key property

Key? key

Controls how one component replaces another component in the tree.

If the runtimeType and key properties of the two components are operator==, respectively, then the new component replaces the old component by updating the underlying element (i.e., by calling Element.update with the new component). Otherwise, the old element is removed from the tree, the new component is inflated into an element, and the new element is inserted into the tree.

In addition, using a GlobalKey as the component's key allows the element to be moved around the tree (changing parent) without losing state. When a new component is found (its key and type do not match a previous component in the same location), but there was a component with that same global key elsewhere in the tree in the previous frame, then that component's element is moved to the new location.

Generally, a component that is the only child of another component does not need an explicit key.

See also:

• The discussions at Key and GlobalKey.

Implementation

final Key? key;