How do I bind a key to open or close a mode? (undo-tree)

Question

I'm using evil (via spacemacs) and I want to bind <f2> to open and close the undo-tree (like vim-Gundo). I can successfully bind opening undo-tree-visualize, but I can't figure out how to quit. I tried the obvious:

(define-key evil-normal-state-map (kbd "<f2>") 'undo-tree-visualizer)
(define-key undo-tree-visualizer-mode-map (kbd "<f2>") 'undo-tree-visualizer-quit)

It correctly opens undo-tree but doesn't close it (I get a "no undo information" error). I also tried to hook on load:

(defun my-undo-tree-hook ()
    (define-key undo-tree-visualizer-mode-map (kbd "<f2>") 'undo-tree-visualizer-quit))
(add-hook 'undo-tree-visualizer-mode-hook 'my-undo-tree-hook)

But that also doesn't work.

What am I doing wrong?

Answer 1

To get the same key to do different things in different contexts, bind it to a function that checks if the undo tree is open. You can use get-buffer[1] [2] to check for the undo-tree window and use the variable for the buffer name:

(defun undo-tree-visualizer-toggle ()
  (interactive)
  (if (get-buffer undo-tree-visualizer-buffer-name)
      (undo-tree-visualizer-quit)
    (undo-tree-visualize)))
;; You're usually in normal mode.
(define-key evil-normal-state-map (kbd "<f2>") 'undo-tree-visualizer-toggle)
;; Inside the undo-tree, you're in motion mode.
(define-key evil-motion-state-map (kbd "<f2>") 'undo-tree-visualizer-toggle)

You can find variables with C-h v (with helm I incrementally searched for "undo-tree buffer" to find it).