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RText is a powerful, cross-platform programmer's text editor written in Java. It is designed to be easy to use, highly customizable and flexible. Part of RText's design is for the source code to be simple, easy to understand, and well documented, so that other programmers can look into its inner-workings and figure out how RText ticks with ease. A good place to start (besides the source code) is the Javadoc for all classes used in the project.

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/*
 * 06/13/2009
 *
 * AssistanceIconPanel.java - A panel that sits alongside a text component,
 * that can display assistance icons for that component.
 * Copyright (C) 2009 Robert Futrell
 * robert_futrell at users.sourceforge.net
 * http://fifesoft.com
 *
 * This file is a part of RText.
 *
 * RText is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or any later version.
 *
 * RText is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
 */
package org.fife.ui.search;

import java.awt.BorderLayout;
import java.awt.Component;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.event.FocusEvent;
import java.awt.event.FocusListener;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;
import java.util.ResourceBundle;

import javax.swing.Icon;
import javax.swing.ImageIcon;
import javax.swing.JComboBox;
import javax.swing.JComponent;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.SwingConstants;
import javax.swing.text.JTextComponent;


/**
 * A panel meant to be displayed alongside a text component, that can display
 * assistance icons for that text component.
 *
 * @author Robert Futrell
 * @version 1.0
 */
class AssistanceIconPanel extends JPanel
						implements FocusListener, PropertyChangeListener {

	/**
	 * The width of this icon panel, to help align the components we're
	 * listening to with other combos or text fields without an
	 * AssistanceIconPanel.
	 */
	public static final int WIDTH		= 8;

	private JLabel iconLabel;
	private boolean showIcon;

	/**
	 * The tooltip text for the light bulb icon.  It is assumed that access
	 * to this field is single-threaded (on the EDT).
	 */
	private static String ASSISTANCE_AVAILABLE;


	/**
	 * Constructor.
	 *
	 * @param combo The combo box to listen to.
	 */
	public AssistanceIconPanel(JComponent comp) {

		setLayout(new BorderLayout());
		iconLabel = new JLabel(EmptyIcon.INSTANCE);
		iconLabel.setVerticalAlignment(SwingConstants.TOP);
		add(iconLabel, BorderLayout.NORTH);

		if (comp instanceof JComboBox) {
			JComboBox combo = (JComboBox)comp;
			Component c = combo.getEditor().getEditorComponent();
			if (c instanceof JTextComponent) { // Always true
				JTextComponent tc = (JTextComponent)c;
				tc.addFocusListener(this);
			}
		}
		else { // Usually a JTextComponent
			comp.addFocusListener(this);
		}

		comp.addPropertyChangeListener(
			ContentAssistable.ASSISTANCE_IMAGE, this);

	}


	/**
	 * Called when the combo box or text component gains focus.
	 *
	 * @param e The focus event.
	 */
	public void focusGained(FocusEvent e) {
		showIcon = true;
		iconLabel.repaint();
	}


	/**
	 * Called when the combo box or text component loses focus.
	 *
	 * @param e The focus event.
	 */
	public void focusLost(FocusEvent e) {
		showIcon = false;
		iconLabel.repaint();
	}


	/**
	 * Returns the "Content Assist Available" tooltip text for the light bulb
	 * icon.  It is assumed that this method is only called on the EDT.
	 *
	 * @return The text.
	 */
	static String getAssistanceAvailableText() {
		if (ASSISTANCE_AVAILABLE==null) {
			ResourceBundle msg = ResourceBundle.getBundle(
											"org.fife.ui.search.Search");
			ASSISTANCE_AVAILABLE = msg.getString("ContentAssistAvailable");
		}
		return ASSISTANCE_AVAILABLE;
	}


	/**
	 * Paints any child components.
	 *
	 * @param g The graphics context.
	 */
	protected void paintChildren(Graphics g) {
		if (showIcon) {
			super.paintChildren(g);
		}
	}


	/**
	 * Called when the property
	 * {@link ContentAssistable#ASSISTANCE_IMAGE} is fired by the component
	 * we are listening to.
	 *
	 * @param e The change event.
	 */
	public void propertyChange(PropertyChangeEvent e) {
		Image img = (Image)e.getNewValue();
		if (img==null && iconLabel.getIcon()!=EmptyIcon.INSTANCE) {
			iconLabel.setIcon(EmptyIcon.INSTANCE);
			iconLabel.setToolTipText(null);
		}
		else {
			iconLabel.setIcon(new ImageIcon(img));
			iconLabel.setToolTipText(getAssistanceAvailableText());
		}
	}


	/**
	 * An empty icon.
	 */
	private static class EmptyIcon implements Icon {

		private static final EmptyIcon INSTANCE = new EmptyIcon();

		public int getIconHeight() {
			return WIDTH;
		}

		public int getIconWidth() {
			return WIDTH;
		}

		public void paintIcon(Component c, Graphics g, int x, int y) {
		}
		
	}


}