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        <h1>NetBeans Selection Management Tutorial II&#8212;Using Nodes</h1>

        <p>The <a href="nbm-selection-1.html">previous tutorial</a> covered the basics
            of component-wide selection handling in NetBeans&#8212;how to provide objects from
            a <code><a href="http://wiki.netbeans.org/wiki/view/DevFaqWindowsTopComponent">TopComponent</a></code>'s
            <code><a href="http://wiki.netbeans.org/wiki/view/DevFaqLookup">Lookup</a></code>, and
            how to write other components that are sensitive to the <code>Lookup</code> of whatever
            component has focus.</p>

        <p>This tutorial focuses on the <a href="https://netbeans.org/download/dev/javadoc/org-openide-nodes/overview-summary.html">Nodes API</a>, which makes it possible to do more granular
            views and selection than just component-level selection.  Of course, you could write
            a component that reads and writes into its own Lookup whatever it wants, and 
            provides more granular selection logic that way.  But the Nodes API makes it very
            easy to do this, and offers a number of advantages over doing it yourself.</p>

        <p><strong class="notes">Note: </strong>This document uses NetBeans Platform 7.3 and
            NetBeans IDE 7.3. If you
            are using an earlier version, see <a href="72/nbm-selection-2.html">the previous version
                of this document</a>.</p>

        <p><b>Contents</b></p>
        <p><img src="../images/articles/73/netbeans-stamp.png" class="stamp" width="114" height="114" alt="Content on this page applies to NetBeans IDE 7.3" title="Content on this page applies to NetBeans IDE 7.3"/></p>
        <ul class="toc">
            <li><a href="#intro">Introduction to the Nodes API</a></li>
            <li><a href="#explorer">Creating an Explorer View</a></li>
            <li><a href="#nodes-and-children">Implementing Nodes and Node Children</a></li>
            <li><a href="#running">Running the Tutorial</a></li>
            <li><a href="#exploring">Exploring Explorer</a></li>
            <li><a href="#handling">Handling Multi-Selection</a></li>
            <li><a href="#review">Review of Concepts</a></li>
            <li><a href="#next">Next Steps</a></li>
        </ul>

        <p><b>To follow this tutorial, you need the software and resources listed in the following 
                table.</b></p>

        <table>
            <tbody>
                <tr>
                    <th class="tblheader" scope="col">Software or Resource</th>
                    <th class="tblheader" scope="col">Version Required</th>
                </tr>
                <tr>
                    <td class="tbltd1"><a href="https://netbeans.org/downloads/index.html">NetBeans IDE</a></td>
                    <td class="tbltd1">version 7.3 or above</td>
                </tr>
                <tr>
                    <td class="tbltd1"><a href="http://java.sun.com/javase/downloads/index.jsp">Java Developer Kit (JDK)</a></td>
                    <td class="tbltd1">version 6 or above</td>
                </tr>
            </tbody>
        </table>

        <p class="tips">For troubleshooting purposes, you are welcome to download the <a href="http://java.net/projects/nb-api-samples/sources/api-samples/show/versions/7.3/tutorials/selection-management/2-of-4/EventManager">completed tutorial source code</a>.</p>

        <h2 class="tutorial"><a name="intro"></a>Introduction to the Nodes API</h2>

        <p>The first advantage is that the Nodes API provides a <i>presentation layer</i>&#8212;a 
            layer between the data model being edited in some way, and the UI components
            that expose the data model to the user.  This is quite useful and powerful, as
            the same model may be presented in multiple ways, or with multiple UIs.</p>

        <p>The second advantage is the Explorer API&#8212;the module <code>org.openide.explorer</code>
            provides a vast array of components&#8212;trees, lists, tree tables and more&#8212;which can
            render a Node and its children.</p>

        <p>A <code>Node</code> is a generic hierarchical object&#8212;a <code>Node</code> has:</p>

        <ul>
            <li>Children&#8212;Nodes in a hierarchy underneath it, that can be displayed in a tree</li>
            <li>Actions&#8212;An array of actions that can be displayed in a popup menu</li>
            <li>Display Name&#8212;A human-readable, localized display name that can be shown in a UI component</li>
            <li>Icon&#8212;An icon that can be shown in a UI component</li>
        </ul>

