not able to set focus on TextBox in a GWT app

问题:

This should not be causing me so much pain but it is. It is a very weird problem. In a GWT application, I have two .java files, login.java and application.java. In login.java, I'm creating a user login page where if the username and password is verified the user is logged into the application and application.java takes from here.

Now in application. java's onModuleLoad() this is how i'm starting with a login page.

public void onModuleLoad() {
  Login login = new Login();
  login.textBoxUsername.setFocus(true);
  RootLayoutPanel.get().add(login);}

This works great, except for the tiny problem of not being able to set focus on the username TextBox when the page loads. I have tried evrything I can think of. But the focus just doesn't get set on the TextBox. If anyone can suggest a solution, please do. Your help is greatly appreciated.

Solution: (In case it helps anyone facing the same issue)

final Login login = new Login();
  Scheduler.get().scheduleDeferred(new ScheduledCommand() {
        public void execute () {
            login.textBoxUsername.setFocus(true);
        }
   });

  RootLayoutPanel.get().add(login);

回答1:

Try using Scheduler.scheduleDeferred():

public void onModuleLoad() {
    Login login = new Login();
    Scheduler.get().scheduleDeferred(new Scheduler.ScheduledCommand () {
        public void execute () {
            login.textBoxUsername.setFocus(true);
        }
    });
    RootLayoutPanel.get().add(login);       
}

Update: answer updated to use Scheduler.get().scheduleDeferred() instead of DeferredCommand, which is deprecated.

回答2:

Why using DefferedCommand, I think it's better to use someWidget.getElement().focus() which is a native Javascript. I'm using it everywhere, I've not seen any problem.

回答3:

If your Widget extends Composite, you can:

@Override
protected void onAttach() {
    super.onAttach();
    textBoxUsername.setFocus(true);
}

回答4:

It would be so easy for GWT to store a 'wantsFocus' in the internal state, and call focus after the widget is attached. We are still waiting after many years for that feature however...

Still, even after the attach handler is called, setFocus does not always work.

So in the meantime, our GwtUtil library has used the following code. It is a combination of several other solutions, and has been wrapped in a utility function:

static public void setFocus(final FocusWidget focusWidget) {
    if (focusWidget.isAttached()) {
        Scheduler.get().scheduleDeferred(new Scheduler.ScheduledCommand() {
            @Override
            public void execute() {
                focusWidget.setFocus(true);
            }
        });
    } else {
        focusWidget.addAttachHandler(new AttachEvent.Handler() {
            @Override
            public void onAttachOrDetach(AttachEvent event) {
                if (event.isAttached()) {
                    Scheduler.get().scheduleDeferred(new Scheduler.ScheduledCommand() {
                        @Override
                        public void execute() {
                            focusWidget.setFocus(true);
                        }
                    });
                }
            }
        });
    }
}

And call it like this:

setFocus(myTextBox);

It makes sense to use a utility function; If and when GWT finally makes setFocus work, you won't have to change your source code in multiple places.