Using a Provider in a showModalBottomSheet – Flutter

It is perfectly fine to add multiple providers or use MultiProvider above MaterialApp, it’s actually the right thing to do for global dependencies.

There is a documented potential performance hit if you’re using MultiProvider to nest a lot of dependencies. This is less to do with widget tree performance but the hit you’re taking with instantiating a lot of widgets at once.

As the documentation explains, there are ways around this including splitting your dependencies up and loading them based on state or simply avoiding MultiProvider. Your question specifically asks about wrapping your MaterialApp with multiple ChangeNotifierProviders instead of using MultiProvider so I think you’re good in that regard.

A more thorough explanation to your question is that your Providers need to be inserted above a Navigator for new routes that you push on the stack, either with Navigator.push, showModalBottomSheet, or by modifying Navigator.pages depending on which navigation style your using, to be able to access those Providers through the context.

MaterialApp builds your "root" Navigator which is why they need to be above MaterialApp. If you’re using the pattern of nested navigation, something we employee a lot in apps I work on, you’ll need to make sure any Providers you want in that particular nested Navigator are above that Navigator. Besides being able to reuse these "inner journey", you can tailor the dependencies (Providers or other InheritedWidgets) needed for these navigation trees, allowing you to only inject what is needed where.