Fix #2343: Restrict DetailedList title/subtitle to first line

android/src/toga_android/widgets/detailedlist.py

@@ -140,14 +140,10 @@ def _make_row(self, container, i, row):
         row_view.setOnLongClickListener(DetailedListOnLongClickListener(self, i))
         row_height = self.scale_in(64)
 
-        title, subtitle, icon = (
-            getattr(row, attr, None) for attr in self.interface.accessors
-        )
-
         # Add user-provided icon to layout.
         icon_image_view = ImageView(self._native_activity)
-        if icon is not None:
-            icon_image_view.setImageBitmap(icon._impl.native)
+        if self.interface._icon(row) is not None:
+            icon_image_view.setImageBitmap(self.interface._icon(row)._impl.native)
         icon_layout_params = RelativeLayout.LayoutParams(
             RelativeLayout.LayoutParams.WRAP_CONTENT,
             RelativeLayout.LayoutParams.WRAP_CONTENT,
@@ -172,18 +168,14 @@ def _make_row(self, container, i, row):
         text_container.setOrientation(LinearLayout.VERTICAL)
         text_container.setWeightSum(2.0)
 
-        # Create top & bottom text; add them to layout.
-        def get_string(value):
-            if value is None:
-                value = self.interface.missing_value
-            return str(value)
-
+        # _title() and _subtitle() handle None, convert to str, and return only the
+        # first line so that newline characters are not rendered by the TextView.
         top_text = TextView(self._native_activity)
-        top_text.setText(get_string(title))
+        top_text.setText(self.interface._title(row))
         top_text.setTextSize(20.0)
         top_text.setTextColor(self.get_theme_color(R.attr.textColorPrimary))
         bottom_text = TextView(self._native_activity)
-        bottom_text.setText(get_string(subtitle))
+        bottom_text.setText(self.interface._subtitle(row))
         bottom_text.setTextSize(16.0)
         bottom_text.setTextColor(self.get_theme_color(R.attr.textColorSecondary))
         top_text_params = LinearLayout.LayoutParams(

changes/2343.bugfix.md

@@ -0,0 +1 @@
+The `DetailedList` widget now displays only the first line of title and subtitle text.

cocoa/src/toga_cocoa/widgets/detailedlist.py

@@ -86,28 +86,11 @@ def tableView_objectValueForTableColumn_row_(self, table, column, row: int):
             data = TogaData.alloc().init()
             value._impl = data
 
-        try:
-            title = getattr(value, self.interface.accessors[0])
-            if title is not None:
-                title = str(title)
-            else:
-                title = self.interface.missing_value
-        except AttributeError:
-            title = self.interface.missing_value
+        title = self.interface._title(value)
+        subtitle = self.interface._subtitle(value)
 
-        try:
-            subtitle = getattr(value, self.interface.accessors[1])
-            if subtitle is not None:
-                subtitle = str(subtitle)
-            else:
-                subtitle = self.interface.missing_value
-        except AttributeError:
-            subtitle = self.interface.missing_value
-
-        try:
-            icon = getattr(value, self.interface.accessors[2])._impl.native
-        except AttributeError:
-            icon = None
+        icon_obj = self.interface._icon(value)
+        icon = None if icon_obj is None else icon_obj._impl.native
 
         data.attrs = {
             "title": title,

core/src/toga/widgets/detailedlist.py

@@ -186,6 +186,44 @@ def missing_value(self) -> str:
         """
         return self._missing_value
 
