menu.java

关于J4ME J2ME实例

package org.j4me.ui;

import org.j4me.ui.components.*;

/**
 * The <code>Menu</code> class is used for creating the application's menus.
 * <p>
 * J2ME devices have small screens and are not all very responsive to scrolling.
 * However, they do have keypads.  The <code>Menu</code> class respects this and
 * limits menus to a total of 9 possible choices (1-9) plus "Exit".  Usually all
 * the choices can be seen on a single screen and selected with a single button.
 * <p>
 * Override this class to change how the menu is painted for your application.
 */
public class Menu
	extends Dialog
{
	/**
	 * The screen that invoked this one or <code>null</code> if there is no
	 * previous screen.
	 */
	protected DeviceScreen previous;
	
	/**
	 * Constructs a menu.
	 */
	public Menu ()
	{
		// No spacing between components.
		//   The MenuOption component will add spacing for us.
		setSpacing( 0 );
		
		// Add the menu bar.
		Theme theme = UIManager.getTheme();
		String rightMenuText = theme.getMenuTextForOK();
		setMenuText( null, rightMenuText );
	}
	
	/**
	 * Constructs a menu.
	 * 
	 * @param name is the title for this menu, for example "Main Menu".  It
	 *  appears at the top of the screen in the title area.
	 * @param previous is the screen to return to if the user cancels this.
	 */
	public Menu (String name, DeviceScreen previous)
	{
		this();
		
		this.previous = previous;

		setTitle( name );
		setPrevious( previous );
	}
	
	/**
	 * Sets the screen to return to if the user cancels this menu.  If
	 * <code>previous</code> is <code>null</code>, there will be no "Cancel" button.
	 * 
	 * @param previous is the screen to go to if the user presses "Cancel".
	 */
	public void setPrevious (DeviceScreen previous)
	{
		// Record the previous screen.
		this.previous = previous;

		// Set the menu text.
		Theme theme = UIManager.getTheme();
		String leftMenuText = (previous == null ? null : theme.getMenuTextForCancel());
		String rightMenuText = theme.getMenuTextForOK();
		setMenuText( leftMenuText, rightMenuText );
	}
	
	/**
	 * Appends a new menu option to this menu.
	 * 
	 * @param option is the menu item to add.
	 */
	public void appendMenuOption (MenuItem option)
	{
		MenuOption choice = new MenuOption( option );
		append( choice );
	}
	
	/**
	 * Appends a screen as a menu option.  If selected the screen will be
	 * shown.  The screen's title is used as its text.
	 * 
	 * @param option is screen to add as a menu item.
	 */
	public void appendMenuOption (DeviceScreen option)
	{
		MenuOption choice = new MenuOption( option );
		append( choice );
	}
	
	/**
	 * Appends a screen as a menu option.  If selected the screen will be
	 * shown.
	 * 
	 * @param text is string that appears in the menu option.
	 * @param option is screen to add as a menu item.
	 */
	public void appendMenuOption (String text, DeviceScreen option)
	{
		MenuOption choice = new MenuOption( text, option );
		append( choice );
	}
	
	/**
	 * Appends another menu as a menu option.  The submenu will have an
	 * arrow next to it to indicate to the user it is another menu.
	 * <p>
	 * To use a <code>Menu</code> as a screen and not a submenu call the
	 * <code>appendMenuOption</code> method instead.
	 * 
	 * @param submenu is the screen to add as a menu item.
	 */
	public void appendSubmenu (Menu submenu)
	{
		MenuOption choice = new MenuOption( submenu, true );
		append( choice );
	}
	
	/**
	 * The left menu button takes the user back to the previous screen.
	 * If there is no previous screen it has no effect.
	 */	
	protected void declineNotify ()
	{
		// Go back to the previous screen.
		if ( previous != null )
		{
			previous.show();
		}

		// Continue processing the event.
		super.declineNotify();
	}

	/**
	 * The right menu button selects the highlighted menu item.
	 */	
	protected void acceptNotify ()
	{
		// Go to the highlighted screen.
		int highlighted = getSelected();
		selection( highlighted );

		// Continue processing the event.
		super.acceptNotify();
	}

	/**
	 * Responds to key press events that are specific to menu screens.
	 * Selects the highlighted menu choice if the joystick's
	 * <code>FIRE</code> key is pressed.  Scrolls from the last choice to
	 * the first choice if <code>DOWN</code> is pressed and from the first to
	 * the last if <code>UP</code> is pressed.
	 * 
	 * @param key is the key code of the button the user pressed.
	 */
	protected void keyPressed (int key)
	{
		boolean goToFirst = false;
		boolean goToLast = false;
		
		// Wrap the scroll around the screen?
		if ( key == DOWN )
		{
			if ( getSelected() == size() - 1 )
			{
				// Go to the first menu choice.
				goToFirst = true;
			}
		}
		else if ( key == UP )
		{
			if ( (getSelected() == 0) && (size() > 1) )
			{
				// Go to the last menu choice.
				goToLast = true;
			}
		}

		// Process the key event.
		super.keyPressed( key );

		// Were we going to the first or last menu choice?
		//   Only do these after super.keyPressed().  Otherwise
		//   keyPressed() will scroll again so we'll actually wind
		//   up on the second or second-to-last menu choice.
		if ( goToFirst )
		{
			setSelected( 0 );
		}
		else if ( goToLast )
		{
			setSelected( size() - 1 );
		}
	}
	
	/**
	 * Selects a menu item.
	 * 
	 * @param selection is the index of <code>choice</code> that is selected.
	 */
	private void selection (int selection)
	{
		Component component = get( selection );
		
		if ( component instanceof MenuOption )
		{
			MenuOption chosen = (MenuOption)component;
			
			// Record this as the selection.
			setSelected( selection );
			
			// Perform the selection operation.
			chosen.select();
		}
	}
}