measure
Measures the retained tree under constraints.
An empty tree returns IntSize.Zero. A clean node with equal constraints may reuse its retained size and skip its measure callback. Measurement invalidation reruns local measurement and marks local layout, paint, and semantics work dirty. It propagates measurement work to ancestors without dirtying descendants directly. A callback or scope exception poisons the tree after pipeline work begins only when it escapes the owning callback.
Return
the measured root size, or IntSize.Zero when no root is installed.
Parameters
the root constraints.
Throws
when a measure callback or scope operation fails after pipeline work begins. The original throwable is propagated unchanged after cleanup attempts.
when the operation is called from another execution owner. It is also thrown when the operation re-enters an active operation or the tree is not active.