Adding new tweens in callback functions is not allowed?

[playif]

I try to add some extra tweens in a callback function (i.e., when a tween completed).
However, since the other updating tweens occupy the _objects list in a forEach function, modifying the _object is not allowed.
Maybe you can add a new list (for those toBeAddedTweens), and pull the new tweens into _objects in the right timing?

[xaguzman]

Usually, how I have handled this is invoking either Timeline.createSequence() or Tween.to to create a totally new tween, have never seen an issue with it.

Are you trying to add tweens to an already existing timeline?

[playif]

Are you trying to add tweens to an already existing timeline?

No. Do you add new tweens in another tween's callback function?

[playif]

I made a simple reproduction by your simple_tween.dart example
Just change

    Tween.to(pos, VectorAccessor.XY, 1)
      ..delay = 0.3
      ..targetValues = [x, y]
      ..start(_tweenManager);

to

Tween.to(pos, VectorAccessor.XY, 1)
      ..delay = 0.3
      ..targetValues = [x, y]

      ..setCallback((int type, BaseTween source) {
      Tween.to(pos, VectorAccessor.XY, 2)
        ..delay = 0.3
        ..targetValues = [x, y]
        ..start(_tweenManager);
    })
      ..start(_tweenManager);

And you will get the error:
Uncaught Error: Concurrent modification during iteration: Instance(length:2) of '_GrowableList'.
Stack Trace:
#0 List.forEach (dart:core-patch/growable_array.dart:228)
#1 TweenManager.update (package:tweenengine/src/tween_manager.dart:99:25)
#2 SimpleTween.render (http://localhost:60000/tween-engine-dart-master/example/screens/simple_tween.dart:43:25)
#3 render (http://localhost:60000/tween-engine-dart-master/example/example.dart:63:23)
#4 _rootRunUnary (dart:async/zone.dart:730)
#5 _RootZone.runUnary (dart:async/zone.dart:864)
#6 _Future._propagateToListeners.handleValueCallback (dart:async/future_impl.dart:488)
#7 _Future._propagateToListeners (dart:async/future_impl.dart:571)
#8 _Future._complete (dart:async/future_impl.dart:317)
#9 _SyncCompleter.complete (dart:async/future_impl.dart:44)
#10 Window.animationFrame. (dart:html:29269)

Exception: Concurrent modification during iteration: Instance(length:2) of '_GrowableList'.

[xaguzman]

will look into it as soon as I can

[xaguzman]

fixed. Avoided applying the suggested fix to avoid allocating more lists into memory.
changing the foreach for a good old for fixed the issue

This will be up for for next version