CheckBox.java

package org.j4me.ui.components;

import javax.microedition.lcdui.*;
import org.j4me.ui.*;

/**
 * The <code>CheckBox</code> component lets a user turn an option on or off.
 * Multiple check box components can be placed sequentially to create
 * a list of choices where zero or more can be chosen.
 */
public class CheckBox
	extends Component
{
	/**
	 * The ratio of the side of the checkbox square to the height of
	 * the current font.
	 */
	private static final double CHECKBOX_TO_FONT_RATIO = 0.95;  // 70% 
	
	/**
	 * The text that appears to the right of the check box.
	 */
	private Label label = new Label();
	
	/**
	 * If the item is checked this will be <code>true</code>.  If the item
	 * is not this will be <code>false</code>.
	 */
	private boolean checked;
	
	/**
	 * Constructs a <code>CheckBox</code> component.
	 */
	public CheckBox ()
	{
	}

	/**
	 * Gets the value of the text that appears to the right of the check box.
	 * 
	 * @return The text that appears next to the check box.  It will
	 *  never be <code>null</code> but may be the empty string "".
	 */
	public String getLabel ()
	{
		String l = label.getLabel();
		
		if ( l == null )
		{
			l = "";
		}
		
		return l;
	}
	
	/**
	 * Sets the text that appears next to the check box.
	 * 
	 * @param value is the text that appears to the right of the check box.
	 *  A <code>null</code> is treated as the empty string "".
	 */
	public void setLabel (String value)
	{
		label.setLabel( value );
		
		// The label may change the size requirements of this component.
		invalidate();
	}
	
	/**
	 * Returns <code>true</code> if the box is checked or <code>false</code> if it is
	 * not.
	 * 
	 * @return <code>true</code> if the box is checked or <code>false</code> if it is
	 * not.
	 */
	public boolean isChecked ()
	{
		return checked;
	}
	
	/**
	 * Checks or unchecks the box.
	 * 
	 * @param checked when <code>true</code> checks the box; when <code>false</code>
	 *  unchecks it.
	 */
	public void setChecked (boolean checked)
	{
		this.checked = checked;
	}
	
	/**
	 * An event raised whenever the component is made visible on the screen.
	 * This is called before the <code>paintComponent</code> method.
	 */
	protected void showNotify ()
	{
		label.visible( true );
		super.showNotify();
	}

	/**
	 * An event raised whenever the component is removed from the screen.
	 */
	protected void hideNotify ()
	{
		label.visible( false );
		super.hideNotify();
	}

	/**
	 * Paints the check box component.
	 * 
	 * @see org.j4me.ui.components.Component#paintComponent(javax.microedition.lcdui.Graphics, org.j4me.ui.Theme, int, int, boolean)
	 */
	protected void paintComponent (Graphics g, Theme theme, int width, int height, boolean selected)
	{
		// Paint the check box.
		int checkboxSide = checkboxSideSize( theme );
		int y = (height - checkboxSide) / 2;
		
		int offset = paintRect( g, theme, 0, y, checkboxSide, checkboxSide, selected );
		
		// Paint the check in the box.
		if ( checked )
		{
			int checkColor = theme.getHighlightColor();
			g.setColor( checkColor );
			
			int checkOffset = offset + 1;
			int fillSide = checkboxSide - 2 * checkOffset;
			
			g.fillRect( checkOffset, y + checkOffset, fillSide, fillSide );
		}
		
		// Paint the text to the side of the box.
		int lx = (int)( checkboxSide * 1.5 );
		int lw = width - lx;
		
		int[] lDimensions = label.getPreferredSize( theme, lw, height );
		int lh = lDimensions[1];
		int ly = (height - lh) / 2;
		
		label.paint( g, theme, getScreen(), lx, ly, lw, lh, selected );
	}

	/**
	 * Returns the size of the checkbox sides.  It is a square so both sides have
	 * the same length.
	 * 
	 * @param theme is the current application theme.
	 * @return The number of pixels each side of the checkbox is.
	 */
	private int checkboxSideSize (Theme theme)
	{
		int fontHeight = theme.getFont().getHeight();
		int checkboxSide = (int)( fontHeight * CHECKBOX_TO_FONT_RATIO );
		return checkboxSide;
	}
	
	/**
	 * Returns the dimensions of the check box.
	 * 
	 * @see org.j4me.ui.components.Component#getPreferredComponentSize(org.j4me.ui.Theme, int, int)
	 */
	protected int[] getPreferredComponentSize (Theme theme, int viewportWidth, int viewportHeight)
	{
		// Get the height of the checkbox.
		int checkboxSide = checkboxSideSize( theme );
		
		// Get the height of the label to the right of the checkbox.
		int[] labelDimensions = label.getPreferredSize(
				theme, viewportWidth - checkboxSide, viewportHeight );

		// Return the bigger of the two heights.
		int height = Math.max( checkboxSide, labelDimensions[1] );
		
		// Make sure it is an even height.  Makes the checkbox look better.
		height += height % 2;
		
		return new int[] { viewportWidth, height };
	}
	
	/**
	 * @return <code>true</code> because this component accepts user input.
	 */
	public boolean acceptsInput ()
	{
		return true;
	}
	
	/**
	 * Called when a key is pressed.
	 * 
	 * @param keyCode is the key code of the key that was pressed.
	 */
	public void keyPressed (int keyCode)
	{
		// Was it an input character?
		//   Otherwise it was a menu button of special character.
		if ( (keyCode > 0) || (keyCode == DeviceScreen.FIRE) )
		{
			// Flip the box.
			checked = !checked;
			repaint();
		}
		
		// Continue processing the key event.
		super.keyPressed( keyCode );
	}
	
	/**
	 * Called when the pointer is pressed.
	 * 
	 * @param x is the horizontal location where the pointer was pressed
	 *  relative to the top-left corner of the component.
	 * @param y is the vertical location where the pointer was pressed
	 *  relative to the top-left corner of the component.
	 */
	public void pointerPressed (int x, int y)
	{
		// Flip the box.
		checked = !checked;
		repaint();
		
		// Continue processing the pointer event.
		super.pointerPressed( x, y );
	}
}