automaticDimension

automaticDimension is a sentinel value used in several UI frameworks to indicate that a given dimension should be calculated automatically by the layout engine using Auto Layout constraints rather than specified explicitly by the developer. In Apple's UIKit, the term most commonly appears in relation to table views and, since iOS 10, to collection views.

Table views: To enable dynamic row heights, set the table view's rowHeight to automaticDimension (or UITableView.automaticDimension in Swift). Also provide an estimatedRowHeight to help with initial rendering. The cell's content must be constrained so that its height is determined by its content.

Collection views: Self-sizing cells are supported by configuring the collection view's layout so that item sizes are calculated from content. This is typically achieved by setting the layout's estimatedItemSize to a non-zero value; the system then uses Auto Layout constraints inside each cell to compute its size.

History: In Objective-C, UITableViewAutomaticDimension served the role; Swift uses UITableView.automaticDimension.

Limitations: Works best with well-defined Auto Layout constraints; if constraints are ambiguous or incomplete, heights may be incorrect. It may incur additional computation for large data sets. For improved performance, provide approximate dimensions via estimatedRowHeight or estimatedItemSize.

See also: Auto Layout; Self-sizing cells; UITableViewAutomaticDimension; UITableView.automaticDimension.