LayoutFunction

Positions the children of a container.

Yoga can express a row and a column. It cannot express a pager, where each page sits at a stride the container computes; or a split pane, where a divider the user drags decides the sizes; or a collapsing header, where one child's position depends on another's scroll offset. A layout function is how a container says where its children go.

Children remain part of the parent's Litho tree. They are not a nested tree, so incremental mount, visibility and state all continue to work across them without the container forwarding anything by hand.

Sealed, so the only implementations are the arity shapes below. A container picks one by how many parameters its lambda declares, and the constructor it matches says how many children it may name, so handing a two-child function to a three-child container fails to compile.

The intrinsic-size questions all have answers here, each of which runs the layout function and reads the size back. Override one when the container knows its answer more cheaply — a pager is one page wide however many pages it holds — which needs an object rather than a lambda. An override receives the real children, and an IntrinsicMeasureScope, which cannot measure them.

Inheritors