What is the main purpose of setState () method call?

The State object consists of values that can change. The State object contains its associated widget’s ‘mutable state . ‘ — it stores values that can change over time. When those values have changed, more often than not, the associated StatefulWidget is re-created.

build method Null safety Describes the part of the user interface represented by this widget . The framework calls this method when this widget is inserted into the tree in a given BuildContext and when the dependencies of this widget change (e.g., an InheritedWidget referenced by this widget changes).

Calling setState notifies the framework that the internal state of this object has changed in a way that might impact the user interface in this subtree, which causes the framework to schedule a build for this State object.