        <p>and <code>Node</code>s can fire changes in any of the above, and the explorer UI components
            will automatically update themselves.</p>

        <p>This is <i>not</i> to say that the content of the previous tutorial was useless&#8212;on 
            the contrary, it is the reason the Nodes API can work.  The reason:  
            <code>org.openide.nodes.Node</code> has a method, you guessed it, <code>getLookup()</code>.
            In fact what is happening when you change selection in the Projects tab in the IDE,
            for example, is...the Projects tab is a TopComponent.  It proxies the <code>Lookup</code>
            of whatever object(s) are currently selected in the tree&#8212;just as the
            <code>Utilities.actionsGlobalContext()</code> <code>Lookup</code> proxies whichever
            component is focused and fires changes when focus changes.</p>

        <p>Thanks to the components in the Explorer API, it is very easy to create your own
            views of a tree of <code>Node</code>s, and have this type of proxying in your
            own components with very little code.  Viewer type components such as the 
            <code>MyViewer</code> component in the previous tutorial do not have to do anything
            special to be able to respond to selection changes in Explorer components&#8212;they
            will automatically be notified as selection changes.</p>

        <h2 class="tutorial"><a name="explorer"></a>Creating an Explorer View</h2>
        <p>The first thing you will do is some substantial modifications to your
            <code>MyEditor</code> editor component.  This starts with opening it in the
            editor.</p>

        <div class="indent">

            <ol>
                <li><p>First, bring up the properties dialog for the My Editor project by right-clicking
                        the My Editor project and choosing Properties.
                        On the Libraries tab, click the Add Dependency button, and type &quot;BeanTreeView&quot;
                        in the dialog:</p>  
                    <p><img src="../images/tutorials/selection-2/73/add-dep-1.png"/></p>
                    <p>Click OK once you see the Explorer & Property Sheet API listed,
                        as shown above. This will add a dependency on the Explorer API module,
                        so you can use classes from it.</p>
                </li>

                <li>Switch to the form designer, select all of the components, and 
                    delete them. In the next steps, we will use a component from
                    the Explorer & Property Sheet API, instead of the text fields and
                    button we
                    have been using so far.</li>

                <li><p>Rewrite the constructor of the <tt>MyEditor</tt> class as shown below:</p>

                    <pre class=examplecode>public MyEditor() {

    initComponents();
    Event obj = new Event();
    associateLookup(new AbstractLookup(content));

    <b>setLayout(new BorderLayout());
    add(new BeanTreeView(), BorderLayout.CENTER);</b>

    setDisplayName("MyEditor " + obj.getIndex());

}</pre>
                    <p><code>BeanTreeView</code>
                        is a component from the Explorer & Property Sheet API&#8212;a basic <code>JTree</code>-based
                        view over a <code>Node</code> and its children, with built-in handling
                        of popup menus, searching and more. Press Ctrl-Shift-I to import BeanTreeView, because
                        the import statement needs to be added.</p></li>

                <li>The next step is to give your tree something to show.  Explorer UI
                    components work like this:  When added to a container, they search that
                    container and their ancestors until they find one that implements 
                    <code>ExplorerManager.Provider</code>.  So you don't set the node to be viewed directly
                    on the component&#8212;you set it on the component's manager.  This makes
                    it possible to have multiple views, master/detail views and such, all
                    managed by a single manager.  Add to the signature of MyEditor as follows:
                    <pre class=examplecode>
public class MyEditor extends TopComponent <b>implements ExplorerManager.Provider</b> {</pre>
                    Then press Ctrl-Shift-I to fix imports.  Keeping the caret in the signature
                    line, a lightbulb glyph should appear in the margin.  Press Alt-Enter, and
                    accept the hint &quot;Implement all abstract methods&quot;.  This will add one
                    method, <code>getExplorerManager()</code>.  Implement it as follows:
                    <pre class=examplecode>private final ExplorerManager mgr = new ExplorerManager();

public ExplorerManager getExplorerManager() {
    return mgr;
}</pre>
                </li>

