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showLeft(leftBar()); document.getElementById("ToggleLeft").style.display="inline"; } </script> </head><body onload="load()"> <div id=TopBar> <div id=TopBar_tr> <div id=TopBar_tl> <div id=TopBar_br> <div id=TopBar_bl> <div id=TopBar_right> <a target="_blank" href="http://java.sun.com/javase/6/download.jsp">Download the JDK</a> <br> <a href="../../search.html" target="_blank">Search the Tutorials</a> <br> <a href="javascript:toggleLeft()" id="ToggleLeft">Hide the TOC</a> </div> </div> </div> </div> </div> </div> <div class=PrintHeaders> <b>Trail:</b> Creating a GUI with JFC/Swing <br><b>Lesson:</b> Writing Event Listeners <br><b>Section:</b> Implementing Listeners for Commonly Handled Events </div> <div id=LeftBar class=LeftBar_shown> <div id=Contents> <div class="linkLESSON"><a href="index.html">Writing Event Listeners</a></div><div class="linkAHEAD"><a href="intro.html">Introduction to Event Listeners</a></div><div class="linkAHEAD"><a href="generalrules.html">General Information about Writing Event Listeners</a></div><div class="linkAHEAD"><a href="eventsandcomponents.html">Listeners Supported by Swing Components</a></div><div class="linkAHEAD"><a href="handling.html">Implementing Listeners for Commonly Handled Events</a></div><div class="linkBHEAD"><a href="actionlistener.html">How to Write an Action Listener</a></div><div class="linkBHEAD"><a href="caretlistener.html">How to Write a Caret Listener</a></div><div class="linkBHEAD"><a href="changelistener.html">How to Write a Change Listener</a></div><div class="linkBHEAD"><a href="componentlistener.html">How to Write a Component Listener</a></div><div class="linkBHEAD"><a href="containerlistener.html">How to Write a Container Listener</a></div><div class="linkBHEAD"><a href="documentlistener.html">How to Write a Document Listener</a></div><div class="linkBHEAD"><a href="focuslistener.html">How to Write a Focus Listener</a></div><div class="linkBHEAD"><a href="internalframelistener.html">How to Write an Internal Frame Listener</a></div><div class="nolinkBHEAD">How to Write an Item Listener</div><div class="linkBHEAD"><a href="keylistener.html">How to Write a Key Listener</a></div><div class="linkBHEAD"><a href="listdatalistener.html">How to Write a List Data Listener</a></div><div class="linkBHEAD"><a href="listselectionlistener.html">How to Write a List Selection Listener</a></div><div class="linkBHEAD"><a href="mouselistener.html">How to Write a Mouse Listener</a></div><div class="linkBHEAD"><a href="mousemotionlistener.html">How to Write a Mouse-Motion Listener</a></div><div class="linkBHEAD"><a href="mousewheellistener.html">How to Write a Mouse-Wheel Listener</a></div><div class="linkBHEAD"><a href="propertychangelistener.html">How to Write a Property Change Listener</a></div><div class="linkBHEAD"><a href="tablemodellistener.html">How to Write a Table Model Listener</a></div><div class="linkBHEAD"><a href="treeexpansionlistener.html">How to Write a Tree Expansion Listener</a></div><div class="linkBHEAD"><a href="treemodellistener.html">How to Write a Tree Model Listener</a></div><div class="linkBHEAD"><a href="treeselectionlistener.html">How to Write a Tree Selection Listener</a></div><div class="linkBHEAD"><a href="treewillexpandlistener.html">How to Write a Tree-Will-Expand Listener</a></div><div class="linkBHEAD"><a href="undoableeditlistener.html">How to Write an Undoable Edit Listener</a></div><div class="linkBHEAD"><a href="windowlistener.html">How to Write Window Listeners</a></div><div class="linkAHEAD"><a href="api.html">Listener API Table</a></div><div class="linkAHEAD"><a href="problems.html">Solving Common Event-Handling Problems</a></div></div> </div> <div id=MainFlow class=MainFlow_indented> <span id=BreadCrumbs> <a href=../../index.html target=_top>Home Page</a> > <a href=../index.html target=_top>Creating a GUI with JFC/Swing</a> > <a href=index.html target=_top>Writing Event Listeners</a> </span> <div class=NavBit> <a target=_top href=internalframelistener.html>« Previous</a> • <a target=_top href=../TOC.html>Trail</a> • <a target=_top href=keylistener.html>Next »</a> </div> <div id=PageTitle>How to Write an Item Listener</div> <blockquote>Item events are firedby components that implement the<a class="APILink" target="_blank" href="http://java.sun.com/javase/6/docs/api/java/awt/ItemSelectable.html"><code>ItemSelectable</code></a> interface.Generally, <code>ItemSelectable</code> components maintain on/off state for one or more items.The Swing components that fire item events include<a class="TutorialLink" target="_top" href="../components/button.html#checkbox">check boxes</a>,<a class="TutorialLink" target="_top" href="../components/menu.html">check box menu items</a>, and<a class="TutorialLink" target="_top" href="../components/combobox.html">combo boxes</a>.