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focus(3) |
User Contributed Perl Documentation |
focus(3) |
Tk::focus - Manage the input focus
$widget->focus
$widget->focusOption
$widget->focusNext
$widget->focusPrev
$widget->focusFollowsMouse
The focus methods are used to manage the Tk input focus. At any given
time, one window on each display is designated as the focus window; any
key press or key release events for the display are sent to that window. It is
normally up to the window manager to redirect the focus among the top-level
windows of a display. For example, some window managers automatically set the
input focus to a top-level window whenever the mouse enters it; others
redirect the input focus only when the user clicks on a window. Usually the
window manager will set the focus only to top-level windows, leaving it up to
the application to redirect the focus among the children of the top-level.
Tk remembers one focus window for each top-level (the most recent
descendant of that top-level to receive the focus); when the window manager
gives the focus to a top-level, Tk automatically redirects it to the
remembered window. Within a top-level Tk uses an explicit focus model
by default. Moving the mouse within a top-level does not normally change the
focus; the focus changes only when a widget decides explicitly to claim the
focus (e.g., because of a button click), or when the user types a key such
as Tab that moves the focus.
The method focusFollowsMouse may be invoked to create an
implicit focus model: it reconfigures Tk so that the focus is set to
a window whenever the mouse enters it. The methods focusNext and
focusPrev implement a focus order among the windows of a top-level;
they are used in the default bindings for Tab and Shift-Tab, among other
things.
The focus methods can take any of the following forms:
- $widget->focusCurrent
- Returns the focus window on the display containing the
$widget , or an empty string if no window in this
application has the focus on that display.
- $widget->focus
- If the application currently has the input focus on
$widget's display, this command resets the input
focus for $widget's display to
$widget and returns an empty string. If the
application doesn't currently have the input focus on
$widget 's display, $widget will
be remembered as the focus for its top-level; the next time the focus
arrives at the top-level, Tk will redirect it to
$widget.
- $widget->focusForce
- Sets the focus of $widget's display to
$widget, even if the application doesn't currently
have the input focus for the display. This command should be used
sparingly, if at all. In normal usage, an application should not claim the
focus for itself; instead, it should wait for the window manager to give
it the focus.
- $widget->focusLastfor
- Returns the name of the most recent window to have the input focus among
all the windows in the same top-level as $widget. If
no window in that top-level has ever had the input focus, or if the most
recent focus window has been deleted, then the top-level is returned. The
return value is the window that will receive the input focus the next time
the window manager gives the focus to the top-level.
- $widget->focusNext
- $widget->focusPrev
- focusNext is a utility method used for keyboard traversal, but can
be useful in other contexts. It sets the focus to the ``next'' window
after $widget in focus order. The focus order is
determined by the stacking order of windows and the structure of the
window hierarchy. Among siblings, the focus order is the same as the
stacking order, with the lowest window being first. If a window has
children, the window is visited first, followed by its children
(recursively), followed by its next sibling. Top-level windows other than
$widget are skipped, so that focusNext never
returns a window in a different top-level from
$widget.
After computing the next window, focusNext examines the
window's -takefocus option to see whether it should be skipped.
If so, focusNext continues on to the next window in the focus
order, until it eventually finds a window that will accept the focus or
returns back to $widget.
focusPrev is similar to focusNext except that it
sets the focus to the window just before $widget in
the focus order.
- $widget->focusFollowsMouse
- focusFollowsMouse changes the focus model for the application to an
implicit one where the window under the mouse gets the focus. After this
procedure is called, whenever the mouse enters a window Tk will
automatically give it the input focus. The focus command may be
used to move the focus to a window other than the one under the mouse, but
as soon as the mouse moves into a new window the focus will jump to that
window. Note: at present there is no built-in support for returning the
application to an explicit focus model; to do this you'll have to write a
script that deletes the bindings created by focusFollowsMouse.
When an internal window receives the input focus, Tk doesn't actually set the X
focus to that window; as far as X is concerned, the focus will stay on the
top-level window containing the window with the focus. However, Tk generates
FocusIn and FocusOut events just as if the X focus were on the internal
window. This approach gets around a number of problems that would occur if the
X focus were actually moved; the fact that the X focus is on the top-level is
invisible unless you use C code to query the X server directly.
Note that for the Canvas widget, the call to focus has to be fully
qualified. This is because there is already a focus method for the
Canvas widget, which sets the focus on individual canvas tags.
$canvas->Tk::focus
events, focus, keyboard, top-level, window manager
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