                <li>Now, since the goal is one component that can display multiple
                    <code>Event</code>s, you need a <code>Node</code> or two to display in your component.
                    Each one will own its own instance of <code>Event</code>.  So,
                    right now you'll just add the code that will create a root node for
                    your tree view.  Add the following line to the constructor:
                    <pre class=examplecode>
mgr.setRootContext(new AbstractNode(Children.create(new EventChildFactory(), true)));</pre>
                    This is the code that sets the root node for all of the explorer views
                    that are child components of <code>MyEditor</code>. The <code>Children.create</code>
                    is a static call from the NetBeans APIs that
                    will, thanks to the <code>true</code> parameter, create the child components
                    asynchronously, that is, as needed, instead of all at once.
                </li>
                <li>If you tried Fix Imports, you may have seen the error dialog telling
                    you that neither <code>AbstractNode</code>, <code>Children</code>, nor <code>EventChildFactory</code>
                    could be resolved.  To resolve <code>AbstractNode</code> and <code>Children</code>, you need to add
                    one dependency, on the Nodes API module.  Right click the My Editor project,
                    go to the Libraries page and click Add Dependency.  Type &quot;AbstractNode&quot; in
                    the Add dialog, and when the item &quot;Nodes API&quot; in the list is
                    selected, click OK or press Enter.</li>

                <li>Now, back in the source editor, press Ctrl-Shift-I to Fix Imports.  You
                    will be notified that <code>EventChildFactory</code> could not be resolved.  That's
                    okay&#8212;you're about to write it, in the next section.</li>
            </ol>

        </div>

        <h2 class="tutorial"><a name="nodes-and-children"></a>Implementing Nodes and Node Children</h2>
        <p>You'll notice you're using a class called <code>AbstractNode</code> above.  Despite
            its name, it is not an abstract class!  It is a utility implementation of 
            <code>org.openide.nodes.Node</code> which can save you some time and trouble&#8212;rather
            than implement Node yourself, you can just create an AbstractNode and pass it a 
            <code>Children</code> object which will provide child nodes for it, and then set
            its icon and display name as needed.  So it is a simple way to get a <code>Node</code>
            object to represent something, without needing to do any subclassing of <code>Node</code>
            itself.</p>

        <p>The next step is to implement <code>EventChildFactory</code>, so that there are subnodes
            underneath the initial node.</p>

        <div class="indent">

            <ol>
                <li>Right click the <code>org.myorg.myeditor</code> package in the My Editor 
                    project, and choose New &gt; Java Class from the popup menu.
                    In the New Java Class wizard, name the class &quot;EventChildFactory&quot;, and click
                    Finish or press Enter to create the class.</li>

                <li>Modify the signature of the class so it extends <code>ChildFactory</code>:
                    <pre class=examplecode>
class EventChildFactory extends ChildFactory&lt;Event&gt; {</pre>
                    <p>Press Ctrl-Shift-I to Fix Imports.</p></li>
                <li>Position the caret in the class signature line.  When the lightbulb glyph appears
                    in the margin, press Alt-Enter and then Enter again to accept the hint &quot;Implement
                    all Abstract Methods&quot;.  This will add a <code>createKeys(List&lt;Event&gt; toPopulate)</code>
                    method&#8212;this is where you will create the keys, on a background thread, that will be used to
                    create the children of your root
                    node.</li>
                <li>But first, you want to override one method&#8212;<code>createKeys</code>. 
                    <code>ChildrenFactory.createKeys</code>
                    is called the first time something pays attention to this Children object&#8212;the first
                    time it is asked for its child nodes.  So you can delay creation of child Nodes until
                    the user has really expanded the parent node in a view and needs to see them.
                    Implement the method as follows:
                    <pre class=examplecode>
@Override
protected boolean createKeys(List<Event> toPopulate) {
    Event[] objs = new Event[5];
    for (int i = 0; i < objs.length; i++) {
        objs[i] = new Event();
    }
    toPopulate.addAll(Arrays.asList(objs));
    return true;
}</pre>
                    As you may have guessed from the name <code>ChildFactory</code>, what your parent
                    class does is take an array or <code>Collection</code> of key objects, and act as a
                    factory for <code>Node</code>s for them. For each element in the array or collection
                    you pass to the <code>toPopulate</code> list above, the <code>createNodeForKey()</code> shown
                    below will be called 
                    once when <code>true</code> is returned (note this means that if you want, you can have more than one node to represent
                    one object).
                </li>
                <li><p>Now you need to implement the code that actually creates Node objects for all
                        of these.  Implement <code>createNodeForKey</code> as follows:
                        <pre class=examplecode>
@Override
protected Node createNodeForKey(Event key) {
    Node result = new AbstractNode(
        Children.create(new EventChildFactory(), true), 
        Lookups.singleton(key));
    result.setDisplayName(key.toString());
    return result;
}</pre>
                    </p>
                    <p>The new <tt>Node</tt> is created by passing in the definition of its
                        <tt>Children</tt>, together with the current <tt>Event</tt>, which
                        is put into the <tt>Lookup</tt> of the <tt>Node</tt>. When the user
                        selects the <tt>Node</tt>, the object in its <tt>Lookup</tt> will be
                        proxied by the <tt>Lookup</tt> of the <tt>TopComponent</tt>, which in
                        turn is proxied by the global <tt>Lookup</tt>.
                        In this way, you make the current <tt>Event</tt> object available to
                        any object that is interested in it, whenever the <tt>Node</tt> is
                        selected. Press Ctrl-Shift-I to Fix Imports.</p></li>
                <li>The last step is to install a bit of plumbing code that will wire up your
                    explorer manager to your TopComponent's lookup.  First, delete the line 
                    <pre class=examplecode>
private final InstanceContent content = new InstanceContent();</pre>
                    from the head of the class definition&#8212;you will be using a utility to wire
                    up the selected <code>Node</code>'s <code>Lookup</code> to your component's
                    <code>Lookup</code>.
                </li>
                <li>Modify the constructor of <code>MyEditor</code> so it looks like this:
                    <pre class=examplecode>public MyEditor() {

