customitem.java

用于移动设备上的java虚拟机源代码

/*
 * @(#)CustomItem.java	1.62 02/09/12 @(#)
 *
 * Copyright (c) 2002 Sun Microsystems, Inc.  All rights reserved.
 * PROPRIETARY/CONFIDENTIAL
 * Use is subject to license terms.
 */

package javax.microedition.lcdui;

import java.lang.String;

import com.sun.midp.lcdui.Text;

/**
 * A CustomItem is customizable by subclassing to introduce new visual and
 * interactive elements into <code>Forms</code>. 
 * Subclasses are responsible for their visual
 * appearance including sizing and rendering and choice of colors, fonts and
 * graphics.  Subclasses are responsible for the user interaction mode by
 * responding to events generated by keys, pointer actions, and traversal
 * actions.  Finally, subclasses are responsible for calling {@link
 * Item#notifyStateChanged} to trigger notification of listeners that the
 * <code>CustomItem's</code> value has changed.
 *
 * <p>Like other <code>Items</code>, <code>CustomItems</code>
 * have the concept of <em>minimum</em> and
 * <em>preferred</em> sizes.  These pertain to the total area
 * of the <code>Item</code>,
 * which includes space for the content, label, borders, etc.  See <a
 * href="Item.html#sizes">Item Sizes</a> for a full discussion of the
 * areas and sizes of <code>Items</code>.</p>
 *
 * <p><code>CustomItem</code> subclasses also have the concept
 * of the <em>content</em> size, which is the size of only the
 * content area of the <code>CustomItem</code>.  The
 * content area is a rectangular area inside the total area occupied by the
 * <code>CustomItem</code>.
 * The content area is the area within which the <code>CustomItem</code>
 * subclass paints and receives input events.  It does not include space
 * consumed by labels and borders.  The implementation is responsible for
 * laying out, painting, and handling input events within the area
 * of the <code>Item</code> that is outside the content area.</p>
 *
 * <p>All coordinates passed between the implementation and
 * the <code>CustomItem</code>
 * subclass are relative to the item's content area, with the upper-left
 * corner of this area being located at <code>(0,0)</code>. 
 * Size information passed
 * between the implementation and the <code>CustomItem</code> subclass with the
 * 
 * {@link #getMinContentHeight getMinContentHeight},
 * {@link #getMinContentWidth getMinContentWidth},
 * {@link #getPrefContentHeight getPrefContentHeight},
 * {@link #getPrefContentWidth getPrefContentWidth}, and
 * {@link #sizeChanged sizeChanged}
 * 
 * methods all refer to the size of the content area.  The implementation is
 * responsible for computing and maintaining the difference between the size
 * of the content area and the size of the total area of the
 * <code>Item</code> as reported by the Item size methods
 * 
 * {@link Item#getMinimumHeight Item.getMinimumHeight},
 * {@link Item#getMinimumWidth Item.getMinimumWidth},
 * {@link Item#getPreferredHeight Item.getPreferredHeight}, and
 * {@link Item#getPreferredWidth Item.getPreferredWidth}.</p>
 *
 * <p>The implementation may disregard sizing information returned from a
 * <code>CustomItem</code> if it exceeds limits imposed by the
 * implementation's user interface policy.  In 
 * this case, the implementation must always report the actual size granted to 
 * the <code>CustomItem</code> via the {@link #sizeChanged sizeChanged}
 * and the {@link #paint paint} methods.
 * For example, this situation may occur if the implementation
 * prohibits an <code>Item</code> from becoming wider than the screen.  If the
 * <code>CustomItem</code> subclass code returns a value from
 * <code>getMinContentWidth</code> that would result in the
 * <code>CustomItem</code> being wider than the screen, the implementation may 
 * assign a width smaller than the minimum width returned by
 * <code>getMinContentWidth</code>.</p>
 *
 * <p>The implementation is allowed to call the <code>CustomItem's</code> 
 * content size methods
 * 
 * {@link #getMinContentHeight getMinContentHeight},
 * {@link #getMinContentWidth getMinContentWidth},
 * {@link #getPrefContentHeight getPrefContentHeight}, and
 * {@link #getPrefContentWidth getPrefContentWidth},
 * 
 * in any order with respect to other <code>CustomItem</code> methods.
 * For all of these methods, the <code>CustomItem</code> subclass code must
 * return values that are consistent with the current contents of the
 * <code>CustomItem</code>.  If the contents changes, it is not sufficient for
 * the <code>CustomItem</code> subclass code simply to begin returning
 * different values from the content size methods.  Instead, the subclass code
 * must call the {@link #invalidate invalidate} method whenever its contents
 * changes.  This indicates to the implementation that it may need to perform
 * its layout computation, which will call the content size methods to get new
