Mvc how does model update view

If the state of this data changes, then the model will usually notify the view so the display can change as needed and sometimes the controller if different logic is needed to control the updated view.

Going back to our shopping list app, the model would specify what data the list items should contain — item, price, etc. In our shopping list app, the view would define how the list is presented to the user, and receive the data to display from the model. So for example, our shopping list could have input forms and buttons that allow us to add or delete items. These actions require the model to be updated, so the input is sent to the controller, which then manipulates the model as appropriate, which then sends updated data to the view.

The mouseDragged method adds the point from the MouseEvent to the model and repaints the window. The valueChanged method obtains the selected color from the view the event object is not very useful, plus the view knows what the colors are , updates the model's color, and repaints the window. A DemoView object has instance variables for the window's components, plus two class constants for the color selection: an array of Strings to be displayed, and an array of Colors corresponding to the Strings.

DemoView is a subclass of JFrame. The constructor organizes the window, and the methods help to coordinate with the controller and the model. The PaintPanel is added to the "center" so that it will use up available space. The registerListener method is used to register the controller with the specific components that the user interacts with.

The getSelectedColor method allows the controller to find out what color in the JList was selected by the user. The paint method might be a little mysterious because there is no paint method call in the code. This method will be called as part of a call to the repaint method see the methods in DemoController. No code should directly call the paint method.

The paint method sets the background color of the JPanel that contains the JList calls super. PaintPanel implements the rest of the view. It is used to draw the points that the user has drawn. PaintPanel extends JPanel and overrides the paintComponent method to draw the points. This method loops through all the Points in the model. From my understanding, we shouldn't have the model depend on the controller as it would we would create a bidirectional dependency between the components, which can lead to unmaintainable code and difficulty adding changes.

So, I imagine the bidirectional relationship to communicate as the following:. However, if we create an interface for the model to communicate with the controller, IController , it can remove this bidirectional communication.

IController implements all the methods that notify the controller changes. The dependency would look like the following:. Now, the model is ignorant of the actual implementations of the controller. Therefore, changes in the controller, should not affect the model components. I was wondering if adding an interface for the controller the best way for model and controller to communicate with each other. I am also aware that in some programs, the model can directly communicate with the view directly using the observer design pattern.

However, the model should not know the implementation details of the view since the model should be respected with high-level policy and should not know about low-level policies, such as the view.

Therefore, in this case, let's not consider the observer pattern for the model to communicate the view. Thus the model has no need for any dependency on anything. You can even go further and get rid of the View's dependency on the Model, by creating and populating it in the Controller.

Which is standard for web applications. These methods do give you a problem for the case where the Model updates outside of a Controller event. For example, lets say the model has a Time property which updates automatically to the system time every second.

In these cases you will wish to update the view without having a controller event. This can be achieved by a number of methods. Obviously the best solution is to avoid these types of uncaused changes in your Model. For example. It uses a Model the html that is downloaded from the web server. It has a View the part where we read the downloaded html.

It has a controller the scroll bar or even the selection parts that lets you set the size larger on the screen or not… So, you have one component that mixes the View and the Controller together.

JTable is the exact same. Regards, Nate. Hey, now. Maybe this will help you?