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blt::busy(3tcl) BLT Built-In Commands blt::busy(3tcl)


busy - Make Tk widgets busy, temporarily blocking user interactions.


busy hold window ?option value?...

busy release window ?window?...

busy configure window ?option value?...

busy forget window ?window?...

busy isbusy ?pattern?

busy names ?pattern?

busy status window


The busy command provides a simple means to block keyboard, button, and pointer events from Tk widgets, while overriding the widget's cursor with a configurable busy cursor.


There are many times in applications where you want to temporarily restrict what actions the user can take. For example, an application could have a "run" button that when pressed causes some processing to occur. But while the application is busy processing, you probably don't want the 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 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 descendents will ignore 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 busy command can be used instead of Tk's grab command. Unlike grab which restricts all user interactions to one widget, with the busy command you can have more than one widget active (for example, a "cancel" dialog and a "help" button).


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
  . . .
busy hold .top

All the widgets within .top (including .top) are now busy. Using update insures that 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 by the release operation.

	busy release .top 
The busy window has a configurable cursor. You can change the busy cursor using the configure operation.
	busy configure .top -cursor "watch"
Finally, when you no longer need to the busy window, invoke the forget operation to free any resources it allocated.
	busy forget .top 
Destroying the widget will also clean up any resources allocated by the busy command.


The following operations are available for the busy command:
busy hold window ?option value?...
Makes the widget window (and its descendants in the Tk window hierarchy) busy. Window must be a valid path name of a Tk widget. The busy window is mapped the next time idle tasks are processed, and the widget and its descendants will be blocked from user interactions. All events in the widget window and its descendants are ignored. Normally update should be called immediately afterward to insure that the hold operation is in effect before the application starts its processing. 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 watch.
busy configure window ?option value?...
Queries or modifies the 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 option(s) to have the given value(s); in this case the command returns the empty string. Option may have any of the values accepted by the hold operation.

Please note that the option database is referenced through window. 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
busy forget window ?window?...
Releases resources allocated by the busy command for window, including the busy window. User events will again be received again by window. Resources are also released when window is destroyed. Window must be the name of a widget specified in the hold operation, otherwise an error is reported.
busy isbusy ?pattern?
Returns the pathnames of all widgets that are currently busy. If a pattern is given, the path names of busy widgets matching pattern are returned.
busy names ?pattern?
Returns the pathnames of all widgets that have previously been made busy (i.e. a busy window is allocated and associated with the widget). It makes no difference if the window is currently busy or not. If a pattern is given, the path names of busy widgets matching pattern are returned.
busy release window ?window?...
Restores user interactions to the widget window again. This differs from the forget operation in that the busy window is not destroyed, but simply unmapped. Window must be the name of a widget specified in a hold operation, otherwise an error is reported.
busy status window
Returns the status of a widget window previously made busy. An error is reported if window was never made busy, or the forget operation was invoked (i.e. does not currently have a busy window associated with it). If window is presently can not receive user interactions, 1 is returned, otherwise 0.


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.

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 "widget._Busy" where widget is the name of the toplevel widget. In the following example, the pathname of the busy window is "._Busy"

busy hold .
bind ._Busy <Enter> { ... } 


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.


When a widget is made busy, the widget is prevented from gaining the keyboard focus by the busy window. But if the widget already had focus, it still may received keyboard events. To prevent this, you must move focus to another window.

busy hold .frame
label .dummy
focus .dummy

The above example moves the focus from .frame immediately after invoking the hold so that no keyboard events will be sent to .frame or any of its descendants.


busy, keyboard events, pointer events, window, cursor

2.5 BLT