Easier customization of Header title

CHANGELOG.md

@@ -20,6 +20,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - Added `OptionList.set_options` https://github.com/Textualize/textual/pull/6048
 - Added `TextArea.suggestion` https://github.com/Textualize/textual/pull/6048
 - Added `TextArea.placeholder` https://github.com/Textualize/textual/pull/6048
+- Added `Header.format_title` and `App.format_title` for easier customization of title in the Header
 
 ### Changed
 

src/textual/app.py

@@ -94,6 +94,7 @@ from textual.await_remove import AwaitRemove
 from textual.binding import Binding, BindingsMap, BindingType, Keymap
 from textual.command import CommandListItem, CommandPalette, Provider, SimpleProvider
 from textual.compose import compose
+from textual.content import Content
 from textual.css.errors import StylesheetError
 from textual.css.query import NoMatches
 from textual.css.stylesheet import RulesMap, Stylesheet
@@ -963,6 +964,23 @@ class App(Generic[ReturnType], DOMNode):
         """
         return self._clipboard
 
+    def format_title(self, title: str, sub_title: str) -> Content:
+        """Format the title for display.
+
+        Args:
+            title: The title.
+            sub_title: The sub title.
+
+        Returns:
+            Content instance with title and subtitle.
+        """
+        title_content = Content(title)
+        sub_title_content = Content(sub_title)
+        if sub_title_content:
+            return Content.assemble(title_content, " — ", sub_title_content)
+        else:
+            return title_content
+
     @contextmanager
     def batch_update(self) -> Generator[None, None, None]:
         """A context manager to suspend all repaints until the end of the batch."""

src/textual/widgets/_header.py

@@ -7,10 +7,12 @@ from datetime import datetime
 from rich.text import Text
 
 from textual.app import RenderResult
+from textual.content import Content
 from textual.dom import NoScreen
 from textual.events import Click, Mount
 from textual.reactive import Reactive
 from textual.widget import Widget
+from textual.widgets import Static
 
 
 class HeaderIcon(Widget):
@@ -98,34 +100,18 @@ class HeaderClock(HeaderClockSpace):
         return Text(datetime.now().time().strftime(self.time_format))
 
 
-class HeaderTitle(Widget):
+class HeaderTitle(Static):
     """Display the title / subtitle in the header."""
 
     DEFAULT_CSS = """
     HeaderTitle {
+        text-wrap: nowrap;
+        text-overflow: ellipsis;
         content-align: center middle;
         width: 100%;
     }
     """
 
-    text: Reactive[str] = Reactive("")
-    """The main title text."""
-
-    sub_text = Reactive("")
-    """The sub-title text."""
-
-    def render(self) -> RenderResult:
-        """Render the title and sub-title.
-
-        Returns:
-            The value to render.
-        """
-        text = Text(self.text, no_wrap=True, overflow="ellipsis")
-        if self.sub_text:
-            text.append(" — ")
-            text.append(self.sub_text, "dim")
-        return text
-
 
 class Header(Widget):
     """A header widget with icon and clock."""
@@ -196,6 +182,17 @@ class Header(Widget):
     def _on_click(self):
         self.toggle_class("-tall")
 
+    def format_title(self) -> Content:
+        """Format the title and subtitle.
+
+        Defers to [App.format_title][textual.app.App.format_title] by default.
+        Override this method if you want to customize how the title is displayed in the header.
+
+        Returns:
+            Content for title display.
+        """
+        return self.app.format_title(self.screen_title, self.screen_sub_title)
+
     @property
     def screen_title(self) -> str:
         """The title that this header will display.
@@ -221,17 +218,11 @@ class Header(Widget):
     def _on_mount(self, _: Mount) -> None:
         async def set_title() -> None:
             try:
-                self.query_one(HeaderTitle).text = self.screen_title
-            except NoScreen:
-                pass
-
-        async def set_sub_title() -> None:
-            try:
-                self.query_one(HeaderTitle).sub_text = self.screen_sub_title
+                self.query_one(HeaderTitle).update(self.format_title())
             except NoScreen:
                 pass
 
         self.watch(self.app, "title", set_title)
-        self.watch(self.app, "sub_title", set_sub_title)
+        self.watch(self.app, "sub_title", set_title)
         self.watch(self.screen, "title", set_title)
-        self.watch(self.screen, "sub_title", set_sub_title)
+        self.watch(self.screen, "sub_title", set_title)

tests/snapshot_tests/snapshot_apps/fr_with_min.py

@@ -25,7 +25,7 @@ class ScreenSplitApp(App[None]):
         background: $panel;
     }
 
