Fix page_up and page_down bug in DataTable when show_header is False (#3093)

CHANGELOG.md

@@ -7,6 +7,8 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 ## Unreleased
 
+- Fixed `page_up` and `page_down` bug in `DataTable` when `show_header = False` https://github.com/Textualize/textual/pull/3093
+
 ### Changed
 
 - grid-columns and grid-rows now accept an `auto` token to detect the optimal size https://github.com/Textualize/textual/pull/3107

src/textual/widgets/_data_table.py

@@ -2205,9 +2205,8 @@ class DataTable(ScrollView, Generic[CellType], can_focus=True):
     def action_page_down(self) -> None:
         """Move the cursor one page down."""
         self._set_hover_cursor(False)
-        cursor_type = self.cursor_type
-        if self.show_cursor and (cursor_type == "cell" or cursor_type == "row"):
-            height = self.size.height - self.header_height if self.show_header else 0
+        if self.show_cursor and self.cursor_type in ("cell", "row"):
+            height = self.size.height - (self.header_height if self.show_header else 0)
 
             # Determine how many rows constitutes a "page"
             offset = 0
@@ -2228,9 +2227,8 @@ class DataTable(ScrollView, Generic[CellType], can_focus=True):
     def action_page_up(self) -> None:
         """Move the cursor one page up."""
         self._set_hover_cursor(False)
-        cursor_type = self.cursor_type
-        if self.show_cursor and (cursor_type == "cell" or cursor_type == "row"):
-            height = self.size.height - self.header_height if self.show_header else 0
+        if self.show_cursor and self.cursor_type in ("cell", "row"):
+            height = self.size.height - (self.header_height if self.show_header else 0)
 
             # Determine how many rows constitutes a "page"
             offset = 0

tests/test_data_table.py

@@ -173,11 +173,13 @@ async def test_empty_table_interactions():
         assert app.message_names == []
 
 
-async def test_cursor_movement_with_home_pagedown_etc():
+@pytest.mark.parametrize("show_header", [True, False])
+async def test_cursor_movement_with_home_pagedown_etc(show_header):
     app = DataTableApp()
 
     async with app.run_test() as pilot:
         table = app.query_one(DataTable)
+        table.show_header = show_header
         table.add_columns("A", "B")
         table.add_rows(ROWS)
         await pilot.press("right", "pagedown")