future.dart

// You must wait until the controller is initialized before displaying the
// camera preview. Use a FutureBuilder to display a loading spinner until the
// controller has finished initializing.
FutureBuilder<void>(
  future: _initializeControllerFuture,
  builder: (context, snapshot) {
    if (snapshot.connectionState == ConnectionState.done) {
      // If the Future is complete, display the preview.
      return CameraPreview(_controller);
    } else {
      // Otherwise, display a loading indicator.
      return Center(child: CircularProgressIndicator());
    }
  },
)