support creating new instances of plugins, independent of tray

* move logic for assigning default viewer references from the app-method to the plugin itself, by searching the registry for a match
* create "new" convenience method on plugin
* allows for running results from a saved plugin state without altering the user-facing instance of the plugin

jdaviz/app.py

@@ -2509,29 +2509,8 @@ def compose_viewer_area(viewer_area_items):
 
         for name in config.get('tray', []):
             tray = tray_registry.members.get(name)
-            tray_registry_options = tray.get('viewer_reference_name_kwargs', {})
-
-            # Optional keyword arguments are required to initialize some
-            # tray items. These kwargs specify the viewer reference names that are
-            # assumed to be present in the configuration.
-            optional_tray_kwargs = dict()
-
-            # If viewer reference names need to be passed to the tray item
-            # constructor, pass the names into the constructor in the format
-            # that the tray items expect.
-            for opt_attr, [opt_kwarg, get_name_kwargs] in tray_registry_options.items():
-                opt_value = getattr(
-                    self, opt_attr, self._get_first_viewer_reference_name(**get_name_kwargs)
-                )
-
-                if opt_value is None:
-                    continue
-
-                optional_tray_kwargs[opt_kwarg] = opt_value
 
-            tray_item_instance = tray.get('cls')(
-                app=self, **optional_tray_kwargs
-            )
+            tray_item_instance = tray.get('cls')(app=self)
             # store a copy of the tray name in the instance so it can be accessed by the
             # plugin itself
             tray_item_label = tray.get('label')

jdaviz/core/template_mixin.py

@@ -52,6 +52,7 @@
 from jdaviz.core.region_translators import regions2roi, _get_region_from_spatial_subset
 from jdaviz.core.tools import ICON_DIR
 from jdaviz.core.user_api import UserApiWrapper, PluginUserApi
+from jdaviz.core.registries import tray_registry
 from jdaviz.style_registry import PopoutStyleWrapper
 from jdaviz.utils import get_subset_type, is_wcs_only, is_not_wcs_only, _wcs_only_label
 
@@ -199,6 +200,9 @@ def __init__(self, *args, **kwargs):
         self.hub.subscribe(self, ViewerRemovedMessage,
                            handler=lambda msg: self._remove_viewer_callbacks(msg.viewer_id))
 
+    def new(self):
+        return self.__class__(app=self.app)
+
     @property
     def app(self):
         """
@@ -356,7 +360,7 @@ class PluginTemplateMixin(TemplateMixin):
     previews_temp_disabled = Bool(False).tag(sync=True)  # noqa use along-side @with_temp_disable() and <plugin-previews-temp-disabled :previews_temp_disabled.sync="previews_temp_disabled" :previews_last_time="previews_last_time" :show_live_preview.sync="show_live_preview"/>
     previews_last_time = Float(0).tag(sync=True)
 
-    def __init__(self, **kwargs):
+    def __init__(self, app, **kwargs):
         self._viewer_callbacks = {}
         # _inactive_thread: thread checking for alive pings to control plugin_opened
         self._inactive_thread = None
@@ -372,7 +376,27 @@ def __init__(self, **kwargs):
         # in repeated toggling of is_active.  To use, decorate any method that observes traitlet
         # changes (including is_active) with @skip_if_no_updates_since_last_active()
         self._methods_skip_since_last_active = []
-        super().__init__(**kwargs)
+
+        # get default viewer names from the helper, according to the requirements of the plugin
+        for registry_name, tray_item in tray_registry.members.items():
+            if tray_item['cls'] == self.__class__:
+                # If viewer reference names need to be passed to the tray item
+                # constructor, pass the names into the constructor in the format
+                # that the tray items expect.
+                tray_registry_options = tray_item.get('viewer_reference_name_kwargs', {})
+                for opt_attr, [opt_kwarg, get_name_kwargs] in tray_registry_options.items():
+                    opt_value = getattr(
+                        self, opt_attr, app._get_first_viewer_reference_name(**get_name_kwargs)
+                    )
+
+                    if opt_value is None:
+                        continue
+
+                    kwargs.setdefault(opt_kwarg, opt_value)
+
+                break
+
+        super().__init__(app=app, **kwargs)
 
     @property
     def user_api(self):