deliveryChanges does not work with Dart2 (with solution)

[jodinathan]

Extend ChangeNotifier with your own ChangeRecord, like:

class MyRecord extends ChangeRecord {
}
class MyClass extends ChangeNotifier<MyRecord> {
}

once you add some notifications, dart throws an error on:

bool deliverChanges() {
    List<ChangeRecord> changes;
    ...
    _changes.add(changes); // this will throw an error of mismatched types
}

The only thing you need to do to solve it is change this line:

bool deliverChanges() {
    List<ChangeRecord> changes;

to this:

bool deliverChanges() {
    List<C> changes;

[natebosch]

I assume you're seeing the issue at runtime in DDC? what version of the SDK are you on?

[jodinathan]

sorry.
DDC
dev-24 and dev-28 neither worked

[natebosch]

If we change the type to List<C> then I think the assignment to ChangeRecord.ANY would fail.

https://github.com/dart-lang/observable/blob/bc4b2d9902099e459ea744b8969239156c65623f/lib/src/change_notifier.dart#L61

ChangeRecord.ANY is a List<ChangeRecord> which is not a List<C>

https://github.com/dart-lang/observable/blob/bc4b2d9902099e459ea744b8969239156c65623f/lib/src/records.dart#L22

I think this is likely to be a bit tougher to solve and I'm not sure if we have the bandwidth to dig deeply on it...

[jodinathan]

yeah, just tested it and it threw an error with ANY.
that is probably why it was List<ChangeRecord> in the first place.

Maybe just sending an empty instead of the ANY const?
afterall, that dummy ChangeRecord wasn't much of a help.

Or you can store the last queue and send it again if the new queue is empty.

[kevmoo]

CC @nshahan

[jodinathan]

For now I am using my fork: https://github.com/jodinathan/observable
It basically changes:

https://github.com/dart-lang/observable/blob/bc4b2d9902099e459ea744b8969239156c65623f/lib/src/change_notifier.dart#L55

to:
List<C> changes;

and

https://github.com/dart-lang/observable/blob/bc4b2d9902099e459ea744b8969239156c65623f/lib/src/change_notifier.dart#L61

to:

changes = <C>[];

It is a breaking change, however, that empty ChangeRecord from ANY const has no value at all.

[shamblett]

Hi guys, any update on this as far as a permanent fix is concerned, I'd rather use observable if a fix is forthcoming.

[kevmoo]

@nshahan ?

[nshahan]

I'll do some testing on our codebase to see if we can easily fix up any breaks.

[buhhy]

I've created a pull request to fix this issue:

#76

[wsakka]

Not sure why the flutter team leaves these issues open -- it's been a year, what's the status of this issue?

[jodinathan]

@wsakka it has been fixed with version 0.22.1+5.
I am closing this issue.