WIP: Add an ij.py.show_ui function

It takes care to show the UI on the AWT event dispatch thread.

If the UI is already visible, it raises the application frame instead of
calling ij.ui().showUI() again, since SciJava Common currently has a bug
when doing that where it hoses the UI (see scijava/scijava-common#460).

Author: ctrueden

src/imagej/__init__.py

@@ -391,6 +391,25 @@ def show(self, image, cmap=None):
         pyplot.imshow(self.from_java(image), interpolation="nearest", cmap=cmap)
         pyplot.show()
 
+    def show_ui(self, name: str = None) -> None:
+        """Display the ImageJ2 user interface.
+
+        :param name: The name of the ImageJ2 UI to show, or None for the
+                     default interface, which is "legacy" (the original ImageJ
+                     UI) when the add_legacy initialization flag is set, and
+                     "swing" (the "pure ImageJ2" UI) otherwise.
+        """
+
+        ij = self._ij
+        def show_or_raise_ui():
+            ui = ij.ui().getDefaultUI() if name is None else ij.ui().getUI(name)
+            if ui.isVisible():
+                ui.getApplicationFrame().setVisible(True)
+            else:
+                ui.show()
+
+        self._ij.thread().queue(show_or_raise_ui)
+
     def sync_image(self, imp: "jc.ImagePlus" = None):
         """Synchronize data between ImageJ and ImageJ2.