Clean up layer selection API

Author: dstansby

docs/changelog.rst

@@ -18,6 +18,9 @@ Changes
   you would be interested in please open an issue at https://github.com/matplotlib/napari-matplotlib.
 - Labels plotting with the features scatter widget no longer have underscores
   replaced with spaces.
+- ``NapariMPLWidget.update_layers()`` has been removed as it is intended to be
+  private API. Use `NapariMPLWidget.on_update_layers` instead to implement
+  funcitonality when layer selection is changed.
 
 Bug fixes
 ~~~~~~~~~

src/napari_matplotlib/base.py

@@ -34,6 +34,12 @@ class NapariMPLWidget(QWidget):
     advantage of this sub-classes should implement the ``clear()`` and
     ``draw()`` methods.
 
+    When both the z-step and layer selection is changed, ``clear()`` is called
+    and if the number a type of selected layers are valid for the widget
+    ``draw()`` is then called. When layer selection is changed ``on_update_layers()``
+    is also called, which can be useful e.g. for updating a layer list in a
+    selection widget.
+
     Attributes
     ----------
     viewer : `napari.Viewer`
@@ -103,14 +109,16 @@ def _setup_callbacks(self) -> None:
         # z-step changed in viewer
         self.viewer.dims.events.current_step.connect(self._draw)
         # Layer selection changed in viewer
-        self.viewer.layers.selection.events.changed.connect(self.update_layers)
+        self.viewer.layers.selection.events.changed.connect(
+            self._update_layers
+        )
 
-    def update_layers(self, event: napari.utils.events.Event) -> None:
+    def _update_layers(self, event: napari.utils.events.Event) -> None:
         """
         Update the ``layers`` attribute with currently selected layers and re-draw.
         """
         self.layers = list(self.viewer.layers.selection)
-        self._on_update_layers()
+        self.on_update_layers()
         self._draw()
 
     def _draw(self) -> None:
@@ -165,10 +173,9 @@ def apply_napari_colorscheme(ax: Axes) -> None:
         ax.tick_params(axis="x", colors="white")
         ax.tick_params(axis="y", colors="white")
 
-    def _on_update_layers(self) -> None:
+    def on_update_layers(self) -> None:
         """
-        Function is called when self.layers is updated via
-        ``self.update_layers()``.
+        Called when the selected layers are updated.
 
         This is a no-op, and is intended for derived classes to override.
         """

src/napari_matplotlib/histogram.py

@@ -27,7 +27,7 @@ def __init__(
     ):
         super().__init__(napari_viewer, parent=parent)
         self.add_single_axes()
-        self.update_layers(None)
+        self._update_layers(None)
 
     def clear(self) -> None:
         """

src/napari_matplotlib/scatter.py

@@ -132,7 +132,7 @@ def __init__(
             self.layout().addWidget(QLabel(f"{dim}-axis:"))
             self.layout().addWidget(self._selectors[dim])
 
-        self.update_layers(None)
+        self._update_layers(None)
 
     @property
     def x_axis_key(self) -> Union[str, None]:
@@ -230,7 +230,7 @@ def _get_data(self) -> Tuple[npt.NDArray[Any], npt.NDArray[Any], str, str]:
 
         return x, y, x_axis_name, y_axis_name
 
-    def _on_update_layers(self) -> None:
+    def on_update_layers(self) -> None:
         """
         Called when the layer selection changes by ``self.update_layers()``.
         """

src/napari_matplotlib/slice.py

@@ -51,7 +51,7 @@ def __init__(
         for d in _dims_sel:
             self.slice_selectors[d].textChanged.connect(self._draw)
 
-        self.update_layers(None)
+        self._update_layers(None)
 
     @property
     def _layer(self) -> napari.layers.Layer: