applyTo method Null safety

  1. @override
FixedExtentScrollPhysics applyTo(
  1. ScrollPhysics? ancestor
)
override

Combines this ScrollPhysics instance with the given physics.

The returned object uses this instance's physics when it has an opinion, and defers to the given ancestor object's physics when it does not.

If parent is null then this returns a ScrollPhysics with the same runtimeType, but where the parent has been replaced with the ancestor.

If this scroll physics object already has a parent, then this method is applied recursively and ancestor will appear at the end of the existing chain of parents.

Calling this method with a null argument will copy the current object. This is inefficient.

link
In the following example, the applyTo method is used to combine the scroll physics of two ScrollPhysics objects. The resulting ScrollPhysics x has the same behavior as y. 
final FooScrollPhysics x = const FooScrollPhysics().applyTo(const BarScrollPhysics());
const FooScrollPhysics y = FooScrollPhysics(parent: BarScrollPhysics());

Implementing applyTo

When creating a custom ScrollPhysics subclass, this method must be implemented. If the physics class has no constructor arguments, then implementing this method is merely a matter of calling the constructor with a parent constructed using buildParent, as follows:

FooScrollPhysics applyTo(ScrollPhysics ancestor) {
  return FooScrollPhysics(parent: buildParent(ancestor));
}

If the physics class has constructor arguments, they must be passed to the constructor here as well, so as to create a clone.

See also:

Implementation

@override
FixedExtentScrollPhysics applyTo(ScrollPhysics? ancestor) {
  return FixedExtentScrollPhysics(parent: buildParent(ancestor));
}