Problem Statement
How does InheritedWidget work internally? Explain how it efficiently propagates data and rebuilds dependent widgets.
Explanation
InheritedWidget maintains a registry of all widgets that depend on it using context.dependOnInheritedWidgetOfExactType(). When a descendant calls this method, Flutter records the dependency, establishing a connection between the InheritedWidget and the dependent widget. When the InheritedWidget is replaced (parent rebuilds with new InheritedWidget instance), Flutter checks if the data changed using the updateShouldNotify() method.
If updateShouldNotify() returns true, Flutter notifies all registered dependent widgets, marking them dirty and scheduling rebuilds. Only widgets that explicitly called dependOnInheritedWidgetOfExactType() rebuild - intermediate widgets and non-dependent widgets don't rebuild even though the InheritedWidget changed. This selective rebuilding is what makes InheritedWidget efficient for propagating data through large widget trees.
The updateShouldNotify() method is crucial for performance - it receives the old widget and returns bool indicating whether dependents should rebuild. Implement it to compare old and new data, returning true only when meaningful changes occurred. For example, compare data properties with != to determine if notification is necessary. Returning true when data hasn't actually changed wastes resources rebuilding widgets unnecessarily.
InheritedWidget doesn't store state itself - it's immutable like all widgets. To make data mutable, combine InheritedWidget with StatefulWidget: the State object holds mutable data, and InheritedWidget propagates it. This is the pattern Provider and other solutions use internally. Understanding InheritedWidget's mechanics helps you use state management solutions effectively and debug issues when widgets don't rebuild as expected.