Add ComputedNotifier streaming class
#150143
Conversation
`ComputedNotifier` is a new `ValueListenable` implementation that computes its value based on other `ValueListenable` instances. This facilitates efficient and reactive updates for derived state, eliminating the need for manual dependency tracking and update propagation. The class listens to changes from provided dependencies and recomputes its value whenever any of them change, notifying its listeners only when the computed value itself changes.
Clarifies that `ComputedNotifier` is also a preferred alternative to `Stream` subclasses, aligning with the preference for `ValueNotifier` and `ChangeNotifier` in Flutter framework code.
| /// final ValueNotifier<int> b = ValueNotifier<int>(2); | ||
| /// | ||
| /// final ComputedNotifier<int> sum = ComputedNotifier<int>( | ||
| /// [a, b, c, d], |
There was a problem hiding this comment.
Why listen to c and d if only a and b are used in compute?
| /// | ||
| /// Additionally, it is important to dispose of the listeners that are passed | ||
| /// to the constructor when they are no longer needed. | ||
| /// |
| @@ -61,13 +61,15 @@ class Counter with ChangeNotifier { | |||
| } | |||
|
|
|||
| void main() { | |||
| testWidgets('ChangeNotifier can not dispose in callback', (WidgetTester tester) async { | |||
| testWidgets('ChangeNotifier can not dispose in callback', | |||
There was a problem hiding this comment.
Can you please undo the formatting changes in this file?
| /// | ||
| /// final ComputedNotifier<int> sum = ComputedNotifier<int>( | ||
| /// [a, b, c, d], | ||
| /// () => a.value + b.value, |
There was a problem hiding this comment.
What worries me about this API design: It's gonna be very easy to use a listenable in the compute function and accidentally forget to include it in the listenable list...
There was a problem hiding this comment.
You're absolutely right!! But although I think it might happen, I am not very worried about that.. It's a basic programming skill issue, not very related to the API signature.
Also, in some cases, you might not want to include all values used in the computed callback in your listenable list, right?
But, what do you think we can do to improve it? Besides a clear documentation..
There was a problem hiding this comment.
Maybe we can return the listenable list as a parameter in our callback, so it can reinforces the user to add the listenable to the list:
final ComputedNotifier<String> sum = ComputedNotifier<int>(
<ValueListenable<int>>[a, b],
(List<ValueListenable<dynamic>> list) => ((list.first.value as int) + (list[1].value as int)).toString(),
);To be honest, I do not found this a good solution. Maybe because I don't see it as a ruge problem.
There was a problem hiding this comment.
You made me intriguer about a solution for this... what do you think about write the API as this?
final ValueNotifier<int> a = ValueNotifier<int>(1);
final ValueNotifier<int> b = ValueNotifier<int>(2);
final ComputedNotifier<int> sum = ComputedNotifier<int>(
(ValueGetter getter) => getter(a) + getter(b),
);
int sumValue = sum.value;
sum.addListener(() => sumValue = sum.value);
a.value = 2;
print(sumValue); // 4
b.value = 3;
print(sumValue); // 5|
@goderbauer PTAL |
Introduce
ComputedNotifier, a newValueListenableimplementation that computes its value based on otherValueListenableinstances. This facilitates efficient and reactive updates for derived state, eliminating the need for manual dependency tracking and update propagation.The class listens to changes from provided dependencies and recomputes its value whenever any of them change, notifying its listeners only when the computed value itself changes.
No issue found for this PR
Pre-launch Checklist
///).If you need help, consider asking for advice on the #hackers-new channel on Discord.