在GWT中，为什么约定使用asWidget（）而不是强制转换？

Question

I'm new to GWT. In the code examples I've seen, the presenter defines an interface Display that includes the asWidget method. For example,

public interface Display {
   HasClickHandlers getSaveButton();
   HasValue<String> getName();
   ...
   Widget asWidget();
}

Then the presenter implements the go() method:

public void go(final HasWidgets container){
   ...
   container.add(display.asWidget());
}

What's wrong with just casting the display to a Widget, eg

container.add((Widget) display);

Thank you!

Answer 1

asWidget() is in GWT in order to facilitate testing.

With it you can use stub implementations of displays and other view components in your tests without having to extends the abstract class Widget.

So in your case, your display can be any class, not necessarily a Widget, the only condition is that it returns a Widget.

Here you can read a more complete explanation.