import java.awt.*;

import java.awt.event.*;

import javax.swing.*;

import javax.swing.event.*;

import javax.swing.plaf.basic.*;

/**

* 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 class BoundsPopupMenuListener implements PopupMenuListener

{

private boolean scrollBarRequired = true;

private boolean popupWider;

private int maximumWidth = -1;

private boolean popupAbove;

private JScrollPane scrollPane;

/**

* 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(true, 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;

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

if (child instanceof BasicComboPopup)

{

SwingUtilities.invokeLater(new Runnable()

{

public void run()

{

customizePopup((BasicComboPopup)child);

}

});

}

}

protected void customizePopup(BasicComboPopup popup)

{

scrollPane = getScrollPane(popup);

if (popupWider)

popupWider( popup );

checkHorizontalScrollBar( popup );

// For some reason in JDK7 the popup will not display at its preferred

// width unless its location has been changed from its default

// (ie. for normal "pop down" shift the popup and reset)

Component comboBox = popup.getInvoker();

Point location = comboBox.getLocationOnScreen();

if (popupAbove)

{

int height = popup.getPreferredSize().height;

popup.setLocation(location.x, location.y - height);

}

else

{

int height = comboBox.getPreferredSize().height;

popup.setLocation(location.x, location.y + height - 1);

popup.setLocation(location.x, location.y + height);

}

}

/*

* Adjust the width of the scrollpane used by the popup

*/

protected void popupWider(BasicComboPopup popup)

{

JList list = popup.getList();

// 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

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);

scrollPane.revalidate();

}

}

/*

* 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.getInvoker();

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 popupMenuCanceled(PopupMenuEvent e) {}

@Override

public void popupMenuWillBecomeInvisible(PopupMenuEvent e)

{

// In its normal state the scrollpane does not have a scrollbar

if (scrollPane != null)

{

scrollPane.setHorizontalScrollBar( null );

}

}

}