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、易管理比较简单。如果它被混合在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晰。）如果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，代码是更加容易的打包成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 =
(caption==FORWARD_YEAR )? loader.getResource(NEXT_YEAR):
(caption==BACK_YEAR )? loader.getResource(PREVIOUS_YEAR):
(caption==FORWARD_MONTH )? loader.getResource(NEXT_MONTH):
loader.getResource(PREVIOUS_MONTH) ;
JButton b = (image!=null) ? new JButton( new ImageIcon(image) )
: new JButton(caption)
;
b.setBorder(new EmptyBorder(0,4,0,4));
b.setFocusPainted(false);
b.setActionCommand(caption);
b.addActionListener( navigation_listener );
b.setOpaque( false );
return b;
}
public synchronized void addActionListener(ActionListener l)
{ selector.addActionListener(l);
}
public synchronized void removeActionListener(ActionListener l)
{ selector.removeActionListener(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); }
}
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