Struct TreeViewHandle 

pub struct TreeViewHandle { /* private fields */ }

A handle on a mounted TreeView, to scroll it to a row from outside the widget — a view-model revealing the node a search found, say.

Rows are addressed by their flat visible index: the position of the row among the rows currently shown, counting the children of expanded nodes and skipping those of collapsed ones (the index the delegate’s selection and the keyboard use).

Cheap to clone, valid before the view is mounted, and it survives the view’s rebuilds. Its methods never compute an offset when they are called: they record the request and ask for a layout pass, and the view applies it there, after row measurement and scroll anchoring have settled. So a structural change made in the same turn (a node expanded above the target, say) is accounted for, a request made before mount is applied at the first layout, and a later request replaces an earlier pending one. A request on an empty tree is dropped; an index past the end reveals the last row.

The handle also reads and moves the tree’s keyboard cursor, the row the arrow keys step from and assistive technology is told is current: cursor, set_cursor and cursor_signal, in the same flat visible indices. In a multiple selection the cursor and the selection are separate: the accelerator with an arrow moves the cursor alone, and a selection written from outside leaves the cursor where it was.

let tree = TreeView::new(model, |item, _entry, _selected| {
    Box::new(TextWidget::new(lit!(item)))
});
let handle = tree.handle();
// … `ctx.add(tree)`; later, after expanding the node's ancestors:
handle.ensure_index_visible(42);

Implementations

impl TreeViewHandle

pub fn scroll_to_index(&self, index: usize)

Scroll so the row at the given flat visible index is aligned to the top of the viewport, as far as the scroll range allows, at the next layout pass.

pub fn ensure_index_visible(&self, index: usize)

Scroll the minimum distance that brings the row at the given flat visible index fully into view, at the next layout pass; no scroll when it already is.

pub fn cursor(&self) -> Option<usize>

The flat visible index the keyboard cursor is on, or None while the tree has no cursor: it has not been navigated, clicked or given one by set_cursor. With no cursor the keys start from the first selected row, and from the first or last row when nothing is selected.

The cursor follows its row: an expansion or a collapse above it, or an insertion, moves the index with the row, and a row that leaves the visible rows takes the cursor with it. In a single selection the cursor follows the selection: the keys move them together, and a selection written from outside moves the cursor onto it. In a multiple selection they are separate: the accelerator with an arrow (Ctrl+Arrow) moves the cursor alone, and a selection written from outside leaves the cursor where it was.

pub fn set_cursor(&self, index: Option<usize>)

Move the keyboard cursor to the row at flat visible index index, or remove it with None.

An index past the last visible row is clamped to that row; on an empty tree the cursor is removed. While the tree holds keyboard focus it names the row as its active descendant at the next accessibility update, when the row is realized; the next arrow key steps from it, and the cursor follows that row through later structural changes.

Keyboard focus and the selection are left alone, and the tree does not scroll: pair it with ensure_index_visible to bring the row into view. Usable before the tree is mounted and across its rebuilds; in a single selection the tree seats the cursor on the selected row when it is built and whenever the selection changes.

pub fn cursor_signal(&self) -> Signal<Option<usize>>

A read-only signal of the cursor, as cursor reports it, for an application to observe or bind: a status line naming the current row, actions enabled for it. It changes with every write of the cursor, by the keys, a click, a structural change moving it or set_cursor.

Trait Implementations

impl Clone for TreeViewHandle

fn clone(&self) -> TreeViewHandle

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for TreeViewHandle

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.