+    def _as_text(self, value: object) -> str:
+        """Convert a raw value to a single-line display string (internal helper).
+
+        If the value is None, the widget's missing_value is used instead.
+        Only the first line of the string representation is returned, so
+        that titles and subtitles containing newline characters are not
+        rendered as multiple lines.
+        """
+        if value is None:
+            value = self.missing_value
+        text = str(value)
+        lines = text.splitlines()
+        return lines[0] if lines else ""
+
+    def _title(self, row: object) -> str:
+        """Retrieve the title for a row as a single-line display string.
+
+        Reads the title attribute (first accessor), substitutes missing_value
+        for None, and truncates at the first newline character.
+        """
+        return self._as_text(getattr(row, self._accessors[0], None))
+
+    def _subtitle(self, row: object) -> str:
+        """Retrieve the subtitle for a row as a single-line display string.
+
+        Reads the subtitle attribute (second accessor), substitutes missing_value
+        for None, and truncates at the first newline character.
+        """
+        return self._as_text(getattr(row, self._accessors[1], None))
+
+    def _icon(self, row: object) -> object:
+        """Retrieve the icon for a row.
+
+        Returns the icon object (third accessor), or None if the attribute
+        is absent or not set.
+        """
+        return getattr(row, self._accessors[2], None)
+
     @property
     def selection(self) -> Row | None:
         """The current selection of the table.

core/tests/widgets/test_detailedlist.py

@@ -1,3 +1,4 @@
+from types import SimpleNamespace
 from unittest.mock import Mock
 
 import pytest
@@ -321,3 +322,66 @@ def test_scroll_to_bottom(detailedlist):
     detailedlist.scroll_to_bottom()
 
     assert_action_performed_with(detailedlist, "scroll to row", row=2)
+
+
+@pytest.mark.parametrize(
+    "value, expected",
+    [
+        # Plain text is returned unchanged
+        ("hello", "hello"),
+        # Non-string values are converted to string first
+        (42, "42"),
+        # None is replaced by the widget's missing_value (default is "")
+        (None, ""),
+        # Only the first line is returned when \n is present
+        ("hello\nworld", "hello"),
+        # Windows-style line endings (\r\n) are also handled
+        ("hello\r\nworld", "hello"),
+        # A leading newline means the first line is empty
+        ("\nhello", ""),
+        # A completely empty string stays empty
+        ("", ""),
+    ],
+)
+def test_as_text(detailedlist, value, expected):
+    """_as_text() converts a value to a single-line display string.
+
+    Only the first line of the string representation is returned.
+    None values are replaced by the widget's missing_value.
+    """
+    assert detailedlist._as_text(value) == expected
+
+
+def test_title(detailedlist):
+    """_title() reads the title accessor from a row and returns a single-line string."""
+    # Multiline value is truncated at the first newline
+    row = SimpleNamespace(key="hello\nworld", value="subtitle", icon=None)
+    assert detailedlist._title(row) == "hello"
+
+
+def test_title_missing_attribute(detailedlist):
+    """_title() returns missing_value when the row has no title attribute."""
+    row = SimpleNamespace(value="subtitle", icon=None)  # no 'key' attribute
+    assert detailedlist._title(row) == ""  # default missing_value is ""
+
+
+def test_subtitle(detailedlist):
+    """_subtitle() reads the subtitle attribute from a row as a single-line string."""
+    row = SimpleNamespace(key="title", value="hello\nworld", icon=None)
+    assert detailedlist._subtitle(row) == "hello"
+
+
+def test_subtitle_missing_attribute(detailedlist):
+    """_subtitle() returns missing_value when the row has no subtitle attribute."""
+    row = SimpleNamespace(key="title", icon=None)  # no 'value' attribute
+    assert detailedlist._subtitle(row) == ""  # default missing_value is ""
+
+
+def test_icon(detailedlist):
+    """_icon() returns the icon attribute of a row, or None if absent."""
+    mock_icon = object()
+    row = SimpleNamespace(key="", value="", icon=mock_icon)
+    assert detailedlist._icon(row) is mock_icon
+    assert detailedlist._icon(SimpleNamespace(key="", value="", icon=None)) is None
+    # Missing attribute returns None via getattr default
+    assert detailedlist._icon(SimpleNamespace(key="", value="")) is None

gtk/src/toga_gtk/widgets/detailedlist.py

@@ -56,23 +56,8 @@ def update(self, dl, row):
         and accessors from the detailedList"""
 
