1focus(3)              User Contributed Perl Documentation             focus(3)
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NAME

6       Tk::focus - Manage the input focus
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SYNOPSIS

9          $widget->focus
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11          $widget->focusOption
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13          $widget->focusNext
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15          $widget->focusPrev
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17          $widget->focusFollowsMouse
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DESCRIPTION

20       The focus methods are used to manage the Tk input focus.  At any given
21       time, one window on each display is designated as the focus window;
22       any key press or key release events for the display are sent to that
23       window.  It is normally up to the window manager to redirect the focus
24       among the top-level windows of a display.  For example, some window
25       managers automatically set the input focus to a top-level window
26       whenever the mouse enters it;  others redirect the input focus only
27       when the user clicks on a window.  Usually the window manager will set
28       the focus only to top-level windows, leaving it up to the application
29       to redirect the focus among the children of the top-level.
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31       Tk remembers one focus window for each top-level (the most recent
32       descendant of that top-level to receive the focus);  when the window
33       manager gives the focus to a top-level, Tk automatically redirects it
34       to the remembered window.  Within a top-level Tk uses an explicit focus
35       model by default.  Moving the mouse within a top-level does not
36       normally change the focus;  the focus changes only when a widget
37       decides explicitly to claim the focus (e.g., because of a button
38       click), or when the user types a key such as Tab that moves the focus.
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40       The method focusFollowsMouse may be invoked to create an implicit focus
41       model:  it reconfigures Tk so that the focus is set to a window
42       whenever the mouse enters it.  The methods focusNext and focusPrev
43       implement a focus order among the windows of a top-level;  they are
44       used in the default bindings for Tab and Shift-Tab, among other things.
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46       The focus methods can take any of the following forms:
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48       $widget->focusCurrent
49           Returns the focus window on the display containing the $widget,  or
50           an empty string if no window in this application has the focus on
51           that display.
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53       $widget->focus
54           If the application currently has the input focus on $widget's
55           display, this command resets the input focus for $widget's display
56           to $widget and returns an empty string.  If the application doesn't
57           currently have the  input focus on $widget's display, $widget will
58           be remembered as the focus for its top-level;  the next time the
59           focus arrives at the top-level, Tk will redirect it to $widget.
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61       $widget->focusForce
62           Sets the focus of $widget's display to $widget, even if the
63           application doesn't currently have the input focus for the display.
64           This command should be used sparingly, if at all.  In normal usage,
65           an application should not claim the focus for itself;  instead, it
66           should wait for the window manager to give it the focus.
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68       $widget->focusLastfor
69           Returns the name of the most recent window to have the input focus
70           among all the windows in the same top-level as $widget.  If no
71           window in that top-level has ever had the input focus, or if the
72           most recent focus window has been deleted, then the top-level is
73           returned.  The return value is the window that will receive the
74           input focus the next time the window manager gives the focus to the
75           top-level.
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77       $widget->focusNext
78       $widget->focusPrev
79           focusNext is a utility method used for keyboard traversal, but can
80           be useful in other contexts.  It sets the focus to the ``next''
81           window after $widget in focus order.  The focus order is determined
82           by the stacking order of windows and the structure of the window
83           hierarchy.  Among siblings, the focus order is the same as the
84           stacking order, with the lowest window being first.  If a window
85           has children, the window is visited first, followed by its children
86           (recursively), followed by its next sibling.  Top-level windows
87           other than $widget are skipped, so that focusNext never returns a
88           window in a different top-level from $widget.
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90           After computing the next window, focusNext examines the window's
91           -takefocus option to see whether it should be skipped.  If so,
92           focusNext continues on to the next window in the focus order, until
93           it eventually finds a window that will accept the focus or returns
94           back to $widget.
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96           focusPrev is similar to focusNext except that it sets the focus to
97           the window just before $widget in the focus order.
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99       $widget->focusFollowsMouse
100           focusFollowsMouse changes the focus model for the application to an
101           implicit one where the window under the mouse gets the focus.
102           After this procedure is called, whenever the mouse enters a window
103           Tk will automatically give it the input focus.  The focus command
104           may be used to move the focus to a window other than the one under
105           the mouse, but as soon as the mouse moves into a new window the
106           focus will jump to that window.  Note: at present there is no
107           built-in support for returning the application to an explicit focus
108           model;  to do this you'll have to write a script that deletes the
109           bindings created by focusFollowsMouse.
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QUIRKS

112       When an internal window receives the input focus, Tk doesn't actually
113       set the X focus to that window;  as far as X is concerned, the focus
114       will stay on the top-level window containing the window with the focus.
115       However, Tk generates FocusIn and FocusOut events just as if the X
116       focus were on the internal window.   This approach gets around a number
117       of problems that would occur if the X focus were actually moved; the
118       fact that the X focus is on the top-level is invisible unless you use C
119       code to query the X server directly.
120

CAVEATS

122       Note that for the Canvas widget, the call to focus has to be fully
123       qualified. This is because there is already a focus method for the
124       Canvas widget, which sets the focus on individual canvas tags.
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126           $canvas->Tk::focus
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KEYWORDS

129       events, focus, keyboard, top-level, window manager
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133perl v5.32.0                      2020-07-28                          focus(3)
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