<p>Here is some item-event handling code taken from<a class="SourceLink" target="_blank" href="examples/ComponentEventDemo.java"><code>ComponentEventDemo.java</code></a>:<blockquote><pre><em>//where initialization occurs</em>checkbox.addItemListener(this);...public void itemStateChanged(ItemEvent e) { if (e.getStateChange() == ItemEvent.SELECTED) { label.setVisible(true); ... } else { label.setVisible(false); }}</pre></blockquote></blockquote><h3><a name="api">The Item Listener API</a></h3><blockquote><p align=center><a name="itemlistener">The ItemListener Interface</a><p><em>Because <code>ItemListener</code> has only one method, it has no corresponding adapter class.</em><table border=1><tr><th align=left>Method</th><th align=left>Purpose</th></tr><tr><td><a class="APILink" target="_blank" href="http://java.sun.com/javase/6/docs/api/java/awt/event/ItemListener.html#itemStateChanged(java.awt.event.ItemEvent)">itemStateChanged(ItemEvent)</a></td><td> Called just after a state change in the listened-to component.</td></tr></table><p align=center><a name="itemevent">The ItemEvent Class</a><p><table border=1><tr><th align=left>Method</th><th align=left>Purpose</th></tr><tr><td><a class="APILink" target="_blank" href="http://java.sun.com/javase/6/docs/api/java/awt/event/ItemEvent.html#getItem()">Object getItem()</a></td><td>Returns the component-specific object associated with the item whose state changed. Often this is a <code>String</code> containing the text on the selected item.</td></tr><tr><td><a class="APILink" target="_blank" href="http://java.sun.com/javase/6/docs/api/java/awt/event/ItemEvent.html#getItemSelectable()">ItemSelectable getItemSelectable()</a></td><td>Returns the component that fired the item event. You can use this instead of the <code>getSource</code> method.</td></tr><tr><td><a class="APILink" target="_blank" href="http://java.sun.com/javase/6/docs/api/java/awt/event/ItemEvent.html#getStateChange()">int getStateChange()</a></td><td>Returns the new state of the item. The <code>ItemEvent</code> class defines two states: <code>SELECTED</code> and <code>DESELECTED</code>.</td></tr></table></blockquote><a name="eg"><h3>Examples that Use Item Listeners</h3></a><blockquote>The following table lists some examples that use item listeners.<p><table><tr><th align=left> Example</th><th align=left> Where Described</th><th align=left> Notes</th></tr><tr valign=top><td> <a href="examples/index.html#ComponentEventDemo"><code>ComponentEventDemo</code></a></td><td> This section and <a href="componentlistener.html">How to Write a Component Listener</a></td><td> Listens for item events on a check box, which determines whether a lable is visible.</td></tr><tr valign=top><td> <a href="../components/examples/index.html#CheckBoxDemo"><code>CheckBoxDemo</code></a></td><td> <a class="TutorialLink" target="_top" href="../components/button.html#checkbox">How to Use Check Boxes</a></td><td> Four check boxes share one item listener, which uses <code>getItemSelected</code> to determine which check box fired the event.</td></tr><tr valign=top><td> <a href="../components/examples/index.html#MenuDemo"><code>MenuDemo</code></a></td><td> <a class="TutorialLink" target="_top" href="../components/menu.html">How to Use Menus</a></td><td> Listens for item events on a check box menu item.</td></tr><tr valign=top><td> <a href="../components/examples/index.html#ScrollDemo"><code>MenuDemo</code></a></td><td> <a class="TutorialLink" target="_top" href="../components/scrollpane.html">How to Use Scroll Panes</a></td><td> Listens for item events on a toggle button.</td></tr></table> </blockquote> <div class=NavBit> <a target=_top href=internalframelistener.html>« Previous</a> • <a target=_top href=../TOC.html>Trail</a> • <a target=_top href=keylistener.html>Next »</a> </div> </div> <div id=Footer><div id=TagNotes> Problems with the examples? Try <a target="_blank" href=../../information/run-examples.html>Compiling and Running the Examples: FAQs</a>. <br> Complaints? Compliments? Suggestions? <a target="_blank" href="http://developer.sun.com/contact/tutorial_feedback.jsp">Give us your feedback</a>.<br><br> <a target="_blank" href="../../information/copyright.html">Copyright</a> 1995-2006 Sun Microsystems, Inc. All rights reserved. <span id=Download></span></div> </div> <div class=PrintHeaders> <b>Previous page:</b> How to Write an Internal Frame Listener <br><b>Next page:</b> How to Write a Key Listener </div> </body></html> ⌨️ 快捷键说明
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