    initComponents();
    Event obj = new Event();
    <b>associateLookup(ExplorerUtils.createLookup(mgr, getActionMap()));</b>

    setLayout(new BorderLayout());
    add(new BeanTreeView(), BorderLayout.CENTER);

    setDisplayName("MyEditor " + obj.getIndex());

    mgr.setRootContext(new AbstractNode(Children.create(new EventChildFactory(), true)));

}</pre>
                </li>

            </ol>

        </div>

        <h2 class="tutorial"><a name="running"></a>Running the Tutorial</h2>
        <p>You may have noticed that because you pass a new instance of <code>EventChildFactory</code>
            to each <code>AbstractNode</code> you create, that you will end up with an infinitely
            deep tree of <code>Events</code>&#8212;each <code>Node</code> will have five child
            <code>Node</code>s, each with its own <code>Event</code>.</p>
        <p>
            You are now ready to run, so right-click <code>EventManager</code> and choose
            Clean and Build, and then right-click again and choose Run from the popup menu.
            When the application starts, you should be able to browse the <tt>Events</tt>,
            as shown below:</p>
        <p>
            <img src="../images/tutorials/selection-2/73/new-node-1.png"/></p>
        <p>
            Notice that as you click and/or expand different nodes, the viewer and the property sheet update
            themselves
            to show the <code>Event</code> belonging to each node, as shown below:</p>

        <p>
            <img src="../images/tutorials/selection-2/73/new-node-2.png"/>
        </p>

        <h2 class="tutorial"><a name="exploring"></a>Exploring Explorer</h2>
        <p>Now that you have the above code, it can be interesting to explore some of the
            other components available in the Explorer & Property Sheet API,
            which can also render a <code>Node</code>
            and it's children.  You can do this by opening <code>MyEditor</code> in
            the Source view and changing <code>add (new BeanTreeView(), BorderLayout.CENTER)</code>
            to something different, in the constructor.</p>

        <p>Some of the options are:</p>
        <ul>
            <li><b>OutlineView</b>&#8212;a tree-table&#8212;a table whose leftmost column is
                a tree</li>
            <li><b>IconView</b>&#8212;a component that shows Node children in equally spaced
                icons, rather like Windows Explorer</li>
            <li><b>ListView</b>&#8212;display nodes in a JList (you can set how deep into the
                Node hierarchy it should go)</li>
            <li><b>ChoiceView</b>&#8212;a combo-box view of a Node and its children</li>
            <li><b>MenuView</b>&#8212;a <code>JButton</code> that pops up a menu of a Node and
                its children</li>
        </ul>

