platform-ui-home/object-aware-contributions/objCont.htm

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-revision 1.1, Wed Dec 10 20:02:40 2003 UTC
+revision 1.2, Fri Jun 11 15:12:05 2004 UTC
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  <body>
  <h1>Content Sensitive Object Contributions</h1>
- <p><em>Last modified December 10, 2003</em></p>
+ <p><em>Last modified June 10, 2004</em></p>
  <p>Context menus for some applications have previously only been able to exclude
    some menu options based on peripheral information known about the resources
    selected (the number of resources selected, the physical name of the file, the
    type of the resource, etc.). There are some cases where a restricted amount
-   of information, known about the contents of the resource would significantly
+   of information known about the contents of the resource would significantly
-   reduce unusable options from the menus. The first area targeted is that of XML
+   reduce unusable options from the menus. Consider XML files as a good example
-   files. There are numerous situations where an action is applicable for one type
+   of where such information would be useful. There are numerous situations where
-   of XML file but not another. For example, some XML files contain Ant scripts.
+   an action is applicable for one type of XML file but not another. For example,
-   The action &quot;Run Ant...&quot; makes sense in its context menu. But this
+   some XML files contain Ant scripts. The action &quot;Run Ant...&quot; makes
-   action is not applicable to an XML file used to define a plug-in.</p>
+   sense in its context menu. But this action is not applicable to an XML file
+   used to define a plug-in.</p>
+ <p>The notion of a content type has been added to Eclipse. A new extension point,
+   org.eclipse.core.runtime.contentTypes allows plug-ins to contribute to the Platform
+   content type catalog. Further, classes called Content Type Describers have been
+   added.</p>
+ <p>Initially, two content describers will be supported: BinarySignatureDescriber
+   and XMLRootElementContentDescriber. Eclipse developers may create their own
+   content describers. The Platform Plug-in Developer Guide (Programmer's Guide
+   -&gt; Runtime overview -&gt; Content types) describes this in more detail.</p>
+ <h3>XMLRootElementContentDescriber</h3>
  <p>It will now be possible to define object contributions which are specific to
-   an XML file with a given top level tag or which specify a given DTD. The objectState
+   an XML file with a given top level tag or which specify a given DTD. To do this,
-   key of an ActionExpression will be used to specify these values as follows:</p>
+   define an extension to the org.eclipse.core.runtime.contentTypes extension point
- <p><font size="3">&lt;objectState name=&quot;xmlFirstTag&quot; value=&quot;<em>tagValue</em>&quot;/&gt;</font></p>
+   with a describer class of XMLRootElementContentDescriber and parameters indicating
- <p><font size="3">&lt;objectState name=&quot;xmlDTDName&quot; value=&quot;<em>dtdValue</em>&quot;\&gt;</font></p>
+   the top level tag name or the dtd name as follows:</p>
+ <pre>   &lt;extension
+        point=&quot;org.eclipse.core.runtime.contentTypes&quot;&gt;
+        &lt;content-type
+            id=&lt;id&gt;
+            name=&lt;name&gt;
+            base-type=&quot;org.eclipse.core.runtime.xml&quot;&gt;
+            &lt;describer class=&quot;org.eclipse.core.runtime.content.XMLRootElementContentDescriber&quot;&gt;
+                &lt;parameter name=&quot;element&quot; value=<em>tagValue</em> /&gt;
+            &lt;/describer&gt;
+        &lt;/content-type&gt;
+    &lt;/extension&gt;</pre>
+ or
+ <pre>   &lt;extension
+        point=&quot;org.eclipse.core.runtime.contentTypes&quot;&gt;
+        &lt;content-type
+            id=&lt;id&gt;
+            name=&lt;name&gt;
+            base-type=&quot;org.eclipse.core.runtime.xml&quot;&gt;
+            &lt;describer class=&quot;org.eclipse.core.runtime.content.XMLRootElementContentDescriber&quot;&gt;
+                &lt;parameter name=&quot;dtd&quot; value=<em>dtdValue</em> /&gt;
+            &lt;/describer&gt;