 * values based on the <code>CustomItem's</code> new contents.</p>
 * 
 * <a name="interaction"></a>
 * <h2>Interaction Modes</h2>
 * <p>The <code>CustomItem</code> class is intended to allow 
 * edit-in-place on many items,
 * but it does not allow every conceivable interaction.  Desire for
 * flexibility has been balanced against a requirement that these APIs be
 * simple enough to master easily, along with a need to allow for
 * platform-specific variations in look-and-feel, all without sacrificing
 * interoperability.</p>
 *
 * <p>The general idea is that there are multiple interaction
 * &quot;modes&quot; and that the <code>Form</code> 
 * implementation can convey which
 * ones it supports.  The <code>CustomItem</code> can then choose to
 * support one or more interaction modes.  There is no requirement for a
 * <code>CustomItem</code> to implement all combinations of
 * all interaction modes.
 * Typically, a <code>CustomItem</code> will implement an 
 * approach (such as the separate
 * editing screen technique discussed below) that works on all platforms,
 * in addition to a highly interactive approach that relies on a particular
 * interaction mode.  At run time, the <code>CustomItem</code>
 * code can query the system
 * to determine whether this interaction mode is supported.  If it is, the
 * <code>CustomItem</code> can use it; otherwise, it will fall
 * back to the approach that works on all platforms. </p>
 *
 * <p><code>CustomItem</code> can always use item commands to invoke
 * a separate editing screen,
 * although components with a small number of discrete
 * states could simply respond by changing the state and
 * then causing an <code>notifyStateChanged</code> notification. 
 * A technique for using a
 * separate editing screen would be to load the value into another
 * <code>Displayable</code> object (such as a List) and then to call
 * {@link Display#setCurrent(Displayable)} on it.
 * When the user
 * issues a command (such as &quot;OK&quot;) to indicate that 
 * editing of this value is
 * complete, the listener can retrieve the value from that
 * <code>Displayable</code> object
 * and then call
 * {@link Display#setCurrentItem(Item)} to return to this item.</p>
 *
 * <a name="keypad"></a>
 * <h2>Keypad Input</h2>
 *
 * <p>The implementation may optionally support delivery of keypad events to
 * the <code>CustomItem</code>.  The implementation indicates
 * the level of support by
 * setting the <code>KEY_PRESS</code>, <code>KEY_RELEASE</code>, and
 * <code>KEY_REPEAT</code> bits in the value
 * returned by <code>getInteractionModes</code>.  
 * Events corresponding to these bits are
 * delivered through calls to the <code>keyPressed()</code>,
 * <code>keyReleased()</code>, and
 * <code>keyRepeated()</code> methods, respectively.  
 * If an implementation supports
 * <code>KEY_RELEASE</code> events, it must also support 
 * <code>KEY_PRESS</code> events.  If an
 * implementation supports <code>KEY_REPEAT</code> events, it must also 
 * support <code>KEY_PRESS</code>
 * and <code>KEY_RELEASE</code> events.  If supported, 
 * <code>KEY_RELEASE</code> events will generally
 * occur after a corresponding <code>KEY_PRESS</code> event is 
 * received, and <code>KEY_REPEAT</code>
 * events will generally occur between <code>KEY_PRESS</code> and 
 * <code>KEY_RELEASE</code> events.
 * However, it is possible for the <code>CustomItem</code> to receive
 * <code>KEY_RELEASE</code> or
 * <code>KEY_REPEAT</code> events without a corresponding 
 * <code>KEY_PRESS</code> if a key is down when
 * the <code>CustomItem</code> becomes visible.</p>
 *
 * <p>Key event methods are passed the <code>keyCode</code> 
 * indicating the key on which the
 * event occurred.  Implementations must provide means for the user to
 * generate events with key codes <code>Canvas.KEY_NUM0</code> 
 * through <code>Canvas.KEY_NUM9</code>,
 * <code>Canvas.KEY_STAR</code>, and <code>Canvas.KEY_POUND</code>.
 * Implementations may also deliver
 * key events for other keys, include device-specific keys. 
 * The set of keys
 * available to a <code>CustomItem</code> may differ depending
 * upon whether commands have been added to it.</p>
 *
 * <p>The application may map key codes to game actions through use of the
 * <code>getGameAction</code> method.  
 * If the implementation supports key events on
 * <code>CustomItems</code>, the implementation must provide a 
 * sufficient set of key codes
 * and a mapping to game actions such that all game actions are available to
 * <code>CustomItems</code>.</p>
 *
 * <p>The set of keys and the key events available to a 
 * <code>CustomItem</code> may differ
 * from what is available on a <code>Canvas</code>.  
 * In particular, on a system that
 * supports traversal, the system might use directional keys for traversal and
 * elect not to deliver these keys to <code>CustomItems</code>. 
 * The mapping between key
