Getting type error from ng_repeat.dart

[yjbanov]

The type on the closure is wrong

https://github.com/angular/angular.dart/blob/a1d67aa9442a29b928950856f662b046468a6d5b/lib/directive/ng_repeat.dart#L134

[vicb]

Could you please give more details about this ?

It should get a CollectionChangeRecord when you are watching an iterable.

[yjbanov]

@chirayuk and @jbdeboer have the details, but basically this happens when the model bound to ng-repeat changes type from List to something other than a List. My situation goes roughly like this:

<div ng-if="ctrl.isList">
  <div ng-repeat="item in ctrl.data">{{item}}</div>
</div>
<div ng-if="!ctrl.isList">
  <div>{{ctrl.data}}</div>
</div>

When the type of ctrl.data changes, Angular still tries to evaluate ng-repeat incorrectly assuming ctrl.data is a list, when in fact it no longer is.

[vicb]

That's something we can fix in angular.dart but it could also be fixed in client code:
item in ctrl.getList() - where getList() would return null or const [], that would be more dartish

[yjbanov]

I don't understand your solution. Could you please use it on my example above?

[matanlurey]

Vic is suggesting in the ctrl.isList case, you use "item in ctrl.getList()" instead of accessing data directly, and have the getList() function do a guard and either return a null (or const[]) if the data is not of type List.

[vicb]

that's exactly what I was suggesting, let me know if anything is still unclear

[yjbanov]

Good workaround. Should still be fixed in Angular.

[vicb]

Should still be fixed in Angular.

What do other thinks ? I would not say this is a bug

[yjbanov]

How is the exception "type 'String' is not a subtype of type 'CollectionChangeRecord' of 'changes'" deep inside angular code not a bug?

[vicb]

You're right, this is a bug, we have two ways to fix it:

1. remove all rows when the type is not a CollectionChangeRecord,
2. throw a clearer exception.

To me getting someting other than a CollectionChangeRecord indicates a wrong usage and we should throw an exception, so I'm in favor of 2.

Thoughts ?

[yjbanov]

Could you describe what it is that's wrong with the usage?

[vicb]

The code is trying to iterate (ng-repeat) over a String while it can only iterate over a collection (List and Iterator IIRC)

[yjbanov]

If you look at the example above, the user's code is not trying to iterate over a String, because ng-repeat is guarded by ng-if.

[vicb]

If you look at the example above, the user's code is not trying to iterate over a String, because ng-repeat is guarded by ng-if.

This must be due to the evaluation order that you can not control which is why a think throwing "ng-repeat can not iterate over a 'String'" could help.

Notes:

• It is not very Dartish to put either a List or a String into the same variable,
• I'll take a look at the details for why ng-repeat is evaluated even if the condition is false.

[vicb]

@yjbanov I'm closing this issue as the last refactoring done for ng-repeat supports your use case (it would remove all rows when the subject is not Iterable).

I'll create a separate issue to investigate why ng-repeat is evaluated when it should not.