SpanSizeLookup

SpanSizeLookup is a component of Android’s RecyclerView library that allows developers to customize the number of span columns that an item occupies in a grid layout managed by GridLayoutManager. It is an abstract inner class of GridLayoutManager, and by overriding its abstract method getSpanSize(int position) you can specify the span size for each item based on its adapter position.

When a RecyclerView is configured with a GridLayoutManager, each item is placed in a grid of columns defined by the spanCount parameter. By default every item occupies one column. The SpanSizeLookup mechanism permits items to span multiple columns or even to fill the entire row, enabling heterogeneous grid designs such as headers, footers, or featured content blocks. The method is called during layout to determine how many of the available columns a particular adapter item should occupy, and the layout manager adjusts item placement accordingly.

Typical use cases include creating lists that contain large banner items that span all columns, or items that occupy half the width in a two-column grid. Developers can also use the SpanSizeLookup to create waterfall or masonry‑style layouts by varying span sizes programmatically based on data attributes.

The SpanSizeLookup is not part of the data set itself; it is purely a layout helper. It can be set via GridLayoutManager.setSpanSizeLookup(SpanSizeLookup) and updated dynamically. Because the method may be invoked frequently during scrolling, it should execute efficiently. The lookup can also cache results if performance becomes an issue. Proper handling of span changes during adapter updates ensures the RecyclerView re–measures items when necessary. This feature provides a flexible way to build richly designed grid interfaces without resorting to custom layout managers.