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September 13, 2024 06:31
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Dart Riverpod: merging two providers of the same type to emit the latest value
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| import 'package:riverpod/riverpod.dart'; | |
| /// Dart Riverpod merging two providers of the same type | |
| /// https://stackoverflow.com/questions/78978863/dart-riverpod-merging-two-providers-of-the-same-type | |
| // Example StateNotifier for a simple counter. | |
| class Counter extends Notifier<int> { | |
| @override | |
| int build() => 0; | |
| void increment() => state++; | |
| } | |
| // Create multiple providers of the same type. | |
| final counterProvider1 = NotifierProvider<Counter, int>(Counter.new); | |
| final counterProvider2 = NotifierProvider<Counter, int>(Counter.new); | |
| // Create a provider that combines the latest values. | |
| final mergeCounterProvider = Provider<int>((ref) { | |
| final sub = ref.listen(counterProvider1, (_, value) => ref.state = value); | |
| ref.listen(counterProvider2, (_, value) => ref.state = value); | |
| return sub.read(); | |
| }); | |
| void main() { | |
| final container = ProviderContainer(); | |
| print(container.read(mergeCounterProvider)); // 0 | |
| container.read(counterProvider1.notifier).increment(); | |
| container.read(counterProvider1.notifier).increment(); | |
| print(container.read(mergeCounterProvider)); // 2 | |
| container.read(counterProvider2.notifier).increment(); | |
| print(container.read(mergeCounterProvider)); // 1 | |
| } |
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