For similar reasons, the RenderSliverBoxChildManager interface has a new getter, childCount, which must return a non-null value if createChild can return null. In practice, it is unusual to implement this interface, so this should have no effect. It is more common to implement the widgets-layer equivalent, SliverChildDelegate. This interface already had an estimatedChildCount getter. The getter continues to exist, though its semantics have been adjusted a little to require that the returned value be accurate if the build method on the delegate ever returns null.

v0.0.21

#13734, #14055, and #14177 substantially revised the InputDecorator et al. widgets. The layout of the input decorator’s parts has changed a little, which means that the internal layout of text fields has changed as well. Tests that depend on the internal geometry of text fields will need to be updated.