Merge pull request #1528 from davep/tree-node-highlighted-message

Add `Tree.NodeHighlighted` message

CHANGELOG.md

@@ -12,6 +12,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - Added `TreeNode.parent` -- a read-only property for accessing a node's parent https://github.com/Textualize/textual/issues/1397
 - Added public `TreeNode` label access via `TreeNode.label` https://github.com/Textualize/textual/issues/1396
 - Added read-only public access to the children of a `TreeNode` via `TreeNode.children` https://github.com/Textualize/textual/issues/1398
+- Added a `Tree.NodeHighlighted` message, giving a `on_tree_node_highlighted` event handler https://github.com/Textualize/textual/issues/1400
 
 ### Changed
 

src/textual/widgets/_tree.py

@@ -330,44 +330,46 @@ class Tree(Generic[TreeDataType], ScrollView, can_focus=True):
         ),
     }
 
-    class NodeSelected(Generic[EventTreeDataType], Message, bubble=True):
+    class NodeMessage(Generic[EventTreeDataType], Message, bubble=True):
+        """Base class for events sent when something happens with a node.
+
+        Attributes:
+            TreeNode[EventTreeDataType]: The node involved in the event.
+        """
+
+        def __init__(
+            self, sender: MessageTarget, node: TreeNode[EventTreeDataType]
+        ) -> None:
+            self.node = node
+            super().__init__(sender)
+
+    class NodeSelected(NodeMessage[EventTreeDataType]):
         """Event sent when a node is selected.
 
         Attributes:
             TreeNode[EventTreeDataType]: The node that was selected.
         """
 
-        def __init__(
-            self, sender: MessageTarget, node: TreeNode[EventTreeDataType]
-        ) -> None:
-            self.node = node
-            super().__init__(sender)
-
-    class NodeExpanded(Generic[EventTreeDataType], Message, bubble=True):
+    class NodeExpanded(NodeMessage[EventTreeDataType]):
         """Event sent when a node is expanded.
 
         Attributes:
             TreeNode[EventTreeDataType]: The node that was expanded.
         """
 
-        def __init__(
-            self, sender: MessageTarget, node: TreeNode[EventTreeDataType]
-        ) -> None:
-            self.node = node
-            super().__init__(sender)
-
-    class NodeCollapsed(Generic[EventTreeDataType], Message, bubble=True):
+    class NodeCollapsed(NodeMessage[EventTreeDataType]):
         """Event sent when a node is collapsed.
 
         Attributes:
             TreeNode[EventTreeDataType]: The node that was collapsed.
         """
 
-        def __init__(
-            self, sender: MessageTarget, node: TreeNode[EventTreeDataType]
-        ) -> None:
-            self.node = node
-            super().__init__(sender)
+    class NodeHighlighted(NodeMessage[EventTreeDataType]):
+        """Event sent when a node is highlighted.
+
+        Attributes:
+            TreeNode[EventTreeDataType]: The node that was collapsed.
+        """
 
     def __init__(
         self,
@@ -577,6 +579,8 @@ class Tree(Generic[TreeDataType], ScrollView, can_focus=True):
             self._refresh_node(node)
             node._selected = True
             self._cursor_node = node
+            if previous_node != node:
+                self.post_message_no_wait(self.NodeHighlighted(self, node))
 
     def watch_guide_depth(self, guide_depth: int) -> None:
         self._invalidate()

tests/tree/test_tree_messages.py

@@ -0,0 +1,78 @@
+from __future__ import annotations
+
+from typing import Any
+from textual.app import App, ComposeResult
+from textual.widgets import Tree
+from textual.message import Message
+
+
+class MyTree(Tree[None]):
+    pass
+
+
+class TreeApp(App[None]):
+    """Test tree app."""
+
+    def __init__(self, *args: Any, **kwargs: Any) -> None:
+        super().__init__(*args, **kwargs)
+        self.messages: list[str] = []
+
+    def compose(self) -> ComposeResult:
+        """Compose the child widgets."""
+        yield MyTree("Root")
+
+    def on_mount(self) -> None:
+        self.query_one(MyTree).root.add("Child")
+        self.query_one(MyTree).focus()
+
+    def record(self, event: Message) -> None:
+        self.messages.append(event.__class__.__name__)
+
+    def on_tree_node_selected(self, event: Tree.NodeSelected[None]) -> None:
+        self.record(event)
+
+    def on_tree_node_expanded(self, event: Tree.NodeExpanded[None]) -> None:
+        self.record(event)
+
+    def on_tree_node_collapsed(self, event: Tree.NodeCollapsed[None]) -> None:
+        self.record(event)
+
+    def on_tree_node_highlighted(self, event: Tree.NodeHighlighted[None]) -> None:
+        self.record(event)
+
+
+async def test_tree_node_selected_message() -> None:
+    """Selecting a node should result in a selected message being emitted."""
+    async with TreeApp().run_test() as pilot:
+        await pilot.press("enter")
+        await pilot.pause(2 / 100)
+        assert pilot.app.messages == ["NodeExpanded", "NodeSelected"]
+
+
+async def test_tree_node_expanded_message() -> None:
+    """Expanding a node should result in an expanded message being emitted."""
+    async with TreeApp().run_test() as pilot:
+        await pilot.press("enter")
+        await pilot.pause(2 / 100)
+        assert pilot.app.messages == ["NodeExpanded", "NodeSelected"]
+
+
+async def test_tree_node_collapsed_message() -> None:
+    """Collapsing a node should result in a collapsed message being emitted."""
+    async with TreeApp().run_test() as pilot:
+        await pilot.press("enter", "enter")
+        await pilot.pause(2 / 100)
+        assert pilot.app.messages == [
+            "NodeExpanded",
+            "NodeSelected",
+            "NodeCollapsed",
+            "NodeSelected",
+        ]
+
+
+async def test_tree_node_highlighted_message() -> None:
+    """Highlighting a node should result in a highlighted message being emitted."""
+    async with TreeApp().run_test() as pilot:
+        await pilot.press("enter", "down")
+        await pilot.pause(2 / 100)
+        assert pilot.app.messages == ["NodeExpanded", "NodeSelected", "NodeHighlighted"]