使用Decorator模式实现日期选择组件(4)

1/5/2008来源:Java教程人气:5571


  标题
  这Date_selector_panel是重要部分。现在我们来看看他的装饰。Titled_date_selector类只做一件事情:给未装饰的日历增加个标题。这是对实现了Date_selector的JPanel面板的包装。它只显示现有的Date_selector和显示日期的标签。下面的实现是微不足道。和用户界面无相关值得说的只有那其中10行动作监听代码。监听器获取日期改变通知(通过用户导航或者方法调用)便做相应的标签日期更新。其他代码只是简单地创建面板和将Date_selector与JLable标题包装进面板中。
  这表明这部分代码易写、易治理比较简单。假如它被混合在Date_selector_panel中,将会在 没有明显的优点的情况下增加了代码的复杂度。(代码有组织地放在某处比全混合在一个地方更加清楚。)假如我想要标题更加美观,只需要修改这一个类即可以实现根本就不需要动其他部分。
  
  public class Titled_date_selector extends JPanel implements Date_selector
  {  PRivate    Date_selector selector;
    private final JLabel title = new JLabel("XXXX");
  
    /** Wrap an existing Date_selector to add a title bar showing
     * the displayed month and year. The title changes as the
     * user navigates.
     */
  
    public Titled_date_selector( Date_selector selector )
    {  this.selector = selector;
  
      title.setHorizontalAlignment(SwingConstants.CENTER);
      title.setOpaque   ( true                   );
      title.setBackground ( com.holub.ui.Colors.LIGHT_YELLOW     );
      title.setFont    ( title.getFont().deriveFont( Font.BOLD )  );
  
      selector.addActionListener
      (  new ActionListener()
        {  public void actionPerformed( ActionEvent e )
          {  if( e.getID() == Date_selector_panel.CHANGE_ACTION )
              title.setText( e.getActionCommand() );
            else
              my_subscribers.actionPerformed(e);
          }
        }
      );
  
      setOpaque(false);
      setLayout( new BorderLayout() );
      add( title, BorderLayout.NORTH );
      add( (JPanel)selector, BorderLayout.CENTER );
    }
  
    /** This constrUCtor lets you specify the background color of the
     * title strip that holds the month name and year (the default
     * is light yellow).
     *
     * @param label_background_color the color of the title bar, or
     *   null to make it transparent.
     */
    public Titled_date_selector( Date_selector selector, Color label_background_color )
    {  this(selector);
      if( label_background_color == null )
        title.setOpaque( false );
      else
        title.setBackground( label_background_color );
    }
  
    private ActionListener my_subscribers = null;
    public synchronized void addActionListener(ActionListener l)
    {  my_subscribers = AWTEventMulticaster.add(my_subscribers, l);
    }
    public synchronized void removeActionListener(ActionListener l)
    {  my_subscribers = AWTEventMulticaster.remove(my_subscribers, l);
    }
  
    public Date get_selected_date()   { return selector.get_selected_date(); }
    public Date get_current_date()   { return selector.get_current_date();  }
    public void roll(int f, boolean up) {    selector.roll(f,up);      }
    public int get(int f)       { return selector.get(f);        }
  }
  
  NAVIGATION/导航
  下面展示的就是导航栏的实现代码,虽然有点长,但同样非常地简单。代码由定义了4个图象文件的代码开始。(我计划以后放弃箭头采用代码实现,但是现在仍然在用图象文件。)用下面的代码,把图象作为资源获取过来。
  ClassLoader loader = getClass().getClassLoader();
  loader.getResource( "IMAGE_FILE_NAME" );
  classloader在找类的地方找图象资源;比如,程序在文件系统中运行,它将要在classpath中查找文件路径。因为没有用到绝对路径,代码是更加轻易的打包成jar文件,并且文件也不再需要建立在文件系统中。导航栏是一个四个用图象做标签的按纽,按纽的动作监听通过Date_selector的roll()来包装日历对象,并且月份的改变也激发标题栏的改变。有一点非常重要就是导航条不知道也不影响标题。标题包装器是一个监听,所以它能自动的更新标题。导航条根本就不知道标题包装器的存在。
  
  public class Navigable_date_selector extends JPanel implements Date_selector
  {  private    Date_selector selector;
  
    // Names of image files used for the navigator bar
    private static final String
      NEXT_YEAR    = "images/10px.red.arrow.right.double.gif",
      NEXT_MONTH   = "images/10px.red.arrow.right.gif",
      PREVIOUS_YEAR  = "images/10px.red.arrow.left.double.gif",
      PREVIOUS_MONTH = "images/10px.red.arrow.left.gif";
  
    // These constants are used to identify the button and
    // as the button caption in the event that the appropriate
    // image file can't be located
  
    private static final String FORWARD_MONTH  = ">"  ,
                  FORWARD_YEAR  = ">>"  ,
                  BACK_MONTH   = "<"  ,
                  BACK_YEAR    = "<<"  
  
    private JPanel navigation = new JPanel();
  
    public Navigable_date_selector( Date_selector selector )
    {  this.selector = selector;
      setBorder( null );
      setOpaque( false );
      setLayout( new BorderLayout() );
      add( (JPanel)selector, BorderLayout.CENTER );
  
      navigation.setLayout(new FlowLayout());
      navigation.setBorder( null );
      navigation.setBackground( com.holub.ui.Colors.LIGHT_YELLOW );
      navigation.add( make_navigation_button(BACK_YEAR  ) );
      navigation.add( make_navigation_button(BACK_MONTH  ) );
      navigation.add( make_navigation_button(FORWARD_MONTH) );
      navigation.add( make_navigation_button(FORWARD_YEAR ) );
  
      add(navigation, BorderLayout.SOUTH);
    }
  
    // ...
    // I left out a few constructors and utility methods that go here
    // ...
  
    private final Navigation_handler navigation_listener
                      = new Navigation_handler();
  
    /** Handle clicks from the navigation bar buttons */
  
    private class Navigation_handler implements ActionListener
    {  public void actionPerformed(ActionEvent e)
      {  String direction = e.getActionCommand();
  
        if   (direction==FORWARD_YEAR )selector.roll(Calendar.YEAR,true);
        else if(direction==BACK_YEAR  )selector.roll(Calendar.YEAR,false);
        else if(direction==FORWARD_MONTH)
        {
          selector.roll(Calendar.MONTH,true);
          if( selector.get(Calendar.MONTH) == Calendar.JANUARY )
            selector.roll(Calendar.YEAR,true);
        }
        else if (direction==BACK_MONTH )
        {
          selector.roll(Calendar.MONTH,false);
          if( selector.get(Calendar.MONTH) == Calendar.DECEMBER )
            selector.roll(Calendar.YEAR,false);
        }
        else
        {  assert false: "UneXPected direction";
        }
      }
    }
  
    private JButton make_navigation_button(String caption)
    {
      ClassLoader loader = getClass().getClassLoader();
      URL image =
        (cap