Problem Statement
What does the 'mounted' property indicate in a State object?
Explanation
The mounted property is true when the State object is currently in the widget tree and false after dispose() is called. It's crucial for checking before calling setState() in asynchronous callbacks to prevent errors when the widget has been removed from the tree while an async operation was in progress.
Common pattern: After an async operation like a network request, check if (mounted) before calling setState() to avoid calling it on a disposed State object, which throws an error. Without this check, long-running async operations might complete after the user navigates away, trying to update a widget that no longer exists.
Mounted becomes false when dispose() is called, and attempting to call setState() on an unmounted State throws an error. This check is essential for preventing errors in async callbacks, timers, stream subscriptions, or any code that might execute after the widget is disposed. Always check mounted before setState() in async contexts.