-    Static {
+    #scroll1 Static, #scroll2 Static {
         width: 1fr;
         content-align: center middle;
         background: $boost;

tests/test_header.py

@@ -1,6 +1,6 @@
 from textual.app import App
 from textual.screen import Screen
-from textual.widgets import Header
+from textual.widgets import Header, Static
 
 
 async def test_screen_title_none_is_ignored():
@@ -16,7 +16,7 @@ async def test_screen_title_none_is_ignored():
 
     app = MyApp()
     async with app.run_test():
-        assert app.screen.query_one("HeaderTitle").text == "app title"
+        assert app.screen.query_one("HeaderTitle", Static).content == "app title"
 
 
 async def test_screen_title_overrides_app_title():
@@ -34,7 +34,7 @@ async def test_screen_title_overrides_app_title():
 
     app = MyApp()
     async with app.run_test():
-        assert app.screen.query_one("HeaderTitle").text == "screen title"
+        assert app.screen.query_one("HeaderTitle", Static).content == "screen title"
 
 
 async def test_screen_title_reactive_updates_title():
@@ -54,7 +54,7 @@ async def test_screen_title_reactive_updates_title():
     async with app.run_test() as pilot:
         app.screen.title = "new screen title"
         await pilot.pause()
-        assert app.screen.query_one("HeaderTitle").text == "new screen title"
+        assert app.screen.query_one("HeaderTitle", Static).content == "new screen title"
 
 
 async def test_app_title_reactive_does_not_update_title_when_screen_title_is_set():
@@ -74,7 +74,7 @@ async def test_app_title_reactive_does_not_update_title_when_screen_title_is_set
     async with app.run_test() as pilot:
         app.title = "new app title"
         await pilot.pause()
-        assert app.screen.query_one("HeaderTitle").text == "screen title"
+        assert app.screen.query_one("HeaderTitle", Static).content == "screen title"
 
 
 async def test_screen_sub_title_none_is_ignored():
@@ -90,7 +90,10 @@ async def test_screen_sub_title_none_is_ignored():
 
     app = MyApp()
     async with app.run_test():
-        assert app.screen.query_one("HeaderTitle").sub_text == "app sub-title"
+        assert (
+            app.screen.query_one("HeaderTitle", Static).content
+            == "MyApp — app sub-title"
+        )
 
 
 async def test_screen_sub_title_overrides_app_sub_title():
@@ -108,7 +111,10 @@ async def test_screen_sub_title_overrides_app_sub_title():
 
     app = MyApp()
     async with app.run_test():
-        assert app.screen.query_one("HeaderTitle").sub_text == "screen sub-title"
+        assert (
+            app.screen.query_one("HeaderTitle", Static).content
+            == "MyApp — screen sub-title"
+        )
 
 
 async def test_screen_sub_title_reactive_updates_sub_title():
@@ -128,24 +134,7 @@ async def test_screen_sub_title_reactive_updates_sub_title():
     async with app.run_test() as pilot:
         app.screen.sub_title = "new screen sub-title"
         await pilot.pause()
-        assert app.screen.query_one("HeaderTitle").sub_text == "new screen sub-title"
-
-
-async def test_app_sub_title_reactive_does_not_update_sub_title_when_screen_sub_title_is_set():
-    class MyScreen(Screen):
-        SUB_TITLE = "screen sub-title"
-
-        def compose(self):
-            yield Header()
-
-    class MyApp(App):
-        SUB_TITLE = "app sub-title"
-
-        def on_mount(self):
-            self.push_screen(MyScreen())
-
-    app = MyApp()
-    async with app.run_test() as pilot:
-        app.sub_title = "new app sub-title"
-        await pilot.pause()
-        assert app.screen.query_one("HeaderTitle").sub_text == "screen sub-title"
+        assert (
+            app.screen.query_one("HeaderTitle", Static).content
+            == "MyApp — new screen sub-title"
+        )