GNU bug report logs - #7381
24.0.50; Provide a hook run when a window is selected

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From: martin rudalics <rudalics <at> gmx.at>
To: Štěpán Němec <stepnem <at> gmail.com>,  7381 <at> debbugs.gnu.org
Subject: bug#7381: 24.0.50; Provide a hook run when a window is selected
Date: Sat, 12 Jan 2019 10:15:24 +0100

;; fixed 7381 27.1
;; quit

> The subject line says it all: could we get a `window-selected-hook' or
> `window-selected-functions' or something?
>
> Use case: I wanted to make myself a command to select the last selected
> window (i.e., repeating the command would toggle between two windows).
>
> After some head-scratching, the best I could come up with is this:
>
> (defun .goto-mru-window ()
>    (interactive)
>    (select-window (frame-parameter nil '.last-selected-window)))
>
> (defadvice select-window (before .save-selected-window activate)
>    (set-frame-parameter nil '.last-selected-window (selected-window)))
>
> ...which seems to work most of the time, but using an advice doesn't
> feel that great, esp. with C functions.

Current master now provides a hook run when redisplay detects that the
selected window has changed wrt last redisplay.  The hook is called
'window-selection-change-functions' and is described in detail in the
Elisp manual.  Below I sketch how that hook could be used to provide
the behavior you asked for.

martin


(defvar .old-selected-window (selected-window))

(defun .update-old-selected-window (frame)
  (unless (eq .update-old-selected-window old-selected-window)
    (setq .old-selected-window (old-selected-window))))

(add-hook 'window-selection-change-functions '.update-old-selected-window)

(defun .goto-mru-window ()
  (interactive)
  (select-window .old-selected-window))

(global-set-key [(control .)] '.goto-mru-window)

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