listcellrenderer.java.svn-base

j2me设计的界面包

/*
 * Copyright 2008 Sun Microsystems, Inc.  All Rights Reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Sun designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Sun in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
 * CA 95054 USA or visit www.sun.com if you need additional information or
 * have any questions.
 */
package com.sun.lwuit.list;

import com.sun.lwuit.Component;
import com.sun.lwuit.List;

/**
 * A "rubber stamp" tool that allows us to extract a component (often the same
 * component instance for all invocations) that is initialized to the value 
 * of the current item extracted from the model, this component is drawn on the
 * list and discarded. No state of the component is kept and the component is
 * essentially discarded.
 * <p>An instance of a renderer can be developed as such:
 * <pre>
<strong>public</strong> <strong>class</strong> <font color="#2040a0">MyYesNoRenderer</font> <strong>extends</strong> <font color="#2040a0">Label</font> <strong>implements</strong> <font color="#2040a0">ListCellRenderer</font> <font color="4444FF"><strong>{</strong></font>
    <strong>public</strong> <font color="#2040a0">Component</font> <font color="#2040a0">getListCellRendererComponent</font><font color="4444FF"><strong>(</strong></font><font color="#2040a0">List</font> <font color="#2040a0">list</font>, <font color="#2040a0">Object</font> <font color="#2040a0">value</font>, <strong>int</strong> <font color="#2040a0">index</font>, <strong>boolean</strong> <font color="#2040a0">isSelected</font><font color="4444FF"><strong>)</strong></font> <font color="4444FF"><strong>{</strong></font>
        <strong>if</strong><font color="4444FF"><strong>(</strong></font> <font color="4444FF"><strong>(</strong></font><font color="4444FF"><strong>(</strong></font><font color="#2040a0">Boolean</font><font color="4444FF"><strong>)</strong></font><font color="#2040a0">value</font><font color="4444FF"><strong>)</strong></font>.<font color="#2040a0">booleanValue</font><font color="4444FF"><strong>(</strong></font><font color="4444FF"><strong>)</strong></font> <font color="4444FF"><strong>)</strong></font> <font color="4444FF"><strong>{</strong></font>
            <font color="#2040a0">setText</font><font color="4444FF"><strong>(</strong></font><font color="#008000">&quot;Yes&quot;</font><font color="4444FF"><strong>)</strong></font><font color="4444FF">;</font>
        <font color="4444FF"><strong>}</strong></font> <strong>else</strong> <font color="4444FF"><strong>{</strong></font>
            <font color="#2040a0">setText</font><font color="4444FF"><strong>(</strong></font><font color="#008000">&quot;No&quot;</font><font color="4444FF"><strong>)</strong></font><font color="4444FF">;</font>
        <font color="4444FF"><strong>}</strong></font>
        <strong>return</strong> <strong>this</strong><font color="4444FF">;</font>
    <font color="4444FF"><strong>}</strong></font>
    <strong>public</strong> <font color="#2040a0">Component</font> <font color="#2040a0">getListFocusComponent</font><font color="4444FF"><strong>(</strong></font><font color="#2040a0">List</font> <font color="#2040a0">list</font><strong>)</strong></font> <font color="4444FF"><strong>{</strong></font>
        <font color="#2040a0">Label label = new label</font><strong>(&quot;&quot;);</strong>
        <font color="#2040a0">label.getStyle().setBgTransparency(</font><font color="#008000">100</font>);
     </strong>
        <strong>return</strong> <font color="#2040a0">label</font><font color="4444FF">;</font>
    <font color="4444FF"><strong>}</strong></font>
<font color="4444FF"><strong>}</strong></font>
 * </pre>
 * 
 * <p>It is recommended that the component whose values are manipulated would not 
 * support features such as repaint(). This is accomplished by overriding repaint
 * in the subclass with an empty implementation. This is advised for performance
 * reasons, otherwise every change made to the component might trigger a repaint that 
 * wouldn't do anything but still cost in terms of processing.
 * 
 * @author Chen Fishbein
 */
public interface ListCellRenderer { 
    
    /**
     * Returns a component instance that is already set to render "value". While it is not a requirement
     * many renderes often derive from a component (such as a label) and return "this".
     * Notice that a null value for the value argument might be sent when refreshing the theme of the
     * list.
     */
    public Component getListCellRendererComponent(List list, Object value, int index, boolean isSelected);
    
    /**
     * Returns a component instance that is painted under the currently focused renderer
     * and is animated to provide smooth scrolling. 
     * When the selection moves, this component is drawn above/bellow the list items - 
     * it is recommended to give this component some level of transparency (see above code example). 
     * This method is optional an implementation 
     * can choose to return null.
     * 
     * @see List#setSmoothScrolling
     */
    public Component getListFocusComponent(List list);
    
}