VariableBoundDecimalSlider.java

package variableEditorComponents;

import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.util.Observable;
import java.util.Observer;

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

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

/**
 * A JSlider which is bound to a Variable which contains a DecimalValue. When
 * the user moves the slider, the content of the Variable is updated. The scale
 * of the slider is also updated such that the value of the Variable is in the
 * middle of the slider range. When the Variable is changed from another source,
 * the scale of the slider is updated with the new contents of the Variable.
 * 
 * @author Curran Kelleher
 * 
 */
public class VariableBoundDecimalSlider extends JSlider implements
		ChangeListener, MouseListener, Observer, VariableEditorComponent {
	private static final long serialVersionUID = -7777499408692975081L;

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

	/**
	 * The resolution of the slider.
	 */
	final static int SLIDERSCALE = 800;

	/**
	 * The value at the lowest slider position
	 */
	double minValue = 0;

	/**
	 * The value at the highest slider position
	 */
	double maxValue = 10;

	/**
	 * A flag indicating to ignore slider changes. (set to true when change is
	 * self-induced)
	 */
	boolean ignoreSliderChange = false;

	/**
	 * A DecimalValue which is used many times as an intermediate for assigning
	 * a new value to the variable being edited. This is done to avoid creating
	 * many new Objects.
	 */
	DecimalValue reusableValue = new DecimalValue(0);

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

	/**
	 * The value corresponding to the highest (rightmost) slider position when
	 * the value of the Variable is zero.
	 */
	protected double maxValueForZeroValue = 1;

	/**
	 * The value corresponding to the lowest (leftmost) slider position when the
	 * value of the Variable is zero.
	 */
	protected double minValueForZeroValue = -1;

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

		// listen for the mouse release
		addMouseListener(this);

		// align the slider with our scale
		setMaximum(SLIDERSCALE);

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

		// initialize the slider
		updateWithCurrentVariableValue();

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

	/**
	 * Updates the range of values that the slider covers such that the current
	 * value of the variable makes it be in the center.
	 * 
	 */
	public void updateWithCurrentVariableValue() {
		double currentValue = DecimalValue.extractDoubleValue(variable
				.evaluate());
		maxValue = currentValue * 2;
		minValue = 0;

		if (maxValue == 0) {
			maxValue = maxValueForZeroValue;
			minValue = minValueForZeroValue;
		} else if (maxValue < 0) {
			minValue = maxValue;
			maxValue = 0;
		}
		// ignore the self-induced change
		ignoreSliderChange = true;
		// set the slider position
		setValue((int) ((currentValue - minValue) / (maxValue - minValue) * SLIDERSCALE));
		// don't ignore subsequent changes
		ignoreSliderChange = false;
		// update the displayed Value
		displayedValue = "" + currentValue;
	}

	/**
	 * Listens to slider changes, updates the variable's value
	 * 
	 * @param a
	 *            the event from the slider change
	 */
	public void stateChanged(ChangeEvent a) {
		if (!ignoreSliderChange) {
			reusableValue.value = getCurrentSliderValue();
			variable.set(reusableValue);
			displayedValue = reusableValue.toParseableString();
		}
	}

	/**
	 * 
	 * @return the current value (which the Variable will be set to) derived
	 *         from the slider position.
	 */
	protected double getCurrentSliderValue() {
		return minValue + ((double) getValue() / SLIDERSCALE)
				* (maxValue - minValue);
	}

	public void mouseClicked(MouseEvent e) {
	}

	public void mousePressed(MouseEvent e) {
	}

	/**
	 * Log the change when the mouse is released.
	 */
	public void mouseReleased(MouseEvent e) {
		// log the change for correct replay
		ExpressionConsoleModel.getInstance().enterExpression(
				variable.toString() + " = "
						+ variable.evaluate().toParseableString());
		updateWithCurrentVariableValue();
	}

	public void mouseEntered(MouseEvent e) {
	}

	public void mouseExited(MouseEvent e) {
	}

	/**
	 * 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))
				if (!getValueIsAdjusting())
					updateWithCurrentVariableValue();
	}

	/**
	 * Sets up a VariableEditorComponent such that
	 * updateWithCurrentVariableValue() will be called in it whenever the
	 * slider's position changes.
	 * 
	 * @param componentToUpdate
	 *            the VariableEditorComponent to update when the slider's
	 *            position changes.
	 */
	public void bindToVariableEditorComponent(
			VariableEditorComponent componentToUpdate) {
		final VariableEditorComponent componentToReallyUpdate = componentToUpdate;
		addChangeListener(new ChangeListener() {
			public void stateChanged(ChangeEvent e) {
				componentToReallyUpdate.updateWithCurrentVariableValue();
			}
		});
	}
}