BoundsPopupMenuListener.java

package jav.gui.token.edit;

/**
 *
 * @author http://tips4java.wordpress.com/2010/11/28/combo-box-popup/
 */
import java.awt.Container;
import java.awt.Dimension;
import java.awt.Point;
import javax.swing.*;
import javax.swing.event.PopupMenuEvent;
import javax.swing.event.PopupMenuListener;
import javax.swing.plaf.basic.BasicComboPopup;

/**
 *  This class will change the bounds of the JComboBox popup menu to support
 *  different functionality. It will support the following features:
 *  -  a horizontal scrollbar can be displayed when necessary
 *  -  the popup can be wider than the combo box
 *  -  the popup can be displayed above the combo box
 *
 *  Class will only work for a JComboBox that uses a BasicComboPop.
 */
public abstract class BoundsPopupMenuListener implements PopupMenuListener
{
	private boolean scrollBarRequired = true;
	private boolean popupWider;
	private int maximumWidth = -1;
	private boolean popupAbove;

	/**
	 *  Convenience constructore to allow the display of a horizontal scrollbar
	 *  when required.
	 */
	public BoundsPopupMenuListener()
	{
		this(true, false, -1, false);
	}

	/**
	 *  Convenience constructor that allows you to display the popup
	 *  wider and/or above the combo box.
	 *
	 *  @param popupWider when true, popup width is based on the popup
	 *                    preferred width
	 *  @param popupAbove when true, popup is displayed above the combobox
	 */
	public BoundsPopupMenuListener(boolean popupWider, boolean popupAbove)
	{
		this(false, popupWider, -1, popupAbove);
	}

	/**
	 *  Convenience constructor that allows you to display the popup
	 *  wider than the combo box and to specify the maximum width
	 *
	 *  @param maximumWidth the maximum width of the popup. The
	 *                      popupAbove value is set to "true".
	 */
	public BoundsPopupMenuListener(int maximumWidth)
	{
		this(true, true, maximumWidth, false);
	}

	/**
	 *  General purpose constructor to set all popup properties at once.
	 *
	 *  @param scrollBarRequired display a horizontal scrollbar when the
	 *         preferred width of popup is greater than width of scrollPane.
	 *  @param popupWider display the popup at its preferred with
	 *  @param maximumWidth limit the popup width to the value specified
	 *         (minimum size will be the width of the combo box)
	 *  @param popupAbove display the popup above the combo box
	 *
	 */
	public BoundsPopupMenuListener(
		boolean  scrollBarRequired, boolean popupWider, int maximumWidth, boolean popupAbove)
	{
		setScrollBarRequired( scrollBarRequired );
		setPopupWider( popupWider );
		setMaximumWidth( maximumWidth );
		setPopupAbove( popupAbove );
	}

	/**
	 *  Return the maximum width of the popup.
	 *
	 *  @return the maximumWidth value
	 */
	public int getMaximumWidth()
	{
		return maximumWidth;
	}

	/**
	 *  Set the maximum width for the popup. This value is only used when
	 *  setPopupWider( true ) has been specified. A value of -1 indicates
	 *  that there is no maximum.
	 *
	 *  @param maximumWidth  the maximum width of the popup
	 */
	public void setMaximumWidth(int maximumWidth)
	{
		this.maximumWidth = maximumWidth;
	}

	/**
	 *  Determine if the popup should be displayed above the combo box.
	 *
	 *  @return the popupAbove value
	 */
	public boolean isPopupAbove()
	{
		return popupAbove;
	}

	/**
	 *  Change the location of the popup relative to the combo box.
	 *
	 *  @param popupAbove  true display popup above the combo box,
	 *                     false display popup below the combo box.
	 */
	public void setPopupAbove(boolean popupAbove)
	{
		this.popupAbove = popupAbove;
	}

	/**
	 *  Determine if the popup might be displayed wider than the combo box
	 *
	 *  @return the popupWider value
	 */
	public boolean isPopupWider()
	{
		return popupWider;
	}

	/**
	 *  Change the width of the popup to be the greater of the width of the
	 *  combo box or the preferred width of the popup. Normally the popup width
	 *  is always the same size as the combo box width.
	 *
	 *  @param popupWider  true adjust the width as required.
	 */
	public void setPopupWider(boolean popupWider)
	{
		this.popupWider = popupWider;
	}

	/**
	 *  Determine if the horizontal scroll bar might be required for the popup
	 *
	 *  @return the scrollBarRequired value
	 */
	public boolean isScrollBarRequired()
	{
		return scrollBarRequired;
	}

	/**
	 *  For some reason the default implementation of the popup removes the
	 *  horizontal scrollBar from the popup scroll pane which can result in
	 *  the truncation of the rendered items in the popop. Adding a scrollBar
	 *  back to the scrollPane will allow horizontal scrolling if necessary.
	 *
	 *  @param scrollBarRequired  true add horizontal scrollBar to scrollPane
	 *                            false remove the horizontal scrollBar
	 */
	public void setScrollBarRequired(boolean scrollBarRequired)
	{
		this.scrollBarRequired = scrollBarRequired;
	}

