Support QMainWindow .ui files in load_ui_file

pydm/display.py

@@ -14,7 +14,9 @@
 
 import re
 import six
-from qtpy.QtWidgets import QApplication, QWidget
+import xml.etree.ElementTree as ET
+
+from qtpy.QtWidgets import QApplication, QMainWindow, QWidget
 
 from .help_files import HelpWindow
 from .utilities import import_module_by_filename, is_pydm_app, macro, ACTIVE_QT_WRAPPER, QtWrapperTypes
@@ -186,6 +188,26 @@ def _load_compiled_ui_into_display(
     display.ui = display
 
 
+def _get_ui_root_widget_class(uifile):
+    """Return the class name of the root widget defined in a .ui file.
+
+    Parameters
+    ----------
+    uifile : str
+        Path to the .ui file.
+
+    Returns
+    -------
+    str
+        The root widget class name (e.g. ``"QWidget"``, ``"QMainWindow"``).
+    """
+    tree = ET.parse(uifile)
+    widget_elem = tree.getroot().find("widget")
+    if widget_elem is not None:
+        return widget_elem.get("class", "QWidget")
+    return "QWidget"
+
+
 def load_ui_file(uifile, macros=None, args=None):
     """
     Load a .ui file, perform macro substitution, then return the resulting QWidget.
@@ -207,7 +229,11 @@ def load_ui_file(uifile, macros=None, args=None):
     QWidget
     """
 
-    display = Display(macros=macros)
+    root_class = _get_ui_root_widget_class(uifile)
+    if root_class == "QMainWindow":
+        display = MainWindowDisplay(macros=macros)
+    else:
+        display = Display(macros=macros)
     display.load_ui_from_file(uifile, macros)
     return display
 
@@ -329,9 +355,26 @@ def load_py_file(pyfile, args=None, macros=None):
 }
 
 
-class Display(QWidget):
-    def __init__(self, parent=None, args=None, macros=None, ui_filename=None):
-        super().__init__(parent)
+class DisplayBase:
+    """Shared implementation for display-like widgets.
+
+    Provides navigation, macro handling, file loading, and stylesheet
+    support.  Mixed into both :class:`Display` (QWidget-based) and
+    :class:`MainWindowDisplay` (QMainWindow-based).
+    """
+
+    def _init_display(self, args=None, macros=None, ui_filename=None):
+        """Initialize display state.  Must be called from subclass ``__init__``.
+
+        Parameters
+        ----------
+        args : list, optional
+            Command-line arguments forwarded to the display.
+        macros : dict, optional
+            Macro substitutions.
+        ui_filename : str, optional
+            Filename of the .ui file to load.
+        """
         self.ui = None
         self.help_window = None
         self._ui_filename = ui_filename
@@ -341,8 +384,6 @@ def __init__(self, parent=None, args=None, macros=None, ui_filename=None):
         self._previous_display = None
         self._next_display = None
         self._local_style = ""
-        if ui_filename or self.ui_filename():
-            self.load_ui(macros=macros)
 
     def loaded_file(self):
         return self._loaded_file
@@ -483,3 +524,32 @@ def setStyleSheet(self, new_stylesheet):
                 self._local_style = f.read()
         logger.debug("Setting stylesheet to: %s", self._local_style)
         super().setStyleSheet(self._local_style)
+
+
+class Display(DisplayBase, QWidget):
+    def __init__(self, parent=None, args=None, macros=None, ui_filename=None):
+        super().__init__(parent)
+        self._init_display(args=args, macros=macros, ui_filename=ui_filename)
+        if ui_filename or self.ui_filename():
+            self.load_ui(macros=macros)
+
+
+class MainWindowDisplay(DisplayBase, QMainWindow):
+    """Display backed by QMainWindow for .ui files that use QMainWindow as
+    their root widget.
+
+    Inherits the full display interface from :class:`DisplayBase` so it
+    passes ``isinstance(widget, Display)`` checks used throughout pydm for
+    navigation, menu items, macro propagation, and help support.
+
+    Parameters
+    ----------
+    parent : QWidget, optional
+        The parent widget.
+    macros : dict, optional
+        Macro substitutions for the display.
+    """
+
+    def __init__(self, parent=None, macros=None):
+        super().__init__(parent)
+        self._init_display(macros=macros)

pydm/main_window.py

@@ -11,7 +11,7 @@
     close_widget_connections,
 )
 from .pydm_ui import Ui_MainWindow
-from .display import Display, ScreenTarget, load_file, clear_compiled_ui_file_cache
+from .display import Display, DisplayBase, ScreenTarget, load_file, clear_compiled_ui_file_cache
 from .connection_inspector import ConnectionInspector
 from .about_pydm import AboutWindow
 from .show_macros import MacroWindow
@@ -255,7 +255,7 @@ def enable_disable_navigation(self):
             self.ui.actionForward.setDisabled(True)
             return
 
