Observing rebuilds

When you instantiate your store, you can optionally pass it a modelObserver that you can use to visualize rebuilds.

warning

This is a power feature only useful for creators of developer tools. Feel free to skip this page.

The ModelObserver is an abstract class with an observe method you can override to be notified, by each StoreConnector currently in the widget tree, whenever there is a state change. You can create your own ModelObserver, but the provided DefaultModelObserver can be used out of the box to print to the console and do basic testing:

var store = Store<AppState>(
  initialState: state,
  modelObserver: DefaultModelObserver(),  
);

This is an example output to the console, showing how MyWidgetConnector responded to 3 state changes:

Model D:1 R:1 = Rebuid:true, Connector:MyWidgetConnector, Model:MyViewModel{B}.
Model D:2 R:2 = Rebuid:false, Connector:MyWidgetConnector, Model:MyViewModel{B}.
Model D:3 R:3 = Rebuid:true, Connector:MyWidgetConnector, Model:MyViewModel{C}.

You can see above that the first and third state changes resulted in a rebuild (Rebuid:true), but the second one did not, probably because the part of the state that changed was not in MyViewModel.

Note: You must pass debug: this as a StoreConnector constructor parameter, if you want the ModelObserver to be able to print the StoreConnector type to the output. You can also override your ViewModel.toString() to print out any extra info you need.

The ModelObserver is also useful when you want to create tests to assert that rebuilds happen when and only when the appropriate parts of the state change. For an example, see the Model Observer Test.