1focus(n)                     Tk Built-In Commands                     focus(n)
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NAME

8       focus - Manage the input focus
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SYNOPSIS

11       focus
12       focus window
13       focus option ?arg arg ...?
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DESCRIPTION

17       The  focus  command is used to manage the Tk input focus.  At any given
18       time, one window on each display is designated  as  the  focus  window;
19       any  key  press  or key release events for the display are sent to that
20       window.  It is normally up to the window manager to redirect the  focus
21       among  the  top-level  windows  of a display.  For example, some window
22       managers automatically set the input focus to a top-level window  when‐
23       ever  the  mouse  enters it;  others redirect the input focus only when
24       the user clicks on a window.  Usually the window manager will  set  the
25       focus  only  to  top-level windows, leaving it up to the application to
26       redirect the focus among the children of the top-level.
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28       Tk remembers one focus window  for  each  top-level  (the  most  recent
29       descendant  of  that  top-level to receive the focus);  when the window
30       manager gives the focus to a top-level, Tk automatically  redirects  it
31       to the remembered window.  Within a top-level Tk uses an explicit focus
32       model by default.  Moving the mouse within a top-level  does  not  nor‐
33       mally  change  the focus;  the focus changes only when a widget decides
34       explicitly to claim the focus (e.g., because of  a  button  click),  or
35       when the user types a key such as Tab that moves the focus.
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37       The  Tcl  procedure  tk_focusFollowsMouse  may  be invoked to create an
38       implicit focus model:  it reconfigures Tk so that the focus is set to a
39       window  whenever  the mouse enters it.  The Tcl procedures tk_focusNext
40       and tk_focusPrev implement a focus order among the windows  of  a  top-
41       level;   they  are  used in the default bindings for Tab and Shift-Tab,
42       among other things.
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44       The focus command can take any of the following forms:
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46       focus  Returns the path name of the focus window on  the  display  con‐
47              taining the application's main window,  or an empty string if no
48              window in this  application  has  the  focus  on  that  display.
49              Note:   it  is  better  to  specify the display explicitly using
50              -displayof (see below) so that the code will  work  in  applica‐
51              tions using multiple displays.
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53       focus window
54              If  the  application  currently  has the input focus on window's
55              display, this command resets the input focus for  window's  dis‐
56              play  to window and returns an empty string.  If the application
57              does not currently have the input  focus  on  window's  display,
58              window  will  be remembered as the focus for its top-level;  the
59              next time the focus arrives at the top-level, Tk  will  redirect
60              it  to  window.   If  window is an empty string then the command
61              does nothing.
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63       focus -displayof window
64              Returns the name of the focus window on the  display  containing
65              window.  If the focus window for window's display is not in this
66              application, the return value is an empty string.
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68       focus -force window
69              Sets the focus of window's display to window, even if the appli‐
70              cation  does not currently have the input focus for the display.
71              This command should be used sparingly, if  at  all.   In  normal
72              usage,  an  application  should  not claim the focus for itself;
73              instead, it should wait for the window manager to  give  it  the
74              focus.  If window is an empty string then the command does noth‐
75              ing.
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77       focus -lastfor window
78              Returns the name of the most recent window  to  have  the  input
79              focus among all the windows in the same top-level as window.  If
80              no window in that top-level has ever had the input focus, or  if
81              the  most recent focus window has been deleted, then the name of
82              the top-level is returned.  The return value is the window  that
83              will  receive  the  input focus the next time the window manager
84              gives the focus to the top-level.
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QUIRKS

87       When an internal window receives the input focus, Tk does not  actually
88       set  the  X  focus to that window;  as far as X is concerned, the focus
89       will stay on the top-level window containing the window with the focus.
90       However,  Tk  generates  FocusIn  and  FocusOut events just as if the X
91       focus were on the internal window.   This approach gets around a number
92       of  problems  that  would occur if the X focus were actually moved; the
93       fact that the X focus is on the top-level is invisible unless you use C
94       code to query the X server directly.
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EXAMPLE

97       To  make  a  window  that only participates in the focus traversal ring
98       when a variable is set, add  the  following  bindings  to  the  widgets
99       before and after it in that focus ring:
100              button .before -text "Before"
101              button .middle -text "Middle"
102              button .after  -text "After"
103              checkbutton .flag -variable traverseToMiddle -takefocus 0
104              pack .flag -side left
105              pack .before .middle .after
106              bind .before <Tab> {
107                 if {!$traverseToMiddle} {
108                    focus .after
109                    break
110                 }
111              }
112              bind .after <Shift-Tab> {
113                 if {!$traverseToMiddle} {
114                    focus .before
115                    break
116                 }
117              }
118              focus .before
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KEYWORDS

121       events, focus, keyboard, top-level, window manager
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125Tk                                    4.0                             focus(n)
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