 * codes and game actions in a <code>CustomItem</code> may differ
 * from the mapping in a <code>Canvas</code>.  See
 * <a href="Canvas.html#keyevents">Key Events</a>
 * and
 * <a href="Canvas.html#gameactions">Game Actions</a>
 * on class <code>Canvas</code> for further information about key codes and game
 * actions.</p>
 *
 * <a name="pointer"></a>
 * <h2>Pointer Input</h2>
 *
 * <p>The implementation may optionally support delivery of pointer events
 * (such as taps with a stylus) to the <code>CustomItem</code>.  
 * The implementation
 * indicates the level of support by setting the <code>POINTER_PRESS</code>,
 * <code>POINTER_RELEASE</code>, and <code>POINTER_DRAG</code> bits
 * in the value returned by <code>getInteractionModes</code>. 
 * Events corresponding to these bits are delivered
 * through calls to the <code>pointerPressed()</code>, 
 * <code>pointerReleased()</code>, and
 * <code>pointerDragged()</code> methods, respectively.  
 * If an implementation supports
 * <code>POINTER_RELEASE</code> events, it must also support 
 * <code>POINTER_PRESS</code> events.  If an
 * implementation supports <code>POINTER_DRAG</code> events, 
 * it must also support
 * <code>POINTER_PRESS</code> and <code>POINTER_RELEASE</code> events.  
 * If supported, <code>POINTER_RELEASE</code>
 * events will generally occur after a corresponding 
 * <code>POINTER_PRESS</code> event is
 * received, and <code>POINTER_DRAG</code> events will generally occur between
 * <code>POINTER_PRESS</code> and <code>POINTER_RELEASE</code> events.  
 * However, it is possible for the
 * <code>CustomItem</code> to receive <code>POINTER_RELEASE</code> 
 * or <code>POINTER_DRAG</code> events without a
 * corresponding <code>POINTER_PRESS</code> if the pointer is 
 * down when the <code>CustomItem</code> becomes visible.</p>
 *
 * <p>The <code>(x,y)</code> location of the pointer event is 
 * reported with every pointer
 * event.  This location is expressed in the coordinate system of the
 * <code>CustomItem</code>, where <code>(0,0)</code> is the upper-left
 * corner of the <code>CustomItem</code>.  Under
 * certain circumstances, pointer events may occur outside the bounds of the
 * item. </p>
 *
 * <h2>Traversal</h2>
 *
 * <p>An implementation may support traversal <em>internal</em> to a
 * <code>CustomItem</code>, that is, the implementation 
 * may temporarily delegate the
 * responsibility for traversal to the item itself.  Even if there is only one
 * traversal location inside the <code>CustomItem</code>, 
 * the item may want support the
 * internal traversal protocol so that it can perform specialized
 * highlighting, animation, etc. when the user has traversed into it.</p>
 *
 * <p>The implementation indicates its support for traversal internal to a
 * <code>CustomItem</code> by setting one or both of the 
 * <code>TRAVERSE_HORIZONTAL</code> or
 * <code>TRAVERSE_VERTICAL</code> bits in the value returned by
 * <code>getInteractionModes()</code>. If
 * neither of these bits is set, the implementation is unwilling to let
 * <code>CustomItems</code> traverse internally, or the 
 * implementation does not support
 * traversal at all.  If the implementation does support traversal but has
 * declined to permit traversal internal to <code>CustomItems</code>,
 * the implementation
 * will supply its own highlighting outside the 
 * <code>CustomItem's</code> content area.</p>
 *
 * <p>The <code>CustomItem</code> need not support internal
 * traversal at all.  It can do
 * this by returning <code>false</code> to the initial call to the
 * <code>traverse</code> method.  (This is the default behavior if this method
 * hasn't been overridden by the <code>CustomItem</code>.) 
 * If this occurs, the system must
 * arrange for the user to be able to traverse onto and past this item.  The
 * system must also arrange for proper scrolling to take place, particularly
 * if the item exceeds the height of the screen, regardless of whether
 * internal traversal is occurring.</p>
 *
 * <p>An implementation may provide support for delivering keypad or pointer
 * events to <code>CustomItems</code> even if it has declined
 * to support delivering traverse events to <code>CustomItems</code>.  
 * If an implementation provides support for
 * delivering keypad or pointer events to <code>CustomItems</code>,
 * it must provide a means
 * to do so for every <code>CustomItem</code>, even for those
 * that have refused internal
 * traversal by returning <code>false</code> to the initial 
 * <code>traverse()</code> call.  
 * This implies that such implementations must still support some notion
 * of focus for an item, even if that item is not supporting internal
 * traversal.</p>
 *
 * <p>See the documentation for the
 * {@link #traverse traverse} method for a full
 * specification of the behavior and responsibilities required for the item to
 * perform internal traversal.</p>
 *