Tabbed content activated message (#2260)

* Add a message for the tabbed content activated

* Add a docstring

* Testing tabbed content activated message

* Update changelog

* Add reference to the docs about TabbedContent.TabActivated

CHANGELOG.md

@@ -11,6 +11,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 - Added `DataTable.remove_row` method https://github.com/Textualize/textual/pull/2253
 - `Widget.scroll_to_center` now scrolls the widget to the center of the screen https://github.com/Textualize/textual/pull/2255
+- Added `TabActivated` message to `TabbedContent` https://github.com/Textualize/textual/pull/2260
 
 ## [0.19.1] - 2023-04-10
 

docs/widgets/tabbed_content.md

@@ -101,6 +101,10 @@ The following example contains a `TabbedContent` with three tabs.
 | `active` | `str` | `""`    | The `id` attribute of the active tab. Set this to switch tabs. |
 
 
+## Messages
+
+- [TabbedContent.TabActivated][textual.widgets.TabbedContent.TabActivated]
+
 ## See also
 
 

docs/widgets/tabs.md

@@ -61,7 +61,7 @@ The following example adds a `Tabs` widget above a text label. Press ++a++ to ad
 
 ## Messages
 
-- [Tabs.TabActivate][textual.widgets.Tabs.TabActivated]
+- [Tabs.TabActivated][textual.widgets.Tabs.TabActivated]
 - [Tabs.Cleared][textual.widgets.Tabs.Cleared]
 
 ## Bindings

src/textual/widgets/_tabbed_content.py

@@ -2,9 +2,11 @@ from __future__ import annotations
 
 from itertools import zip_longest
 
+from rich.repr import Result
 from rich.text import Text, TextType
 
 from ..app import ComposeResult
+from ..message import Message
 from ..reactive import reactive
 from ..widget import Widget
 from ._content_switcher import ContentSwitcher
@@ -84,6 +86,24 @@ class TabbedContent(Widget):
     active: reactive[str] = reactive("", init=False)
     """The ID of the active tab, or empty string if none are active."""
 
+    class TabActivated(Message):
+        """Posted when the active tab changes."""
+
+        def __init__(self, tabbed_content: TabbedContent, tab: Tab) -> None:
+            """Initialize message.
+
+            Args:
+                tabbed_content: The TabbedContent widget.
+                tab: The Tab widget that was selected (contains the tab label).
+            """
+            self.tabbed_content = tabbed_content
+            self.tab = tab
+            super().__init__()
+
+        def __rich_repr__(self) -> Result:
+            yield self.tabbed_content
+            yield self.tab
+
     def __init__(self, *titles: TextType, initial: str = "") -> None:
         """Initialize a TabbedContent widgets.
 
@@ -167,6 +187,12 @@ class TabbedContent(Widget):
         assert isinstance(event.tab, ContentTab)
         switcher.current = event.tab.id
         self.active = event.tab.id
+        self.post_message(
+            TabbedContent.TabActivated(
+                tabbed_content=self,
+                tab=event.tab,
+            )
+        )
 
     def _on_tabs_cleared(self, event: Tabs.Cleared) -> None:
         """All tabs were removed."""

tests/test_tabbed_content.py

@@ -14,7 +14,7 @@ async def test_tabbed_content_switch():
                     yield Label("Foo", id="foo-label")
                 with TabPane("bar", id="bar"):
                     yield Label("Bar", id="bar-label")
-                with TabPane("baz`", id="baz"):
+                with TabPane("baz", id="baz"):
                     yield Label("Baz", id="baz-label")
 
     app = TabbedApp()
@@ -73,11 +73,11 @@ async def test_tabbed_content_initial():
                     yield Label("Foo", id="foo-label")
                 with TabPane("bar", id="bar"):
                     yield Label("Bar", id="bar-label")
-                with TabPane("baz`", id="baz"):
+                with TabPane("baz", id="baz"):
                     yield Label("Baz", id="baz-label")
 
     app = TabbedApp()
-    async with app.run_test() as pilot:
+    async with app.run_test():
         tabbed_content = app.query_one(TabbedContent)
         assert tabbed_content.active == "bar"
 
@@ -85,3 +85,31 @@ async def test_tabbed_content_initial():
         assert not app.query_one("#foo-label").region
         assert app.query_one("#bar-label").region
         assert not app.query_one("#baz-label").region
+
+
+async def test_tabbed_content_messages():
+    class TabbedApp(App):
+        message = None
+
+        def compose(self) -> ComposeResult:
+            with TabbedContent(initial="bar"):
+                with TabPane("foo", id="foo"):
+                    yield Label("Foo", id="foo-label")
+
+                with TabPane("bar", id="bar"):
+                    yield Label("Bar", id="bar-label")
+                with TabPane("baz", id="baz"):
+                    yield Label("Baz", id="baz-label")
+
+        def on_tabbed_content_tab_activated(
+            self, event: TabbedContent.TabActivated
+        ) -> None:
+            self.message = event
+
+    app = TabbedApp()
+    async with app.run_test() as pilot:
+        tabbed_content = app.query_one(TabbedContent)
+        tabbed_content.active = "bar"
+        await pilot.pause()
+        assert isinstance(app.message, TabbedContent.TabActivated)
+        assert app.message.tab.label.plain == "bar"