Tree

ui.Tree creates a tree whose items ui.TreeItem builds, each inside the item it belongs to. An item's children show while its *bool is true; a click on its arrow opens or closes it, and Clicked reports a click elsewhere on it, or Enter, for choosing it, which Selected shows.

item := func(path, label string, open *bool, children func()) {
	if ui.TreeItem(c, label, open, children).Selected(app.chosen == path).Clicked() {
		app.chosen = path
	}
}
ui.Tree(c, func() {
	item("src", "src", &app.srcOpen, func() {
		item("src/main.go", "main.go", nil, nil)
	})
	item("go.mod", "go.mod", nil, nil)
})

Nil children, or a nil open, makes a leaf.

Keyboard

While an item has the keyboard focus, Up and Down move it to the items around, Right opens the item or moves to its first child, and Left closes it or moves to its parent.

A tree builds every item it shows. For trees of thousands of items, or with columns, use an outline, which builds only the rows in view.

Accessibility

Assistive technology sees a tree of items, each with its level, open or closed when it has children.