	/**
	 *  Alter the bounds of the popup just before it is made visible.
	 */
	@Override
	public void popupMenuWillBecomeVisible(PopupMenuEvent e)
	{
		JComboBox comboBox = (JComboBox)e.getSource();

		if (comboBox.getItemCount() == 0) return;

		Object child = comboBox.getAccessibleContext().getAccessibleChild(0);

		if (child instanceof BasicComboPopup)
		{
			customizePopup((BasicComboPopup)child);
		}
	}

	protected void customizePopup(BasicComboPopup popup)
	{
		if (popupWider)
			popupWider( popup );

		checkHorizontalScrollBar( popup );

		if (popupAbove)
			popupAbove( popup );
	}

	/*
	 *  Adjust the width of the scrollpane used by the popup
	 */
	protected void popupWider(BasicComboPopup popup)
	{
		JList list = popup.getList();
		JScrollPane scrollPane = getScrollPane(popup);

		//  Determine the maximimum width to use:
		//  a) determine the popup preferred width
		//  b) limit width to the maximum if specified
		//  c) ensure width is not less than the scroll pane width

		int popupWidth = list.getPreferredSize().width
					   + 5  // make sure horizontal scrollbar doesn't appear
					   + getScrollBarWidth(popup, scrollPane);

		if (maximumWidth != -1)
		{
			popupWidth = Math.min(popupWidth, maximumWidth);
		}

		Dimension scrollPaneSize = scrollPane.getPreferredSize();
		popupWidth = Math.max(popupWidth, scrollPaneSize.width);

		//  Adjust the width

		scrollPaneSize.width = popupWidth;
		scrollPane.setPreferredSize(scrollPaneSize);
		scrollPane.setMaximumSize(scrollPaneSize);
	}

	/*
	 *  This method is called every time:
	 *  - to make sure the viewport is returned to its default position
	 *  - to remove the horizontal scrollbar when it is not wanted
	 */
	private void checkHorizontalScrollBar(BasicComboPopup popup)
	{
		//  Reset the viewport to the left

		JScrollPane scrollPane = getScrollPane(popup);
		JViewport viewport = scrollPane.getViewport();
		Point p = viewport.getViewPosition();
		p.x = 0;
		viewport.setViewPosition( p );

		//  Remove the scrollbar so it is never painted

		if (! scrollBarRequired)
		{
			scrollPane.setHorizontalScrollBar( null );
			return;
		}

		//	Make sure a horizontal scrollbar exists in the scrollpane

		JScrollBar horizontal = scrollPane.getHorizontalScrollBar();

		if (horizontal == null)
		{
			horizontal = new JScrollBar(JScrollBar.HORIZONTAL);
			scrollPane.setHorizontalScrollBar( horizontal );
			scrollPane.setHorizontalScrollBarPolicy( JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED );
		}

		//	Potentially increase height of scroll pane to display the scrollbar

		if (horizontalScrollBarWillBeVisible(popup, scrollPane))
		{
			Dimension scrollPaneSize = scrollPane.getPreferredSize();
			scrollPaneSize.height += horizontal.getPreferredSize().height;
			scrollPane.setPreferredSize(scrollPaneSize);
			scrollPane.setMaximumSize(scrollPaneSize);
		}
	}

	/*
	 *	Size of the popup has been adjusted now we can change its
	 *  location to display above the combo box.
	 */
	protected void popupAbove(BasicComboPopup popup)
	{
		Point parent = ((JComboBox) popup.getAccessibleContext().getAccessibleParent()).getLocationOnScreen();
		int height = popup.getPreferredSize().height;
		popup.setLocation(parent.x, parent.y - height);
	}

	/*
	 *  Get the scroll pane used by the popup so its bounds can be adjusted
	 */
	protected JScrollPane getScrollPane(BasicComboPopup popup)
	{
		JList list = popup.getList();
		Container c = SwingUtilities.getAncestorOfClass(JScrollPane.class, list);

		return (JScrollPane)c;
	}

	/*
	 *  I can't find any property on the scrollBar to determine if it will be
	 *  displayed or not so use brute force to determine this.
	 */
	protected int getScrollBarWidth(BasicComboPopup popup, JScrollPane scrollPane)
	{
		int scrollBarWidth = 0;
		JComboBox comboBox = (JComboBox) popup.getAccessibleContext().getAccessibleParent();

		if (comboBox.getItemCount() > comboBox.getMaximumRowCount())
		{
			JScrollBar vertical = scrollPane.getVerticalScrollBar();
			scrollBarWidth = vertical.getPreferredSize().width;
		}

		return scrollBarWidth;
	}

	/*
	 *  I can't find any property on the scrollBar to determine if it will be
	 *  displayed or not so use brute force to determine this.
	 */
	protected boolean horizontalScrollBarWillBeVisible(BasicComboPopup popup, JScrollPane scrollPane)
	{
		JList list = popup.getList();
		int scrollBarWidth = getScrollBarWidth(popup, scrollPane);
		int popupWidth = list.getPreferredSize().width + scrollBarWidth;

		return popupWidth > scrollPane.getPreferredSize().width;
	}

	@Override
	public void popupMenuWillBecomeInvisible(PopupMenuEvent e) {}
}