adding callback functions so that default app bar can communicate with search bar

default_app_bar.dart

// add this method to default app bar class
// this will get executed when user pressed back arrow on search bar
cancelSearch() {
  // remove search bar from stack
  setState(() {
    isInSearchMode = false;
  });

  // change search value to ''
  onSearchQueryChange('');
  
  // run the rippple animation in reverse direction
  _controller.reverse();
}

// add this method to default app bar class
onSearchQueryChange(String query) {
  // do anything with this string you can pass it back to Scaffold and 
  // handle it there as well, it's up to you
  print('search $query');
}

// pass these callback functions to SearchBar in render method of DefaultAppBar
SearchBar(
  onCancelSearch: cancelSearch,
  onSearchQueryChanged: onSearchQueryChange,
)