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| <TITLE>Extension points and the registry</TITLE> |
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| <H3> |
| Extension points and the registry</H3> |
| <p> |
| While the "bundle" aspects of a plug-in may be interesting to the runtime plug-in and runtime tools, |
| it is much more common that a plug-in is concerned with what extension points have been defined |
| by plug-ins and what extensions are contributed by plug-ins. This information is provided |
| by the platform extension registry, <b><a href="../reference/api/org/eclipse/core/runtime/IExtensionRegistry.html"> |
| IExtensionRegistry</a></b>. |
| </p> |
| <p>Why might a plug-in want to know what extensions are present? A concrete example will help show |
| the need for this information and the protocol for getting it.</p> |
| <p>Recall the workbench <b>Show View</b> dialog which shows all of the available views that have |
| been installed in the platform.</p> |
| <img src="images/showview.png" alt="Show View dialog with Hello entry" border="0"> |
| <p> |
| We know that the category names and view names of all contributed views are specified in the |
| <b>plugin.xml</b> file for any plug-in that contributes an extension for <b>org.eclipse.ui.views</b>. |
| But how does the workbench find out this information? From the platform extension registry. The following |
| code is a simplified snippet based on the workbench implementation of the <b>Show View</b> dialog: |
| </p> |
| <pre> |
| ... |
| IExtensionRegistry registry = <b>Platform.getExtensionRegistry()</b>; |
| IExtensionPoint point = <b>registry.getExtensionPoint("org.eclipse.ui.views")</b>; |
| if (point == null) return; |
| IExtension[] extensions = <b>point.getExtensions()</b>; |
| for (int i = 0; i < extensions.length; i++) |
| readExtension(extensions[i]); //get the information about each extension |
| ... |
| </pre> |
| <p> |
| We see above that the registry can be obtained from the <b><a href="../reference/api/org/eclipse/core/runtime/Platform.html"> |
| Platform</a></b> class. The protocol in <b><a href="../reference/api/org/eclipse/core/runtime/IExtensionRegistry.html"> |
| IExtensionRegistry</a></b> is used to find the extension point named <b>org.eclipse.ui.views</b>. Information in the registry |
| about particular extension points or extensions can be found using protocol defined in |
| <b><a href="../reference/api/org/eclipse/core/runtime/IExtensionRegistry.html">IExtensionRegistry</a></b>, |
| <b><a href="../reference/api/org/eclipse/core/runtime/IExtensionPoint.html">IExtensionPoint</a></b>, |
| and <b><a href="../reference/api/org/eclipse/core/runtime/IExtension.html">IExtension</a></b>. |
| The javadoc for these classes provides detailed information about the registry protocol. |
| </p> |
| <p> |
| Once the extension definition of interest has been found, protocol in |
| <b><a href="../reference/api/org/eclipse/core/runtime/IConfigurationElement.html">IConfigurationElement</a></b> |
| can be used to examine the individual attributes of an extension. |
| </p> |
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