Use _Backend from matplotlib to simplify the code

.gitignore

@@ -13,3 +13,6 @@ js/*.tgz
 
 # OS X
 .DS_Store
+
+# vscode
+.vscode/

ipympl/backend_nbagg.py

@@ -13,13 +13,13 @@
 )
 
 from matplotlib import rcParams
-from matplotlib.figure import Figure
 from matplotlib import is_interactive
 from matplotlib.backends.backend_webagg_core import (FigureManagerWebAgg,
                                                      FigureCanvasWebAggCore,
                                                      NavigationToolbar2WebAgg,
                                                      TimerTornado)
-from matplotlib.backend_bases import ShowBase, NavigationToolbar2, cursors
+from matplotlib.backend_bases import NavigationToolbar2, cursors, _Backend
+from matplotlib._pylab_helpers import Gcf
 
 from ._version import js_semver
 
@@ -32,43 +32,6 @@
 }
 
 
-class Show(ShowBase):
-
-    def __call__(self, block=None):
-        from matplotlib._pylab_helpers import Gcf
-
-        managers = Gcf.get_all_fig_managers()
-        if not managers:
-            return
-
-        interactive = is_interactive()
-
-        for manager in managers:
-            manager.show()
-
-            # plt.figure adds an event which puts the figure in focus
-            # in the activeQue. Disable this behaviour, as it results in
-            # figures being put as the active figure after they have been
-            # shown, even in non-interactive mode.
-            if hasattr(manager, '_cidgcf'):
-                manager.canvas.mpl_disconnect(manager._cidgcf)
-
-            if not interactive and manager in Gcf._activeQue:
-                Gcf._activeQue.remove(manager)
-
-
-show = Show()
-
-
-def draw_if_interactive():
-    import matplotlib._pylab_helpers as pylab_helpers
-
-    if is_interactive():
-        manager = pylab_helpers.Gcf.get_active()
-        if manager is not None:
-            manager.show()
-
-
 def connection_info():
     """
     Return a string showing the figure and connection status for
@@ -260,33 +223,47 @@ def destroy(self):
         self.canvas.close()
 
 
-def new_figure_manager(num, *args, **kwargs):
-    """
-    Create a new figure manager instance
-    """
-    figure_class = kwargs.pop('FigureClass', Figure)
-    this_fig = figure_class(*args, **kwargs)
-    return new_figure_manager_given_figure(num, this_fig)
+@_Backend.export
+class _Backend_ipympl(_Backend):
+    FigureCanvas = Canvas
+    FigureManager = FigureManager
 
+    @staticmethod
+    def new_figure_manager_given_figure(num, figure):
+        canvas = Canvas(figure)
+        if 'nbagg.transparent' in rcParams and rcParams['nbagg.transparent']:
+            figure.patch.set_alpha(0)
+        manager = FigureManager(canvas, num)
+        if is_interactive():
+            manager.show()
+            figure.canvas.draw_idle()
 
-def new_figure_manager_given_figure(num, figure):
-    """
-    Create a new figure manager instance for the given figure.
-    """
-    from matplotlib._pylab_helpers import Gcf
+        def destroy(event):
+            canvas.mpl_disconnect(cid)
+            Gcf.destroy(manager)
 
-    def closer(event):
-        Gcf.destroy(num)
+        cid = canvas.mpl_connect('close_event', destroy)
+        return manager
 
-    canvas = Canvas(figure)
-    if 'nbagg.transparent' in rcParams and rcParams['nbagg.transparent']:
-        figure.patch.set_alpha(0)
-    manager = FigureManager(canvas, num)
+    @staticmethod
+    def show(block=None):
+        # TODO: something to do when keyword block==False ?
 
-    if is_interactive():
-        manager.show()
-        figure.canvas.draw_idle()
+        managers = Gcf.get_all_fig_managers()
+        if not managers:
+            return
+
+        interactive = is_interactive()
+
+        for manager in managers:
+            manager.show()
 
-    canvas.mpl_connect('close_event', closer)
+            # plt.figure adds an event which makes the figure in focus the
+            # active one. Disable this behaviour, as it results in
+            # figures being put as the active figure after they have been
+            # shown, even in non-interactive mode.
+            if hasattr(manager, '_cidgcf'):
+                manager.canvas.mpl_disconnect(manager._cidgcf)
 
-    return manager
+            if not interactive:
+                Gcf.figs.pop(manager.num, None)

pyproject.toml

@@ -1,3 +1,15 @@
 [build-system]
 requires = ["jupyter_packaging~=0.7.0", "jupyterlab>=3.0.0,==3.*", "setuptools>=40.8.0", "wheel"]
 build-backend = "setuptools.build_meta"
+
+
+[tool.pytest.ini_options]
+testpaths = [
+    "test-notebooks",
+    "examples",
+]
+norecursedirs = [
+    "node_modules",
+    ".ipynb_checkpoints",
+]
+addopts = "--nbval --current-env"

test-notebooks/UAT.ipynb

@@ -0,0 +1,92 @@
+{
+ "cells": [
+  {
+   "cell_type": "markdown",
+   "id": "antique-treasure",
+   "metadata": {},
+   "source": [
+    "# User Automated Testing\n",
+    "\n",
+    "A notebook to run manually to catch issues with the backend."
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "binary-speaker",
+   "metadata": {},
+   "source": [
+    "# 1. Checking plt.show()\n",
+    "\n",
+    "The implementation of plt.show relies on the private `matplotlib._pylab_helpers.Gcf` which can break (https://github.com/matplotlib/ipympl/issues/303). The cell should run without any errors."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "agricultural-whole",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "%matplotlib ipympl\n",
+    "import matplotlib.pyplot as plt\n",
+    "plt.ioff()\n",
+    "fig = plt.figure()\n",
+    "plt.plot([0,1],[0,1])\n",
+    "plt.show()"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "secure-consistency",
+   "metadata": {},
+   "source": [
+    "# 2 plt.close()\n",
+    "\n",
+    "Calling `plt.close()` should prevent further interactions with the figure - so panning and resizing should no longer work after the second cell in this test."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "hollow-front",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "plt.ion()\n",
+    "plt.figure()\n",
+    "plt.plot([0,1],[0,1])\n"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "classical-pavilion",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "plt.close()"
+   ]
+  }
+ ],
+ "metadata": {
+  "kernelspec": {
+   "display_name": "Python 3",
+   "language": "python",
+   "name": "python3"
+  },
+  "language_info": {
+   "codemirror_mode": {
+    "name": "ipython",
+    "version": 3
+   },
+   "file_extension": ".py",
+   "mimetype": "text/x-python",
+   "name": "python",
+   "nbconvert_exporter": "python",
+   "pygments_lexer": "ipython3",
+   "version": "3.9.2"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 5
+}