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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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