Question about Tree.select_node()

[liancheng]

I was building an app displaying a tree of Tmux sessions, windows, and panes, with panes as leaf nodes. One of the panes is special and I want the leaf node representing that pane selected when the tree is initially displayed. However, select_node() did not deliver the effect I needed.

I tried to build a minimal reproduction to illustrate what works and what does not.

The following code works well. Leaf node n0 gets selected:

from textual.app import App, ComposeResult
from textual.widgets import Tree


class TreeNodeSelection(App):
    def compose(self) -> ComposeResult:
        tree = Tree[None]("Root")
        self.n0 = tree.root.add_leaf("n0")
        tree.root.expand_all()
        yield tree

    def on_mount(self):
        tree = self.query_one(Tree[None])
        tree.select_node(self.n0)


TreeNodeSelection().run()

This one, however, does not get n0 selected:

from textual.app import App, ComposeResult
from textual.widgets import Tree


class TreeNodeSelection(App):
    def compose(self) -> ComposeResult:
        tree = Tree[None]("Root")
        yield tree

    def on_mount(self):
        tree = self.query_one(Tree[None])
        self.n0 = tree.root.add_leaf("n0")
        tree.root.expand_all()
        tree.select_node(self.n0)


TreeNodeSelection().run()

Further debugging showed that in the 2nd example, self.n0.line is -1 before select_node() but becomes 1 after select_node(), and adding another select_node() call properly selects n0:

    def on_mount(self):
        tree = self.query_one(Tree[None])
        self.n0 = tree.root.add_leaf("n0")
        tree.root.expand_all()
        self.log(f"Before 1st selectoin: n0.line = {self.n0.line}")
        tree.select_node(self.n0)
        self.log(f"After 1st selectoin: n0.line = {self.n0.line}")
        tree.select_node(self.n0)

Logs:

[21:20:57] INFO                                                 tree_node_selection.py:15
Before 1st selectoin: n0.line = -1
[21:20:57] INFO                                                 tree_node_selection.py:17
After 1st selectoin: n0.line = 1

Is this expected? Do I need some sort of refreshing/redrawing in order to achieve what I need?