102 lines
5.0 KiB
HTML
102 lines
5.0 KiB
HTML
<HTML><HEAD><TITLE>Tk Built-In Commands - focus manual page</TITLE></HEAD>
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<BODY bgcolor = #c3c3ff>
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<H2><IMG ALIGN=BOTTOM SRC="./Img/ManPageBlue.gif"> focus</H2>
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<I>Manage the input focus</I><P><IMG ALIGN=TOP SRC="./Img/line-red.gif">
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<H3><A NAME="M2">SYNOPSIS</A></H3>
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(<B>focus</B>)<BR>
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(<B>focus </B><I>window</I>)<BR>
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(<B>focus </B><I>option</I> ?<I>arg arg ...</I>?)<BR>
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<H3><A NAME="M3">DESCRIPTION</A></H3>
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The <B>focus</B> procedure is used to manage the Tk input focus.
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At any given time, one window on each display is designated as
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the <I>focus window</I>; any key press or key release events for the
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display are sent to that window.
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It is normally up to the window manager to redirect the focus among the
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top-level windows of a display. For example, some window managers
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automatically set the input focus to a top-level window whenever
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the mouse enters it; others redirect the input focus only when
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the user clicks on a window.
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Usually the window manager will set the focus
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only to top-level windows, leaving it up to the application to
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redirect the focus among the children of the top-level.
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<P>
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Tk remembers one focus window for each top-level (the most recent
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descendant of that top-level to receive the focus); when the window
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manager gives the focus
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to a top-level, Tk automatically redirects it to the remembered
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window. Within a top-level Tk uses an <I>explicit</I> focus model
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by default. Moving the mouse within a top-level does not normally
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change the focus; the focus changes only when a widget
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decides explicitly to claim the focus (e.g., because of a button
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click), or when the user types a key such as Tab that moves the
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focus.
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<P>
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The STk procedure <B>Tk:focus-follows-mouse</B> may be invoked to
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create an <I>implicit</I> focus model: it reconfigures Tk so that
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the focus is set to a window whenever the mouse enters it.
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The STk procedures <B>Tk:focus-next</B> and <B> Tk:focus-prev</B>
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implement a focus order among the windows of a top-level; they
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are used in the default bindings for Tab and Shift-Tab, among other
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things.
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<P>
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The <B>focus</B> procedure can take any of the following forms:
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<P>
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<DL>
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<DT><A NAME="M4">(<B>focus</B>)</A><DD>
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Returns the path name of the focus window on the display containing
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the application's main window, or <B>#f</B> if no window in
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this application has the focus on that display. Note: it is
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better to specify the display explicitly using <B>:displayof</B>
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(see below) so that the code will work in applications using multiple
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displays.
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<P>
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<DT><A NAME="M5">(<B>focus </B><I>window</I>)</A><DD>
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If the application currently has the input focus on <I>window</I>'s
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display, this procedure resets the input focus for <I>window</I>'s display
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to <I>window</I> and returns an empty string.
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If the application doesn't currently have the input focus on
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<I>window</I>'s display, <I>window</I> will be remembered as the focus
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for its top-level; the next time the focus arrives at the top-level,
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Tk will redirect it to <I>window</I>.
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If <I>window</I> is an empty string then the procedure does nothing.
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<P>
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<DT><A NAME="M6">(<B>focus :displayof</B> <I>window</I>)</A><DD>
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Returns the name of the focus window on the display containing <I>window</I>.
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If the focus window for <I>window</I>'s display isn't in this
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application, the return value is an empty list.
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<P>
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<DT><A NAME="M7">(<B>focus :force </B><I>window</I>)</A><DD>
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Sets the focus of <I>window</I>'s display to <I>window</I>, even if
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the application doesn't currently have the input focus for the display.
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This procedure should be used sparingly, if at all.
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In normal usage, an application should not claim the focus for
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itself; instead, it should wait for the window manager to give it
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the focus.
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If <I>window</I> is an empty string then the procedure does nothing.
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<P>
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<DT><A NAME="M8">(<B>focus :lastfor</B> <I>window</I>)</A><DD>
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Returns the name of the most recent window to have the input focus
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among all the windows in the same top-level as <I>window</I>.
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If no window in that top-level has ever had the input focus, or
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if the most recent focus window has been deleted, then the name
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of the top-level is returned. The return value is the window that
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will receive the input focus the next time the window manager gives
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the focus to the top-level.
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<P>
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</DL>
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<H3><A NAME="M9">QUIRKS</A></H3>
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When an internal window receives the input focus, Tk doesn't actually
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set the X focus to that window; as far as X is concerned, the focus
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will stay on the top-level window containing the window with the focus.
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However, Tk generates FocusIn and FocusOut events just as if the X
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focus were on the internal window. This approach gets around a
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number of problems that would occur if the X focus were actually moved;
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the fact that the X focus is on the top-level is invisible unless
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you use C code to query the X server directly.
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<H3><A NAME="M10">SEE ALSO</A></H3>
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<B><A HREF="./grab.n.html">grab</A></B>
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<P><IMG ALIGN=TOP SRC="./Img/line-red.gif">
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<A HREF=./STk-hlp.html><IMG ALIGN=BOTTOM SRC="./Img/RefBookBlue.gif"> Back to the <B>STk</B> main page</A>
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</BODY></HTML>
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