Updating a TreeNode.label doesn't refresh the tree right away

[davep]

In this little illustration of how a Tree's nodes' labels can be updated on the fly, the actual updates don't show until some other interaction with the Tree takes place (moving the cursor, causing a mouse hover event, etc):

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

class TreeNodeUpdateApp( App[ None ] ):

    BINDINGS = [
        ( "a", "add", "" ),
    ]

    def compose( self ) -> ComposeResult:
        yield Header()
        yield Tree( "100" )
        yield Footer()

    def on_mount( self ) -> None:
        for n in range( 10 ):
            node = self.query_one( Tree ).root.add( str( n ), expand=True )
            for m in range( 10 ):
                node.add_leaf( str( m ) )

    def action_add( self ):
        node = self.query_one( Tree ).cursor_node
        node.label = str( int( str( node.label ) ) + 1 )

if __name__ == "__main__":
    TreeNodeUpdateApp().run()

adding a self.query_one( Tree ).refresh() to the end of action_add fixes it so the update of the label is reflected right away.

TreeNode.set_label should probably be changed to cause the Tree to perform a refresh.

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