VariableBoundCheckBox.java

package variableEditorComponents;

import java.awt.event.ItemEvent;
import java.awt.event.ItemListener;
import java.util.Observable;
import java.util.Observer;

import javax.swing.JCheckBox;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;

import valueTypes.BooleanValue;
import variableEditorUI.VariableEditorUIUpdateThread;
import variables.Variable;
import expressionConsole.ExpressionConsoleModel;

/**
 * A JCheckBox which is bound to a Variable. When the user checks or unchecks
 * the box, the content of the Variable is updated. When the Variable is changed
 * from another source, the state of the box is updated with the new contents of
 * the Variable.
 * 
 * @author Curran Kelleher
 * 
 */
public class VariableBoundCheckBox extends JCheckBox implements Observer,
		ItemListener, VariableEditorComponent {
	private static final long serialVersionUID = -7777499408692975081L;

	/**
	 * The Variable to which this VariableBoundCheckBox is bound.
	 */
	Variable variable;

	/**
	 * The Value that is currently being displayed. This is checked against the
	 * actual value of the Variable periodically to decide whether or not to
	 * update the display. This String is parseable into the actual value. It is
	 * generated by the method Value.toParseableString()
	 */
	String displayedValue = "";

	/**
	 * set true to ignore self-generated checkbox events
	 */
	boolean ignoreUpdates = false;

	/**
	 * Construct a VariableBoundCheckBox which is bound to the specified Variable.
	 * 
	 * @param variable
	 *            the variable to edit
	 */
	public VariableBoundCheckBox(Variable variable) {
		super(variable.toString());
		this.variable = variable;

		// get notifications every second.
		VariableEditorUIUpdateThread.getInstance().addObserver(this);

		// initialize the check box
		updateWithCurrentVariableValue();

		// listen for slider movements
		addItemListener(this);
	}

	/**
	 * Updates the content of the check box to reflect the current value of the
	 * variable.
	 * 
	 */
	public void updateWithCurrentVariableValue() {
		ignoreUpdates = true;
		setSelected(BooleanValue.extractBooleanValue(variable.evaluate()));
		displayedValue = variable.evaluate().toParseableString();
		ignoreUpdates = false;
	}

	/**
	 * Get the update from the VariableEditorUIUpdateThread
	 */
	public void update(Observable o, Object arg) {
		if (o == VariableEditorUIUpdateThread.getInstance())
			// if this component is no longer usable, remove it as an Observer.
			if (!isDisplayable())
				VariableEditorUIUpdateThread.getInstance().deleteObserver(this);
			else if (!variable.evaluate().toParseableString().equals(
					displayedValue))
				updateWithCurrentVariableValue();
	}

	/**
	 * Respond to check box changes
	 */
	public void itemStateChanged(ItemEvent e) {
		if (!ignoreUpdates) {
			variable.set(new BooleanValue(
					e.getStateChange() == ItemEvent.SELECTED));
			// log the change for correct replay
			displayedValue = variable.evaluate().toParseableString();
			ExpressionConsoleModel.getInstance().enterExpression(
					variable.toString() + " = " + displayedValue);
		}
	}

	/**
	 * Sets up a VariableEditorComponent such that
	 * updateWithCurrentVariableValue() will be called in it whenever the
	 * checkbox is checked or unchecked.
	 * 
	 * @param componentToUpdate
	 *            the VariableEditorComponent to update.
	 */
	public void bindToVariableEditorComponent(
			VariableEditorComponent componentToUpdate) {
		class ComponentChangeListener implements ChangeListener {
			VariableEditorComponent componentToUpdate;

			public ComponentChangeListener(
					VariableEditorComponent componentToUpdate) {
				this.componentToUpdate = componentToUpdate;
			}

			public void stateChanged(ChangeEvent e) {
				componentToUpdate.updateWithCurrentVariableValue();
			}
		}
		addChangeListener(new ComponentChangeListener(componentToUpdate));
	}
}