Remove the ability to create a SplitContainer without content.

changes/1984.removal.3.rst

@@ -0,0 +1 @@
+The ability to create a SplitContainer without content has been removed.

core/src/toga/widgets/splitcontainer.py

@@ -14,7 +14,7 @@ def __init__(
         id=None,
         style=None,
         direction: Direction = Direction.VERTICAL,
-        content: list[Widget | tuple[Widget, int]] | None = None,
+        content: list[Widget | tuple[Widget, int]] = None,
     ):
         """Create a new SplitContainer.
 
@@ -42,8 +42,14 @@ def __init__(
         # Create a platform specific implementation of a SplitContainer
         self._impl = self.factory.SplitContainer(interface=self)
 
-        if content:
-            self.content = content
+        # We can't make content the first argument, but we can't allow it to be empty either.
+        # Raise an error that looks like the one you'd get for missing a required argument.
+        if content is None:
+            raise TypeError(
+                "SplitContainer.__init__() missing 1 required argument: 'content'"
+            )
+
+        self.content = content
         self.direction = direction
 
     @property

core/tests/widgets/test_splitcontainer.py

@@ -38,18 +38,26 @@ def splitcontainer(content1, content2):
     return toga.SplitContainer(content=[content1, content2])
 
 
-def test_widget_created():
-    "A scroll container can be created with no arguments"
-    splitcontainer = toga.SplitContainer()
+def test_create_no_content(app):
+    """SplitContainer can't be created without content."""
+    with pytest.raises(
+        TypeError,
+        match=r"SplitContainer.__init__\(\) missing 1 required argument: 'content'",
+    ):
+        toga.SplitContainer()
+
+
+def test_widget_created(splitcontainer, content1, content2):
+    "A split container can be created with minimal arguments"
     assert splitcontainer._impl.interface == splitcontainer
     assert_action_performed(splitcontainer, "create SplitContainer")
 
-    assert splitcontainer.content == []
+    assert splitcontainer.content == [content1, content2]
     assert splitcontainer.direction == toga.SplitContainer.VERTICAL
 
 
 def test_widget_created_with_values(content1, content2):
-    "A scroll container can be created with arguments"
+    "A split container can be created with arguments"
     splitcontainer = toga.SplitContainer(
         content=[content1, content2],
         direction=toga.SplitContainer.HORIZONTAL,
@@ -68,7 +76,7 @@ def test_widget_created_with_values(content1, content2):
         flex=[1, 1],
     )
 
-    # The scroll container has been refreshed
+    # The split container has been refreshed
     assert_action_performed(splitcontainer, "refresh")
 
 
@@ -77,7 +85,7 @@ def test_assign_to_app(app, splitcontainer, content1, content2):
     # Scroll container is initially unassigned
     assert splitcontainer.app is None
 
-    # Assign the scroll container to the app
+    # Assign the split container to the app
     splitcontainer.app = app
 
     # Scroll container is on the app
@@ -88,26 +96,12 @@ def test_assign_to_app(app, splitcontainer, content1, content2):
     assert content2.app == app
 
 
-def test_assign_to_app_no_content(app):
-    """If the widget is assigned to an app, and there is no content, there's no error"""
-    splitcontainer = toga.SplitContainer()
-
-    # Scroll container is initially unassigned
-    assert splitcontainer.app is None
-
-    # Assign the scroll container to the app
-    splitcontainer.app = app
-
-    # Scroll container is on the app
-    assert splitcontainer.app == app
-
-
 def test_assign_to_window(window, splitcontainer, content1, content2):
     """If the widget is assigned to a window, the content is also assigned"""
     # Scroll container is initially unassigned
     assert splitcontainer.window is None
 
-    # Assign the scroll container to the window
+    # Assign the split container to the window
     splitcontainer.window = window
 
     # Scroll container is on the window
@@ -117,20 +111,6 @@ def test_assign_to_window(window, splitcontainer, content1, content2):
     assert content2.window == window
 
 
-def test_assign_to_window_no_content(window):
-    """If the widget is assigned to an app, and there is no content, there's no error"""
-    splitcontainer = toga.SplitContainer()
-
-    # Scroll container is initially unassigned
-    assert splitcontainer.window is None
-
-    # Assign the scroll container to the window
-    splitcontainer.window = window
-
-    # Scroll container is on the window
-    assert splitcontainer.window == window
-
-
 def test_disable_no_op(splitcontainer):
     "SplitContainer doesn't have a disabled state"
     # Enabled by default
@@ -166,7 +146,7 @@ def test_set_content_widgets(
         flex=[1, 1],
     )
 
-    # The scroll container has been refreshed
+    # The split container has been refreshed
     assert_action_performed(splitcontainer, "refresh")
 
 
@@ -181,7 +161,7 @@ def test_set_content_flex(splitcontainer, content2, content3):
         flex=[2, 3],
     )
 
-    # The scroll container has been refreshed
+    # The split container has been refreshed
     assert_action_performed(splitcontainer, "refresh")
 
 
@@ -196,7 +176,7 @@ def test_set_content_flex_altered(splitcontainer, content2, content3):
         flex=[1, 1],
     )
 
-    # The scroll container has been refreshed
+    # The split container has been refreshed
     assert_action_performed(splitcontainer, "refresh")
 
 
@@ -246,5 +226,5 @@ def test_direction(splitcontainer):
     # The direction has been set
     assert splitcontainer.direction == toga.SplitContainer.HORIZONTAL
 
-    # The scroll container has been refreshed
+    # The split container has been refreshed
     assert_action_performed(splitcontainer, "refresh")

docs/reference/api/containers/splitcontainer.rst

@@ -27,20 +27,27 @@ Usage
 
     split = toga.SplitContainer(content=[left_container, right_container])
 
-Content can be specified when creating the widget, or after creation by assigning
-the ``content`` attribute. The direction of the split can also be configured, either
-at time of creation, or by setting the ``direction`` attribute:
+The content of the SplitContainer must be specified at time of construction. The
+direction of the split can be configured at time of creation, or by setting the
+``direction`` attribute:
 
 .. code-block:: python
 
     import toga
 
-    split = toga.SplitContainer(direction=toga.SplitContainer.HORIZONTAL)
-
     left_container = toga.Box()
     right_container = toga.ScrollContainer()
 
-    split.content = [left_container, right_container]
+    # Make the container a horizontal split initially
+    # (i.e., two panels in a column, with horizontal splitter between them)
+    split = toga.SplitContainer(
+        content=[left_container, right_container],
+        direction=toga.SplitContainer.HORIZONTAL
+    )
+
+    # Make the container a vertical split (i.e., two panels in a row)
+    split.direction = toga.SplitContainer.VERTICAL
+
 
 By default, the content of the SplitContainer will be evenly divided between the
 content. To specify an uneven split, you can provide a flex value when specifying

examples/tutorial2/tutorial/app.py

@@ -57,15 +57,13 @@ def build(app):
 
     right_container.content = right_content
 
-    split = toga.SplitContainer()
-
     # The content of the split container can be specified as a simple list:
     #    split.content = [left_container, right_container]
     # but you can also specify "weight" with each content item, which will
     # set an initial size of the columns to make a "heavy" column wider than
     # a narrower one. In this example, the right container will be twice
     # as wide as the left one.
-    split.content = [(left_container, 1), (right_container, 2)]
+    split = toga.SplitContainer(content=[(left_container, 1), (right_container, 2)])
 
     # Create a "Things" menu group to contain some of the commands.
     # No explicit ordering is provided on the group, so it will appear