signals

src/textual/dom.py

@@ -1505,7 +1505,7 @@ class DOMNode(MessagePump):
         See [actions](/guide/actions#dynamic-actions) for how to use this method.
 
         """
-        self.call_later(self.screen.refresh_bindings)
+        self.screen.refresh_bindings()
 
     async def action_toggle(self, attribute_name: str) -> None:
         """Toggle an attribute on the node.

src/textual/message_pump.py

@@ -245,7 +245,7 @@ class MessagePump(metaclass=_MessagePumpMeta):
             return node
 
     @property
-    def _is_linked_to_app(self) -> bool:
+    def is_attached(self) -> bool:
         """Is this node linked to the app through the DOM?"""
         node: MessagePump | None = self
 
@@ -275,19 +275,6 @@ class MessagePump(metaclass=_MessagePumpMeta):
         """
         return self.app._logger
 
-    @property
-    def is_attached(self) -> bool:
-        """Is the node attached to the app via the DOM?"""
-        from .app import App
-
-        node = self
-
-        while not isinstance(node, App):
-            if node._parent is None:
-                return False
-            node = node._parent
-        return True
-
     def _attach(self, parent: MessagePump) -> None:
         """Set the parent, and therefore attach this node to the tree.
 

src/textual/signal.py

@@ -52,7 +52,12 @@ class Signal(Generic[SignalT]):
         yield "name", self._name
         yield "subscriptions", list(self._subscriptions.keys())
 
-    def subscribe(self, node: MessagePump, callback: SignalCallbackType) -> None:
+    def subscribe(
+        self,
+        node: MessagePump,
+        callback: SignalCallbackType,
+        immediate: bool = False,
+    ) -> None:
         """Subscribe a node to this signal.
 
         When the signal is published, the callback will be invoked.
@@ -60,17 +65,29 @@ class Signal(Generic[SignalT]):
         Args:
             node: Node to subscribe.
             callback: A callback function which takes a single argument and returns anything (return type ignored).
+            immediate: Invoke the callback immediately on publish if `True`, otherwise post it to the DOM node.
 
         Raises:
             SignalError: Raised when subscribing a non-mounted widget.
         """
+        if immediate:
+
+            def signal_callback(data: object):
+                """Invoke the callback immediately."""
+                callback(data)
+
+        else:
+
+            def signal_callback(data: object):
+                """Post the callback to the node, to call at the next opertunity."""
+                node.call_next(callback, data)
+
         if not node.is_running:
             raise SignalError(
                 f"Node must be running to subscribe to a signal (has {node} been mounted)?"
             )
         callbacks = self._subscriptions.setdefault(node, [])
-        if callback not in callbacks:
-            callbacks.append(callback)
+        callbacks.append(signal_callback)
 
     def unsubscribe(self, node: MessagePump) -> None:
         """Unsubscribe a node from this signal.

src/textual/widget.py

@@ -934,7 +934,7 @@ class Widget(DOMNode):
             Only one of ``before`` or ``after`` can be provided. If both are
             provided a ``MountError`` will be raised.
         """
-        if not self._is_linked_to_app:
+        if not self.is_attached:
             raise MountError(f"Can't mount widget(s) before {self!r} is mounted")
         # Check for duplicate IDs in the incoming widgets
         ids_to_mount = [widget.id for widget in widgets if widget.id is not None]
@@ -1126,7 +1126,7 @@ class Widget(DOMNode):
         if self._parent is not None:
             async with self.batch():
                 await self.query("*").exclude(".-textual-system").remove()
-                if self._is_linked_to_app:
+                if self.is_attached:
                     await self.mount_all(compose(self))
 
     def _post_register(self, app: App) -> None:

tests/test_suspend.py

@@ -48,8 +48,8 @@ async def test_suspend_supported(capfd: pytest.CaptureFixture[str]) -> None:
             calls.add("resume signal")
 
         def on_mount(self) -> None:
-            self.app_suspend_signal.subscribe(self, self.on_suspend)
-            self.app_resume_signal.subscribe(self, self.on_resume)
+            self.app_suspend_signal.subscribe(self, self.on_suspend, immediate=True)
+            self.app_resume_signal.subscribe(self, self.on_resume, immediate=True)
 
     async with SuspendApp(driver_class=HeadlessSuspendDriver).run_test(
         headless=False