how to implement MVC pattern for word guessing gam

问题:

I have some working code for the word guessing game. But I fear it does not confine the design rules especially the MVC pattern. The attached image is my GUI currently. I am throwing around objects from one class to another and I hear that it is a bad style. while I agree with that, I am not able to come up with good MVC pattern approach for the word guessing game or the Hangman commonly called. The main application will have some like this:

public class Application {

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {

            @Override
            public void run() {
                runApp();
            }

        });
    }

    public static void runApp() {
        Model model = new Model();
        View view = new View(model); //not sure if this correct, some suggest it is valid and some not

        Controller controller = new Controller(view, model);
    }

}

how would I approach this? The GUI as seen in the attached picture would be the View Class. This includes all JButtons, Textfield, borders, labels etc. Attach actionlisteners to JButtons in the View class

The controller will pass the events to the model. for example, if some letter buttons are clicked, it would pass that letter "A" is clicked to model and the model will either send instructions to controller to update view or it will update view directly. from my understanding of the MVC pattern, the model class must be implemented and tested separately from view and controller. I do not understand how I can achieve this here. I have complete code available. I need to refactor to confine to MVC pattern. kindly pass on your suggestions.

回答1:

I think one of the areas you are getting confused over is "responsibility". What is each component responsible for and what can it actually do.

The problem isn't that you are passing Objects around you program, but more that the objects you are passing are exposing parts of your application that the recipient has no business knowing about or should be allowed to manipulate.

What I mean by this is, if you were to pass the "buttons" panel to the "guess" panel, because you wanted to have the ability to allow the "guess" panel detect when a button was clicked, you've exposed the "buttons" panel to an area of your application that has no right to actually see it.

What's stopping the "guess" panel from removing components? Nothing...

Instead, we should use interfaces which determine what each part of the application can and can't do and what information is available to it.

This is where you model comes in. The model determines what information is available, how it can be accessed and what events might be triggered to notify interested parties that the model has changed.

For example. Your "buttons" panel would tell the model that the user has made another guess (in response to the user pressing the button). The model would then raise an event, which would notify the "guess" panel that a change has occurred. The "guess" panel then would update it's state accordingly, asking the model for the information it needed in order to represent the current state of the model (as far as it was responsible for).

You could take a look at

• Code to Interface, Access by name and Instance Data
• Program to an interface

Now, with the MCV pattern, the view must be able to see the model, the controller must be able to see the view and model and the model doesn't care.

The controller is listening for changes to the view (ie user interactions), which it passes to the model. The model fires notifications about changes to it's state and the view responds to those changes by updating itself as required.

For example, the use clicks a button on the "button" panel. The "button" panel's controller detects this event (probably via an ActionListener), it process this action and updates the model.

The model updates it's internal state and fires some kind of event.

The "guess" panel detects this change in the model (via some kind of listener) and updates it's view accordingly (update the guess's and the image as dictated by the model).

Now, remember, Swing doesn't use a pure MCV pattern, it's controls (ie buttons) are both the controller and the view, so just be careful when playing around with these...

I would start with a HangManModel interface which defines all the properties you want to expose, such as the guesses, the "secret" word and perhaps the number of incorrect guesses made and the state of the game (win or lose) for example.

I would also define the listeners that might be registered to the model, which describes the events that this model can generate. You could use a PropertyChangeListener or even a ChangeListener or define your own, based on your own needs, for example...

public interface HangManModel {

    public void addGuess(char guess);

    public char[] getGuesses();
    public String getSecretWord();
    public int getState(); // running, win or lose

    public void addChangeListener(ChangeListener listener);
    public void removeChangeListener(ChangeListener listener);

}

Now this is just an example, personally, I might be tempered to hide the secret word and expose properties about it (like it's length for example). You could also be tempted to provide a setter for the secret word, so the model could be reset...

This would represent the "heart" of your application, around this, you would build your views and controllers.

回答2:

EDIT : Working example of MVC (netbeans project, made by me) is download here or download here. Who does not know netbeans : in dist is executable .jar file and in src are sources. It shows MVC pattern with two different views. On the left, you can left or right click to create circle or square and on the right you can see these squares and circles in table. You can change value (like size or position) of square or circle in table and it is updated into model which updates view so on the left you can see how that square or circle moved or resized.

You have good approach, but you got few things wrong. This is a basic, simple model of MVC :

As here you can see, the model DOES NOT send anything into the controller.

How to build MVC application? Mabye better start with the model. The model should have everything except the input/output handling. All the data, all the logic.

So you should have 3 main classes : Controller, View, Model.

For example you just create form with button which in each hit add one "A" letter into the middle of form.

In View class, you have update method, which paints and/or repaints the count of "A" letters into the form.

When you hit the button, it jumps into the method buttonClicked. This calls method on controller, saying that controller what just happend. Controller see that and manipulates data in the model (in this example calls the method addA). After this, model should know that he was changed, so he call update method on the connected view class which repaints the count of "A" printed in the middle of form.

Addition

You can have multiple views for one model! We can add one more view, which in top-left corner of form prints the number of "A" used. Model can have list of view instead of just view and when changed, he just updates all of them.

Pseudocode

public class Application {
    private Model model = new Model();
    private Controller controller = new Controller();
    private View view = new View();

    public Application(){
        model.registerView(view);
        controller.registerModel(model);
        view.registerController(controller);
    }
}

回答3:

Interestion question... So far I heard about MVP and MVVM design patterns used whithin desktop apps, but I have never seen MVC for this type of apps. However, I just took Spring MVC (the best java web framework) and tryed to apply it on desktop apps.

1. I would create a front controller that handles all events for the app.
2. This controller gets an event and sends it to EventResolver.
3. EventResolver returns back the name or something of a method and class which will play a "controller" role to the front controller.
4. After the front controller creates an instance of this class and calls a method.
5. In the method body you call some business logic and return model and id for ViewResolver to the front Controler. 6 Again the front controller analyzes the result and calls an approperiate ViewResolver.

Yes, this is how spring MVC works and I just copied it) But why not to use the best!

回答4:

There's lots of different flavors of MVC, but they all share the same general idea.

The first thing to understand is exactly what the model is. The job of the model is to handle all the logical code. So in this case, the model will track which letters have been guessed, what the word to guess is, whether the game is over, and how many pieces of the stick man are showing.

Basically, you should be able to simulate the game in its entirety just from function calls into the model.

There's a few ways to pass information from the model to the view. The view could poll the model periodically to see if anything has updated. This method is not very elegant. A simple way that is often effective for small-scale projects is to pass a View object into the Model object and whenever anything changes in the model, refresh everything in the view. It's no big deal for a smaller UI to do this. Finally, you can create a Listener registration system (Observer pattern) to have specific parts of the View subscribe to specific events in the model. This method is what I've done for larger UI projects.

The controller's job is to pass user input to the model. For this reason, the controller and view can often be defined in the same classes. This is okay! It's much better to have your JButtons have a click method that calls the model directly rather than telling some Controller class to pass it on to the model.