Fix datetime initialization problem (#1762)

* Fix datetime initialization problem

* add regression test for datetime initialization

* update name of test

traitsui/qt4/datetime_editor.py

@@ -38,9 +38,9 @@ def init(self, parent):
         self.maximum_datetime = self.factory.maximum_datetime
 
         self.control = QtGui.QDateTimeEdit()
-        self.control.dateTimeChanged.connect(self.update_object)
         self.update_minimum_datetime()
         self.update_maximum_datetime()
+        self.control.dateTimeChanged.connect(self.update_object)
 
     def dispose(self):
         """Disposes of the contents of an editor."""

traitsui/tests/test_datetime.py

@@ -0,0 +1,71 @@
+# (C) Copyright 2004-2021 Enthought, Inc., Austin, TX
+# All rights reserved.
+#
+# This software is provided without warranty under the terms of the BSD
+# license included in LICENSE.txt and may be redistributed only under
+# the conditions described in the aforementioned license. The license
+# is also available online at http://www.enthought.com/licenses/BSD.txt
+#
+# Thanks for using Enthought open source!
+
+"""
+Test the initialization of a Datetime when given minimum and maximum 
+dates in the DatetimeEditor
+"""
+from datetime import datetime, timedelta
+import unittest
+
+from traits.has_traits import HasTraits
+from traits.trait_types import Datetime
+from traitsui.editors.datetime_editor import DatetimeEditor
+from traitsui.item import Item
+from traitsui.view import View
+
+
+from traitsui.tests._tools import (
+    BaseTestMixin,
+    create_ui,
+    requires_toolkit,
+    reraise_exceptions,
+    ToolkitName,
+)
+
+MAX_DATE = datetime.now()
+MIN_DATE = MAX_DATE - timedelta(days=10)
+DATE = MAX_DATE - timedelta(days=5)
+
+
+class DatetimeInitDailog(HasTraits):
+
+    date = Datetime()
+
+    def _date_default(self):
+        return DATE
+
+    traits_view = View(Item('date', 
+                            editor=DatetimeEditor(
+                                maximum_datetime=MAX_DATE,
+                                minimum_datetime=MIN_DATE)))
+
+
+class TestDatetimeEditor(BaseTestMixin, unittest.TestCase):
+
+    def setUp(self):
+        BaseTestMixin.setUp(self)
+
+    def tearDown(self):
+        BaseTestMixin.tearDown(self)
+
+    @requires_toolkit([ToolkitName.qt])
+    def test_date_initialization(self):
+        # Behavior: for a date initialized between maximum and minimum dates in
+        # DatetimeEditor, that date should be unmodified
+
+        dialog = DatetimeInitDailog()
+
+        # verify that the date is correctly initialized
+        self.assertEqual(dialog.date, DATE)
+
+        with reraise_exceptions(), create_ui(dialog) as ui:
+            # verify that the date hasn't changed after creating the ui
+            self.assertEqual(dialog.date, DATE)