default cursor is wait on Windows and
watch on other platforms.
tk busy cget window option
Queries the tk busy command configuration options for window.
Window must be the path name of a widget previously made busy by
the hold operation. The command returns the present value of the
specified option. Option may have any of the values accepted by
the hold operation.
tk busy configure window ?option value?...
Queries or modifies the tk busy command configuration options
for window. Window must be the path name of a widget previously
made busy by the hold operation. If no options are specified, a
list describing all of the available options for window (see
Tk_ConfigureInfo for information on the format of this list) is
returned. If option is specified with no value, then the command
returns a list describing the one named option (this list will
be identical to the corresponding sublist of the value returned
if no option is specified). If one or more option-value pairs
are specified, then the command modifies the given widget op-
tion(s) to have the given value(s); in this case the command re-
turns the empty string. Option may have any of the values ac-
cepted by the hold operation.
Please note that the option database is referenced through win-
dow. For example, if the widget .frame is to be made busy, the
busy cursor can be specified for it by either option command:
option add *frame.busyCursor gumby
option add *Frame.BusyCursor gumby
tk busy forget window ?window?...
Releases resources allocated by the tk busy command for window,
including the transparent window. User events will again be re-
ceived by window. Resources are also released when window is de-
stroyed. Window must be the name of a widget specified in the
hold operation, otherwise an error is reported.
tk busy current ?pattern?
Returns the pathnames of all widgets that are currently busy. If
a pattern is given, only the path names of busy widgets matching
pattern are returned.
tk busy status window
Returns the status of a widget window. If window presently can
not receive user interactions, 1 is returned, otherwise 0.
EVENT HANDLING
BINDINGS
The event blocking feature is implemented by creating and mapping a
transparent window that completely covers the widget. When the busy
window is mapped, it invisibly shields the widget and its hierarchy
from all events that may be sent. Like Tk widgets, busy windows have
widget names in the Tk window hierarchy. This means that you can use
the bind command, to handle events in the busy window.
tk busy hold .frame.canvas
bind .frame.canvas_Busy <Enter> { ... }
Normally the busy window is a sibling of the widget. The name of the
busy window is “widget_Busy” where widget is the name of the widget to
be made busy. In the previous example, the pathname of the busy window
is “.frame.canvas_Busy”. The exception is when the widget is a
toplevel widget (such as “.”) where the busy window can't be made a
sibling. The busy window is then a child of the widget named “wid-
get._Busy” where widget is the name of the toplevel widget. In the fol-
lowing example, the pathname of the busy window is “._Busy”.
tk busy hold .
bind ._Busy <Enter> { ... }
ENTER/LEAVE EVENTS
Mapping and unmapping busy windows generates Enter/Leave events for all
widgets they cover. Please note this if you are tracking Enter/Leave
events in widgets.
KEYBOARD EVENTS
When a widget is made busy, the widget is prevented from gaining the
keyboard focus by a user clicking on it by the busy window. But if the
widget already had focus, it still may receive keyboard events. The
widget can also still receive focus through keyboard traversal. To pre-
vent this, you must move focus to another window and make sure the fo-
cus can not go back to the widgets made busy (e.g. but restricting fo-
cus to a cancel button).
pack [frame .frame]
pack [text .frame.text]
tk busy hold .frame
pack [button .cancel -text "Cancel" -command exit]
focus .cancel
bind .cancel <Tab> {break}
bind .cancel <Shift-Tab> {break}
update
The above example moves the focus from .frame immediately after invok-
ing the hold so that no keyboard events will be sent to .frame or any
of its descendants. It also makes sure it's not possible to leave but-
ton .cancel using the keyboard.
PORTABILITY
Note that the tk busy command does not currently have any effect on OSX
when Tk is built using Aqua support.
SEE ALSO
grab(3tk)
KEYWORDS
busy, keyboard events, pointer events, window
Tk busy(3tk)
Generated by dwww version 1.14 on Fri Jul 18 10:17:49 CEST 2025.