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55 lines
2.5 KiB
55 lines
2.5 KiB
5 years ago
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# provider_shopper
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A Flutter sample app that shows a state management approach using the [Provider][] package.
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This is the app discussed in the [Simple app state management][simple] section of
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[flutter.dev][].
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[Provider]: https://pub.dev/packages/provider
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[simple]: https://flutter.dev/docs/development/data-and-backend/state-mgmt/simple
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[flutter.dev]: https://flutter.dev/
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## Goals for this sample
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* Show simple use of `Provider` for providing an immutable value to a subtree
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* Illustrate a simple state management approach using the ChangeNotifier class
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* Show use of `ProxyProvider` for provided objects that depend on other provided objects
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## The important bits
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### `lib/main.dart`
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Here the app sets up objects it needs to track state: a catalog and a shopping cart. It builds
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a `MultiProvider` to provide both objects at once to widgets further down the tree.
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The `CartModel` instance is provided using a `ChangeNotifierProxyProvider`, which combines
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two types of functionality:
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1. It will automatically subscribe to changes in `CartModel` (if you only want this functionality
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simply use `ChangeNotifierProvider`).
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2. It takes the value of a previously provided object (in this case, `CatalogModel`, provided
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just above), and uses it to build the value of `CartModel` (if you only want
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_this_ functionality, simply use `ProxyProvider`).
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### `lib/models/*`
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This directory contains the model classes that are provided in `main.dart`. These classes
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represent the app state.
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### `lib/screens/*`
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This directory contains widgets used to construct the two screens of the app: the catalog and
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the cart. These widgets have access to the current state of both the catalog and the cart
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via `Provider.of`.
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## Questions/issues
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If you have a general question about Provider, the best places to go are:
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* [Provider documentation](https://pub.dev/documentation/provider/latest/)
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* [StackOverflow](https://stackoverflow.com/questions/tagged/flutter)
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If you run into an issue with the sample itself, please file an issue
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in the [main Flutter repo](https://github.com/flutter/flutter/issues).
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