-        if not isinstance(w, Display):
+        if not isinstance(w, DisplayBase):
             # We can't do much if it is not a Display and we don't have the
             # previous_display and next_display properties since we don't
             # have the navigation stack set.
@@ -327,7 +327,7 @@ def get_files_in_display(self):
         if extension == ".ui":
             return self.current_file(), None
         else:
-            central_widget = self.centralWidget() if isinstance(self.centralWidget(), Display) else None
+            central_widget = self.centralWidget() if isinstance(self.centralWidget(), DisplayBase) else None
             if central_widget is not None:
                 ui_file = central_widget.ui_filepath()
             return ui_file, self.current_file()
@@ -571,7 +571,7 @@ def show_macro_window(self):
 
     def add_menu_items(self):
         # create the custom menu with user given items
-        if not isinstance(self.display_widget(), Display):
+        if not isinstance(self.display_widget(), DisplayBase):
             return
 
         # Only provide the view help menu option if an associated help file has been loaded

pydm/tests/test_data/mainwindow_test.ui

@@ -0,0 +1,23 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<ui version="4.0">
+ <class>MainWindow</class>
+ <widget class="QMainWindow" name="MainWindow">
+  <property name="geometry">
+   <rect>
+    <x>0</x>
+    <y>0</y>
+    <width>400</width>
+    <height>300</height>
+   </rect>
+  </property>
+  <widget class="QWidget" name="centralwidget">
+   <widget class="QLabel" name="label">
+    <property name="text">
+     <string>Test Label</string>
+    </property>
+   </widget>
+  </widget>
+ </widget>
+ <resources/>
+ <connections/>
+</ui>

pydm/tests/test_mainwindow_display.py

@@ -0,0 +1,67 @@
+import os
+import pytest
+
+from pydm.display import Display, MainWindowDisplay, load_ui_file, _get_ui_root_widget_class
+from qtpy.QtWidgets import QMainWindow, QWidget
+
+TEST_DATA = os.path.join(os.path.dirname(__file__), "test_data")
+MAINWINDOW_UI = os.path.join(TEST_DATA, "mainwindow_test.ui")
+
+
+def test_get_ui_root_widget_class_mainwindow():
+    """Detect QMainWindow as root widget class in a .ui file."""
+    assert _get_ui_root_widget_class(MAINWINDOW_UI) == "QMainWindow"
+
+
+def test_load_mainwindow_ui_returns_mainwindow_display(qtbot):
+    """Loading a QMainWindow .ui file produces a MainWindowDisplay instance.
+
+    Parameters
+    ----------
+    qtbot : fixture
+        pytest-qt fixture for widget management.
+    """
+    display = load_ui_file(MAINWINDOW_UI)
+    qtbot.addWidget(display)
+    assert isinstance(display, MainWindowDisplay)
+    assert isinstance(display, QMainWindow)
+
+
+def test_load_mainwindow_ui_does_not_crash(qtbot):
+    """QMainWindow .ui files should load without AttributeError.
+
+    Parameters
+    ----------
+    qtbot : fixture
+        pytest-qt fixture for widget management.
+    """
+    display = load_ui_file(MAINWINDOW_UI)
+    qtbot.addWidget(display)
+    assert hasattr(display, "setCentralWidget")
+    assert display.centralWidget() is not None
+
+
+def test_mainwindow_display_has_full_display_interface(qtbot):
+    """MainWindowDisplay should have all Display methods so isinstance checks
+    and navigation/menu/macro features work correctly.
+
+    Parameters
+    ----------
+    qtbot : fixture
+        pytest-qt fixture for widget management.
+    """
+    display = load_ui_file(MAINWINDOW_UI)
+    qtbot.addWidget(display)
+
+    assert hasattr(display, "args")
+    assert hasattr(display, "macros")
+    assert hasattr(display, "loaded_file")
+    assert hasattr(display, "menu_items")
+    assert hasattr(display, "file_menu_items")
+    assert hasattr(display, "show_help")
+    assert hasattr(display, "navigate_back")
+    assert hasattr(display, "navigate_forward")
+    assert hasattr(display, "load_ui_from_file")
+    assert hasattr(display, "load_help_file")
+    assert hasattr(display, "previous_display")
+    assert hasattr(display, "next_display")

pydm/widgets/base.py

@@ -14,7 +14,7 @@
 from .channel import PyDMChannel
 from pydm import data_plugins, tools, config
 from pydm.utilities import is_qt_designer, remove_protocol
-from pydm.display import Display
+from pydm.display import Display, DisplayBase
 from pydm.utilities import ACTIVE_QT_WRAPPER, QtWrapperTypes
 
 if ACTIVE_QT_WRAPPER == QtWrapperTypes.PYSIDE6:
@@ -368,7 +368,7 @@ def setRules(self, new_rules) -> None:
     def find_parent_display(self):
         widget = self.parent()
         while widget is not None:
-            if isinstance(widget, Display):
+            if isinstance(widget, DisplayBase):
                 return widget
             widget = widget.parent()
         return None