focus - Manage the input focus

SYNOPSIS

DESCRIPTION

The focus command is 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 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 Tcl procedure tk_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 Tcl procedures tk_focusNext and tk_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 command can take any of the following forms:

focus

Returns the path name of the focus window on the display containing the application's main window, or an empty string if no window in this application has the focus on that display. Note: it is better to specify the display explicitly using -displayof (see below) so that the code will work in applications using multiple displays.

focus window

Sets the input focus for window's display to window and returns an empty string. If window isn't viewable at the time this command is invoked, X will refuse to actually set the focus; nonetheless, window will be marked by Tk as the focus window for its display.

focus -displayof window

Returns the name of the focus window on the display containing window. If the focus window for window's display isn't in this application, the return value is an empty string.

focus -lastfor window

Returns the name of the most recent window to have the input focus among all the windows in the same top-level as window. 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 name of 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.

BUGS

When Tk redirects the input focus, either because of a focus command or because the window manager set the focus to a top-level and Tk is redirecting it to an internal window in the top-level, there may already be keyboard events queued. If this happens, the FocusIn and FocusOut events for the focus change will not be received until after the keyboard events; however, the keyboard events will be directed to the new focus window. This means that a window can receive keyboard events before receiving a FocusIn event.

KEYWORDS