Merge pull request #4392 from Textualize/select-no-changed

prevent messages from constructor

CHANGELOG.md

@@ -5,6 +5,12 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/)
 and this project adheres to [Semantic Versioning](http://semver.org/).
 
+## [0.56.0] - Unreleased
+
+### Changed
+
+- self.prevent can be used in a widget constructor to prevent messages on mount https://github.com/Textualize/textual/pull/4392
+
 ## [0.55.1] - 2024-04-2
 
 ### Fixed

src/textual/message_pump.py

@@ -144,6 +144,7 @@ def __init__(self, parent: MessagePump | None = None) -> None:
         """
         self._next_callbacks: list[events.Callback] = []
         self._thread_id: int = threading.get_ident()
+        self._prevented_messages_on_mount = self._prevent_message_types_stack[-1]
 
     @property
     def _prevent_message_types_stack(self) -> list[set[type[Message]]]:
@@ -524,7 +525,11 @@ async def _pre_process(self) -> bool:
 
         try:
             await self._dispatch_message(events.Compose())
-            await self._dispatch_message(events.Mount())
+            if self._prevented_messages_on_mount:
+                with self.prevent(*self._prevented_messages_on_mount):
+                    await self._dispatch_message(events.Mount())
+            else:
+                await self._dispatch_message(events.Mount())
             self.check_idle()
             self._post_mount()
         except Exception as error:

src/textual/widgets/_select.py

@@ -3,6 +3,7 @@
 from dataclasses import dataclass
 from typing import TYPE_CHECKING, Generic, Iterable, TypeVar, Union
 
+import rich.repr
 from rich.console import RenderableType
 from rich.text import Text
 
@@ -256,6 +257,7 @@ class Select(Generic[SelectType], Vertical, can_focus=True):
     exception.
     """
 
+    @rich.repr.auto
     class Changed(Message):
         """Posted when the select value was changed.
 
@@ -274,6 +276,10 @@ def __init__(
             self.value = value
             """The value of the Select when it changed."""
 
+        def __rich_repr__(self) -> rich.repr.Result:
+            yield self.select
+            yield self.value
+
         @property
         def control(self) -> Select[SelectType]:
             """The Select that sent the message."""