This widget can only have one child. To lay out multiple children, let this
widget's child be a widget such as Row, Column, or Stack, which have a
children property, and then provide the children to that widget.A key that is only equal to itself.
Creates a key that is equal only to itself.
The hash code for this object. [...]
A representation of the runtime type of the object.
Returns a string representation of this object.
Invoked when a non-existent method or property is accessed. [...]