        <h2 class="tutorial"><a name="handling"></a>Handling Multi-Selection</h2>
        <p>You may have noticed that <code>BeanTreeView</code>, the basic tree view for
            Nodes, lets you select more than one Node at a time.  Therefore, it might be
            desirable to modify your viewer component to display information about all of
            the selected nodes:</p>

        <div class="indent">

            <ol>
                <li>Open <code>org.myorg.myviewer.MyViewerTopComponent</code> from the My Viewer
                    project, in the editor.</li>
                <li>Replace the <code>resultChanged()</code> listener method with the following
                    code:
                    <pre class=examplecode>@Override
public void resultChanged(LookupEvent lookupEvent) {
    Collection&lt;? extends Event&gt; allEvents = result.allInstances();
    if (!allEvents.isEmpty()) {
        StringBuilder text1 = new StringBuilder();
        StringBuilder text2 = new StringBuilder();
        for (Iterator i = allEvents.iterator(); i.hasNext();) {
            Event o = (Event) i.next();
            text1.append(o.getIndex());
            text2.append(o.getDate().toString());
            if (i.hasNext()) {
                text1.append(',');
                text2.append(',');
            }
        }
        jLabel1.setText(text1.toString());
        jLabel2.setText(text2.toString());
    } else {
        jLabel1.setText("[no selection]");
        jLabel2.setText("");
    }
}</pre>
                </li>

            </ol>

        </div>

        <p>So you can see that, not only does the <code>Lookup</code> created by <code>ExplorerUtils</code>
            handle proxying the <code>Lookup</code> of whatever <code>Node</code> is 
            selected;  it also correctly proxies the <code>Lookup</code>s of multiple
            <code>Node</code>s.</p>
        <p>
            <img src="../images/tutorials/selection-2/73/new-node-3.png"/></p>

        <h2 class="tutorial"><a name="review"></a>Review of Concepts</h2>
        To review a few of the concepts you've covered here:

        <ul>
            <li>A <code>Lookup</code> is like a <code>Map</code> where the keys are classes and the values are
                instances of those classes.  It's also useful to think of a <code>Lookup</code>
                as a <i>place</i> that objects swim into and out of, and you can subscribe to
                be notified of the arrival and departure of specific types of object.</li>

            <li><code>Utilities.actionsGlobalContext()</code> is a <code>Lookup</code> which
                proxies the <code>Lookup</code> of whichever <code>TopComponent</code> currently
                has keyboard focus, and fires changes when focus moves to a different component.</li>

            <li><code>Node</code>s are presentation objects that can be displayed in
                a tree, list or other component from the Explorer API.  Each <code>Node</code>
                has its own <code>Lookup</code>.</li>

            <li>Just as <code>Utilities.actionsGlobalContext</code> proxies the <code>Lookup</code>
                of TopComponents (so you can just ask that lookup for a result and listen for changes
                in it, rather than having to track focus changes yourself), so also the <code>Lookup</code>
                created by <code>ExplorerUtils.createLookup(ExplorerManager, ActionMap)</code> will
                create a <code>Lookup</code> which automatically proxies the <code>Lookup</code> of
                whatever <code>Node</code>(s) are selected in an Explorer component.
            </li>
        </ul>

        <!--    
            <p><h2 class="perf"><a name="next"></a>Nodes and Performance/GUI Responsiveness</h2>
            In general, Nodes are lightweight objects, and inexpensive to create.  However,
            sometimes that is not true of the objects they model.  Here are two techniques to
            overcome cases where fetching the data that needs to be displayed causes an 
            unacceptable lag:
        
            <h3 class="perf"><a name="next"></a>Background Initialization</h3>
            If you control the root <code>Node</code>, try something like the following:
            
            <pre></pre>
        -->

        <br>
            <div class="feedback-box"><a href="https://netbeans.org/about/contact_form.html?to=3&amp;subject=Feedback:%20Selection%207.3%20Tutorial%20Part%202">Send Us Your Feedback</a></div>
            <br style="clear:both;" />

            <h2 class="tutorial"><a name="next"></a>Next Steps</h2>
            <p>So you now have a view that can display <code>Node</code>s that expose some
                underlying model object (<code>Event</code> in your case).  In the
                <a href="nbm-nodesapi2.html">next tutorial</a>, you will cover how to enhance
                the Nodes you have already created with actions, properties and more 
                colorful display names.</p>

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