[ovirt-devel] Frontend - please avoid putting business logic into Views

Hi guys, our GWT frontend generally follows the Model-View-Presenter design pattern via GWT-Platform MVP module [1]. [1] https://github.com/ArcBees/GWTP/wiki/Getting-started Presenters/PresenterWidgets should be the ones containing the business logic. Views should only contain simple logic to perform necessary UI updates etc. Consider the following example of imaginary "Foo" dialog: // inside FooPopupView.java @Override public void edit(SomeModel model) { // this is OK! driver.edit(model); // please DON'T do this! model.getSomeAttribute().getEntityChangedEvent().addListener(...); } There are two main reasons why to avoid adding listeners to given model (i.e. SomeModel) inside View.edit() method: 1, MVP pattern encourages putting business logic into Presenter (reflecting Presenter's responsibility) 2, View.edit()'s responsibility is to populate UI from model data, and can be potentially called multiple times! Following example shows the "correct" (MVP-ish) way: // inside FooPopupPresenterWidget.java public interface ViewDef extends ... { // in your listener, you can use getView().doSomething() void doSomething(); } @Override public void init(SomeModel model) { // listeners are added only once, as they should! model.getSomeAttribute().getEntityChangedEvent().addListener(...); } This applies to both PresenterWidgets (typically dialogs) and "regular" Presenters (typically main/sub tabs etc). Also, please avoid explicit View impl. type casts inside Presenters/PresenterWidgets: // inside FooPopupPresenterWidget.java // please DON'T do this! ((FooPopupView) getView()).doSomething(); // you should use this! getView().doSomething(); Just modify the ViewDef interface to contain methods you need to invoke on the View. Please remember that ViewDef is THE interface between Presenter and View. Please avoid referencing specific View implementation inside Presenter. Let me know if you have any questions. Regards, Vojtech