How to keep business logic seperate within GWT Composites?

Question

Hi,

I'm currently building a GWT login screen and I managed to get a basic version of the login structure working.

I created the following pieces:

• An entry point class (actually it was given).
• A main application screen composite.
• A login-screen composite.

I have the following logic in my entry point method:

MyApplication mainWindow = null;
public void onModuleLoad() {
    LoginScreen loginScreen = new LoginScreen() {
        @Override
        public String onLogin(String username, String password) {
            boolean passwordWasOk = rpcCheckUsernamePassword(username,password); // mechanism not important for this question
            if (passwordWasOk) {
                RootPanel.get().remove(0);
                mainWindow = new MyApplication();
                // Using root layout panel as main window is a layout type composite
                RootLayoutPanel.get().add(mainWindow);
                return null;
            } else {
                return "password was incorrect";
            }
        }
    };
    RootPanel.get().add(loginScreen);
}

So, I created a method in the LoginScreen composite that is called when the user clicks the 'Sign-In' button. If the onLogin method fails its validation of the username and password, then a narrative can be returned to the login composite so that it can update the user. The login screen will stay on the screen until the user uses a correct username/password combination.

My question is, is this the correct way to use composites? Where should my login logic ideally reside. Is a better alternative to inject some sort of login handler object in the constructor of the composite or via a setter or is the method I used quite normal?

As I'm planning to write quite a lot of code, I want to get the coding style correct from the outset.

Any feedback is greatly appreciated.

Thanks,

Answer 1

For complex projects you'd want to use the Model-View-Presenter (MVP) design pattern. It allows you to separate the rendering logic (views) from the business logic. To get you started, the official documentation has two articles about it plus there's that presentation by Ray Ryan that started the whole GWT + MVP = <3 haze :) After that I'd recommend browsing through MVP related questions on SO and GWT's Google Group.