From 56504fae81c97fe04bfd378c0dad2dc94d221ca3 Mon Sep 17 00:00:00 2001
From: Elliott Sales de Andrade <quantum.analyst@gmail.com>
Date: Mon, 20 Apr 2020 18:12:55 -0400
Subject: [PATCH] Implement set_history_buttons for Tk toolbar.

This makes the backward/forward buttons change enabled state based on
whether there are actually old/new views available.
---
 lib/matplotlib/backends/_backend_tk.py | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/lib/matplotlib/backends/_backend_tk.py b/lib/matplotlib/backends/_backend_tk.py
index 2170c93f77c3..ef655853b492 100644
--- a/lib/matplotlib/backends/_backend_tk.py
+++ b/lib/matplotlib/backends/_backend_tk.py
@@ -620,6 +620,16 @@ def save_figure(self, *args):
         except Exception as e:
             tkinter.messagebox.showerror("Error saving file", str(e))
 
+    def set_history_buttons(self):
+        if self._nav_stack._pos > 0:
+            self._buttons['Back']['state'] = tk.NORMAL
+        else:
+            self._buttons['Back']['state'] = tk.DISABLED
+        if self._nav_stack._pos < len(self._nav_stack._elements) - 1:
+            self._buttons['Forward']['state'] = tk.NORMAL
+        else:
+            self._buttons['Forward']['state'] = tk.DISABLED
+
 
 class ToolTip:
     """