         # Set the title and subtitle as a block of HTML text.
-        try:
-            title = getattr(self.row, dl.accessors[0])
-            if title is not None:
-                title = str(title)
-            else:
-                title = dl.missing_value
-        except AttributeError:
-            title = dl.missing_value
-
-        try:
-            subtitle = getattr(self.row, dl.accessors[1])
-            if subtitle is not None:
-                subtitle = str(subtitle)
-            else:
-                subtitle = dl.missing_value
-        except AttributeError:
-            subtitle = dl.missing_value
+        title = dl._title(self.row)
+        subtitle = dl._subtitle(self.row)
 
         markup = "".join(
             [
@@ -89,10 +74,8 @@ def update(self, dl, row):
         if self.icon:
             self.content.remove(self.icon)
 
-        try:
-            pixbuf = getattr(self.row, dl.accessors[2])._impl.native(32)
-        except AttributeError:
-            pixbuf = None
+        icon = dl._icon(self.row)
+        pixbuf = icon._impl.native(32) if icon is not None else None
 
         if pixbuf is not None:
             self.icon = Gtk.Image.new_from_pixbuf(pixbuf)

iOS/src/toga_iOS/widgets/detailedlist.py

@@ -47,30 +47,11 @@ def tableView_cellForRowAtIndexPath_(self, tableView, indexPath):
 
         value = self.interface.data[indexPath.item]
 
-        try:
-            label = getattr(value, self.interface.accessors[0])
-            if label is None:
-                cell.textLabel.text = self.interface.missing_value
-            else:
-                cell.textLabel.text = str(label)
-        except AttributeError:
-            cell.textLabel.text = self.interface.missing_value
-
-        try:
-            label = getattr(value, self.interface.accessors[1])
-            if label is None:
-                cell.detailTextLabel.text = self.interface.missing_value
-            else:
-                cell.detailTextLabel.text = str(label)
-        except AttributeError:
-            cell.detailTextLabel.text = self.interface.missing_value
-
-        try:
-            cell.imageView.image = getattr(
-                value, self.interface.accessors[2]
-            )._impl.native
-        except AttributeError:
-            cell.imageView.image = None
+        cell.textLabel.text = self.interface._title(value)
+        cell.detailTextLabel.text = self.interface._subtitle(value)
+
+        icon = self.interface._icon(value)
+        cell.imageView.image = None if icon is None else icon._impl.native
 
         return cell
 

qt/src/toga_qt/widgets/detailedlist.py

@@ -459,8 +459,15 @@ def create(self):
         self.native_model = ListSourceModel(
             self.interface.data,
             {
-                Qt.ItemDataRole.UserRole: user_formatter,
-                Qt.ItemDataRole.DecorationRole: icon_formatter,
+                Qt.ItemDataRole.UserRole: lambda row, _: (
+                    self.interface._title(row),
+                    self.interface._subtitle(row),
+                ),
+                Qt.ItemDataRole.DecorationRole: lambda row, _: (
+                    icon._impl.native
+                    if (icon := self.interface._icon(row)) is not None
+                    else QIcon()
+                ),
             },
             parent=self.native,
         )

winforms/src/toga_winforms/widgets/detailedlist.py

@@ -746,14 +746,10 @@ def _image_index(self, icon):
 
     def _new_item(self, index) -> tuple[str, str, int]:
         row = self._data[index]
-
-        title, subtitle, icon = (
-            getattr(row, attr, None) for attr in self.interface.accessors
-        )
-
+        icon = self.interface._icon(row)
         return (
-            str(self._missing_value) if title is None else str(title),
-            str(self._missing_value) if subtitle is None else str(subtitle),
+            self.interface._title(row),
+            self.interface._subtitle(row),
             -1 if icon is None else self._image_index(icon._impl),
         )