Question

Function canReveal() returns true if class ClientState has user information. If not, it first tries to get that user information using asyncronous call to GetUser. What I need to do inside the IF is to wait somehow until this asyncronous call returns (onSuccess), so that I can check whether ClientState has now the user information or not. How can I do that? Thanks

public class MyGatekeeper implements Gatekeeper{

private DispatchAsync dispatcher;

@Inject
public MyGatekeeper(DispatchAsync dispatcher) {
        this.dispatcher = dispatcher;
}

@Override
public boolean canReveal() {
    if(ClientState.isUserLoggedin()==false) {
        dispatcher.execute(new GetUser(Window.Location.getHref()),
        new DispatchCallback<GetUserResult>() {
                @Override
                        public void onSuccess(GetUserResult result) {
                if (!result.getErrorText().isEmpty()) {
                     Window.alert(result.getErrorText());
                     return;
                }
                ClientState.setUserInfo(result.getUserInfo());
            }
        });
        return ClientState.isUserLoggedin(); // WAIT till onSuccess returns!
    }
}
    return ClientState.isUserLoggedin();
}

Answer 1

The way to do this is to have canReveal take a Callback<Boolean>:

public void canReveal(Callback<Boolean> cb) {
  if (!ClientState.isUserLoggedIn()) {
    dispatcher.execute(..., new DispatchCallback<Result>() {
      @Override
      public void onSuccess(Result result) {
        cb.onSuccess(result.isGoodOrWhatever());
      }
    });
  } else {
    cb.onSuccess(true); // User is logged in
  }
}

Unfortunately there’s no way to tell GWT to “wait” for the async callback, since that would basically freeze JS execution, since JS is single-threaded.