Merge pull request #4159 from davep/tabbed-content-active-issue

Fix active tab not coming into view plus `TabbedContent.TabActivated` not always been posted

Author: willmcgugan

CHANGELOG.md

@@ -14,6 +14,11 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - Add undo and redo to TextArea https://github.com/Textualize/textual/pull/4124
 - Added support for command palette command discoverability https://github.com/Textualize/textual/pull/4154
 
+### Fixed
+
+- Fixed out-of-view `Tab` not being scrolled into view when `Tabs.active` is assigned https://github.com/Textualize/textual/issues/4150
+- Fixed `TabbedContent.TabActivate` not being posted when `TabbedContent.active` is assigned https://github.com/Textualize/textual/issues/4150
+
 ### Changed
 
 - Breaking change: Renamed `TextArea.tab_behaviour` to `TextArea.tab_behavior` https://github.com/Textualize/textual/pull/4124

src/textual/widgets/_tabbed_content.py

@@ -511,13 +511,22 @@ def _on_tabs_tab_activated(self, event: Tabs.TabActivated) -> None:
         if self._is_associated_tabs(event.tabs):
             # The message is relevant, so consume it and update state accordingly.
             event.stop()
+            assert event.tab.id is not None
             switcher = self.get_child_by_type(ContentSwitcher)
             switcher.current = ContentTab.sans_prefix(event.tab.id)
-            self.active = ContentTab.sans_prefix(event.tab.id)
+            with self.prevent(self.TabActivated):
+                # We prevent TabbedContent.TabActivated because it is also
+                # posted from the watcher for active, we're also about to
+                # post it below too, which is valid as here we're reacting
+                # to what the Tabs are doing. This ensures we don't get
+                # doubled-up messages.
+                self.active = ContentTab.sans_prefix(event.tab.id)
             self.post_message(
                 TabbedContent.TabActivated(
                     tabbed_content=self,
-                    tab=event.tab,
+                    tab=self.get_child_by_type(ContentTabs).get_content_tab(
+                        self.active
+                    ),
                 )
             )
 
@@ -548,7 +557,14 @@ def _watch_active(self, active: str) -> None:
         """Switch tabs when the active attributes changes."""
         with self.prevent(Tabs.TabActivated):
             self.get_child_by_type(ContentTabs).active = ContentTab.add_prefix(active)
-            self.get_child_by_type(ContentSwitcher).current = active
+        self.get_child_by_type(ContentSwitcher).current = active
+        if active:
+            self.post_message(
+                TabbedContent.TabActivated(
+                    tabbed_content=self,
+                    tab=self.get_child_by_type(ContentTabs).get_content_tab(active),
+                )
+            )
 
     @property
     def tab_count(self) -> int:

src/textual/widgets/_tabs.py

@@ -583,6 +583,7 @@ def watch_active(self, previously_active: str, active: str) -> None:
             self.query("#tabs-list > Tab.-active").remove_class("-active")
             active_tab.add_class("-active")
             self._highlight_active(animate=previously_active != "")
+            self._scroll_active_tab()
             self.post_message(self.TabActivated(self, active_tab))
         else:
             underline = self.query_one(Underline)

tests/test_tabbed_content.py

@@ -1,3 +1,5 @@
+from __future__ import annotations
+
 import pytest
 
 from textual.app import App, ComposeResult
@@ -137,13 +139,12 @@ def compose(self) -> ComposeResult:
 
 async def test_tabbed_content_messages():
     class TabbedApp(App):
-        message = None
+        activation_history: list[Tab] = []
 
         def compose(self) -> ComposeResult:
-            with TabbedContent(initial="bar"):
+            with TabbedContent():
                 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"):
@@ -152,15 +153,19 @@ def compose(self) -> ComposeResult:
         def on_tabbed_content_tab_activated(
             self, event: TabbedContent.TabActivated
         ) -> None:
-            self.message = event
+            self.activation_history.append(event.tab)
 
     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"
+        assert app.activation_history == [
+            # foo was originally activated.
+            app.query_one(TabbedContent).get_tab("foo"),
+            # then we did bar "by hand"
+            app.query_one(TabbedContent).get_tab("bar"),
+        ]
 
 
 async def test_tabbed_content_add_later_from_empty():