package framework;

import javax.swing.*;
import javax.swing.event.*;
import java.awt.event.*;
import java.awt.*;
import java.util.*;

/**
  The base class for all views.
  <p>
  Programmers should extend this class with any panel that
  displays the model.
  <p>
  Example:
  <pre>
     class PieChartView extends AppView {
        public PieChartView(MyModel m) {
	       super(m);
	       display();
	    }
	    public void update(Observable o, Object arg) {
	       display();
	    }
	    private void display() {
	       MyModel m = (MyModel)model;
	       // draw a pie chart of the data in m
	    }
    }
    </pre>
  */
public class AppView extends JPanel implements Observer {
    /**
     The model that this view displays
     */
    protected Model model;
    /**
     Initializes model.
     Adds this view as an observer to the new model and
     deletes it as an observer to the previous model.

     @param m  the new model
     */
    public AppView(Model m) {
		setModel(m);;
	}
	/**
	 This does not initialize the model.
	 Programmers must call setModel.
	 */
	public AppView() {  }
    /**
     Sets the model to a new model.
     Deletes this view from the observers of the old model.
     Adds this view to the observers of the new model.

     @param m  The new model
     */
	public void setModel(Model m) {
		if (model != null) {
			model.deleteObserver(this);
		}
		model = m;
		model.addObserver(this);
	}
    /**
     This method is indirectly called by Model.notifyViews.
     <p>
     The implementation is empty. Programmers should override
     this method in subclasses so that it fetches new data
     from the model and redraws the view.
     */
	public void update(Observable o, Object arg) { }

}