remove flicker (#3757)

* remove flicker

* changelog

CHANGELOG.md

@@ -11,6 +11,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 ### Fixed
 
 - Fixed mouse targeting issue in `TextArea` when tabs were not fully expanded https://github.com/Textualize/textual/pull/3725
+- Fixed flicker when updating Markdown https://github.com/Textualize/textual/pull/3757
 
 ### Added
 

src/textual/screen.py

@@ -645,7 +645,7 @@ def _compositor_refresh(self) -> None:
     def _on_timer_update(self) -> None:
         """Called by the _update_timer."""
         self._update_timer.pause()
-        if self.is_current:
+        if self.is_current and not self.app._batch_count:
             if self._layout_required:
                 self._refresh_layout()
                 self._layout_required = False

src/textual/widgets/_markdown.py

@@ -13,11 +13,12 @@
 
 from .._slug import TrackedSlugs
 from ..app import ComposeResult
+from ..await_complete import AwaitComplete
 from ..containers import Horizontal, Vertical, VerticalScroll
 from ..events import Mount
 from ..message import Message
 from ..reactive import reactive, var
-from ..widget import AwaitMount, Widget
+from ..widget import Widget
 from ..widgets import Static, Tree
 
 TableOfContentsType: TypeAlias = "list[tuple[int, str, str | None]]"
@@ -721,7 +722,7 @@ def unhandled_token(self, token: Token) -> MarkdownBlock | None:
         """
         return None
 
-    def update(self, markdown: str) -> AwaitMount:
+    def update(self, markdown: str) -> AwaitComplete:
         """Update the document with new Markdown.
 
         Args:
@@ -871,9 +872,16 @@ def update(self, markdown: str) -> AwaitMount:
         self.post_message(
             Markdown.TableOfContentsUpdated(self, self._table_of_contents)
         )
-        with self.app.batch_update():
-            self.query("MarkdownBlock").remove()
-            return self.mount_all(output)
+        markdown_block = self.query("MarkdownBlock")
+
+        async def await_update() -> None:
+            """Update in a single batch."""
+
+            with self.app.batch_update():
+                await markdown_block.remove()
+                await self.mount_all(output)
+
+        return AwaitComplete(await_update())
 
 
 class MarkdownTableOfContents(Widget, can_focus_children=True):