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<h1>Providing Add Connection Functionality</h1>
<p>In a previous chapter it was explained how an <a href="add-feature.htm">add feature</a>
is used to create graphical representations (in this case shapes with rectangles)
for existing business-objects (EClasses). </p>
<p>In this chapter the same functionality shall be provided for connections. Concretely,
an add feature for connections shall be implemented, which creates graphical representations
(connections with polylines) for existing business objects (EReferences).</p>
<p>An add connection feature has to implement the interface
<a href="../../../javadoc/org/eclipse/graphiti/features/IAddFeature.html">IAddFeature</a>.
Instead of implementing it directly it should extend one of the available base classes.
In this example we extend the base class
<a href="../../../javadoc/org/eclipse/graphiti/features/impl/AbstractAddFeature.html">
AbstractAddFeature</a>.</p>
<p>In this case we have to implement/overwrite two methods:</p>
<ul>
<li>The method
<a href="../../../javadoc/org/eclipse/graphiti/func/IAdd.html#canAdd(org.eclipse.graphiti.features.context.IAddContext)">canAdd</a> has to check the given context and therefore it decides if a business
object can be added.</li>
<li>The method
<a href="../../../javadoc/org/eclipse/graphiti/func/IAdd.html#add(org.eclipse.graphiti.features.context.IAddContext)">add</a> finally has to create the pictogram element (connection) and has to establish
the linkage to the business object. Additionally we have to create the graphics
algorithm (polyline). </li>
</ul>
<p>You can see the complete implementation of the add connection feature here:</p>
<div class="literallayout">
<div class="incode">
<p class="code"><span class="keyword">package </span>org.eclipse.graphiti.examples.tutorial.features;<br>&nbsp;<br>
<span class="keyword">public class</span> TutorialAddEReferenceFeature
<span class="keyword">extends </span>AbstractAddFeature {<br>&nbsp;<br>&nbsp;&nbsp;&nbsp;
<span class="keyword">public </span>TutorialAddEReferenceFeature (IFeatureProvider
fp) {<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
<span class="keyword">super</span>(fp);<br>&nbsp;&nbsp;&nbsp; }<br>&nbsp;<br>&nbsp;&nbsp;&nbsp;
<span class="keyword">public </span>PictogramElement add(IAddContext context)
{<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; IAddConnectionContext addConContext
= (IAddConnectionContext) context;<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
EReference addedEReference = (EReference) context.getNewObject();<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
IPeCreateService peCreateService = Graphiti.getPeCreateService();<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <span class="comment">//
CONNECTION WITH POLYLINE</span><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
Connection connection = peCreateService<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
.createFreeFormConnection(getDiagram());<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
connection.setStart(addConContext.getSourceAnchor());<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
connection.setEnd(addConContext.getTargetAnchor());<br>&nbsp;<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
IGaService gaService = Graphiti.getGaService();<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
Polyline polyline = gaService.createPolyline(connection);<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
polyline.setLineWidth(2);<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
polyline.setForeground(manageColor(IColorConstant.<span class="string"><em>BLACK</em></span>));<br>&nbsp;<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
<span class="comment">// create link and wire it</span><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
link(connection, addedEReference);<br>&nbsp;<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
<span class="keyword">return </span>connection;<br>&nbsp;&nbsp;&nbsp; }<br>&nbsp;<br>&nbsp;&nbsp;
<span class="keyword">&nbsp;public boolean</span> canAdd(IAddContext context)
{<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <span class="comment">//
return true if given business object is an EReference<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
// note, that the context must be an instance of IAddConnectionContext</span><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
<span class="keyword">if</span> (context <span class="keyword">instanceof
</span>IAddConnectionContext<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
&amp;&amp; context.getNewObject() <span class="keyword">instanceof </span>EReference)
{<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
<span class="keyword">return true</span>;<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
}<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <span class="keyword">&nbsp;return
false</span>;<br>&nbsp;&nbsp;&nbsp; }<br>}<br></p>
</div>
</div>
<p>&nbsp;</p>
<p>Additionally the feature provider has to deliver our newly created feature (overwrite
the method
<a href="../../../javadoc/org/eclipse/graphiti/features/IFeatureProvider.html#getAddFeature(org.eclipse.graphiti.features.context.IAddContext)">
getAdd</a>).</p>
<p>This implementation can be seen here:</p>
<p>&nbsp;</p>
<div class="literallayout">
<div class="incode">
<p class="code">@Override<br><span class="keyword">public </span>IAddFeature
getAddFeature(IAddContext context) {<br>&nbsp;&nbsp;&nbsp;
<span class="comment">// is object for add request a EClass or EReference?</span><br>&nbsp;&nbsp;&nbsp;
<span class="keyword">if </span>(context.getNewObject()
<span class="keyword">instanceof </span>EClass) {<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
<span class="keyword">return new</span> TutorialAddEClassFeature(<span class="keyword">this</span>);<br>&nbsp;&nbsp;&nbsp;
} <span class="keyword">else if</span> (context.getNewObject()
<span class="keyword">instanceof </span>EReference) {<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
<span class="keyword">return new</span> TutorialAddEReferenceFeature(<span class="keyword">this</span>);<br>&nbsp;&nbsp;&nbsp;
}<br>&nbsp;&nbsp;&nbsp; <span class="keyword">return super</span>.getAddFeature(context);<br>
} </p>
</div>
</div>
<p>&nbsp;</p>
<p>Before this new add connection feature can be tested, we have to
<a href="create-connection-feature.htm">provide create connection functionality</a>
as described in the next chapter.</p>
<p>&nbsp;</p>
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