+        &lt;/content-type&gt;
+     &lt;/extension&gt;</pre>
  <blockquote>
    <p><font size="3">where <em>tagValue</em> represents the name of the top level
      tag to match and</font></p>
-Line 30
+Line 64
      the XML file.</font></p>
  </blockquote>
  <p><font size="3">Consider the following object contribution in a plugin.xml file:</font></p>
+ <pre>   &lt;extension
+        point=&quot;org.eclipse.core.runtime.contentTypes&quot;&gt;
+        &lt;content-type
+            id=&quot;topElementContentType&quot;
+            name=&quot;Tests top-level element recognition&quot;
+            base-type=&quot;org.eclipse.core.runtime.xml&quot;
+            priority=&quot;high&quot;&gt;
+            &lt;describer class=&quot;org.eclipse.core.runtime.content.XMLRootElementContentDescriber&quot;&gt;
+                &lt;parameter name=&quot;element&quot; value=&quot;myTag&quot; /&gt;
+            &lt;/describer&gt;
+        &lt;/content-type&gt;
+    &lt;/extension&gt;
+    &lt;extension
+        point=&quot;org.eclipse.core.runtime.contentTypes&quot;&gt;
+        &lt;content-type
+            id=&quot;dtdContentType&quot;
+            name=&quot;Tests dtd element recognition&quot;
+            base-type=&quot;org.eclipse.core.runtime.xml&quot;
+            priority=&quot;high&quot;&gt;
+            &lt;describer class=&quot;org.eclipse.core.runtime.content.XMLRootElementContentDescriber&quot;&gt;
+                &lt;parameter name=&quot;dtd&quot; value=&quot;myDTD.xml&quot; /&gt;
+            &lt;/describer&gt;
+        &lt;/content-type&gt;
+    &lt;/extension&gt;
+ </pre>
  <pre>   &lt;extension point = &quot;org.eclipse.ui.popupMenus&quot;&gt;
       &lt;objectContribution
              id=&quot;org.eclipse.ui.examples.objectContributions&quot;
-Line 37
+Line 97
                  nameFilter=&quot;*.xml&quot;&gt;
                  &lt;visibility&gt;
                          &lt;or&gt;
-                           &lt;objectState name=&quot;xmlFirstTag&quot; value=&quot;myTag&quot;/&gt;
+                    &lt;objectState
-                           &lt;objectState name=&quot;xmlDTDName&quot; value=&quot;myDTD.xml&quot;/&gt;
+                        name=&quot;contentTypeId&quot;
+                        value=&quot;org.eclipse.ui.examples.topElementContentType&quot;/&gt;
+                    &lt;objectState
+                        name=&quot;contentTypeId&quot;
+                        value=&quot;org.eclipse.ui.examples.dtdContentType&quot;/&gt;
                          &lt;/or&gt;
              &lt;/visibility&gt;
                  &lt;action id=&quot;org.eclipse.ui.examples.objectContributions.action1&quot;
-Line 78
+Line 142
                    &lt;packages prefixes=&quot;org.eclipse.ui, org.eclipse.jface&quot;/&gt;
             &lt;/library&gt;
          &lt;/runtime&gt;
- &lt;/fragment&gt;</pre>
+ &lt;/fragment&gt;
+ </pre>
  </blockquote>
+ <h3>BinarySignatureDescriber</h3>
- <p>A new parser, called PropertyParser, will be used to collect this information.
+ The BinarySignatureDescriber is a content describer to detect a specified binary
-   This parser will be a SAX based parser as we don't necessarily need to parse
+ 'signature' at a given offset within a file. This describer is used in the same
-   the entire file.</p>
+ fashion as the XMLRootElementContentDescriber with the exception that it takes
- <p>New persistent properties will be stored for any file that requires this information.
+ parameters &quot;signature&quot;, &quot;offset&quot; and &quot;required&quot;
-   First, a property called &quot;xmlLastMod&quot; will be used to store the last
+ instead of &quot;element&quot; or &quot;dtd&quot;. The Javadoc for BinarySignatureDescriber
-   modified time of the file (as know by IResource). This will ensure that we don't
+ gives complete details on this content describer's class usage.
-   re-parse this file if it isn't necessary. Two other properties, &quot;xmlFirstTag&quot;
-   and &quot;xmlDTDName&quot; will be used to store the name of the root level
-   tag and a DTD file (if specified) respectively. Note that if the parser is called
-   for either one of these, both will be stored (if they exist). The structure
-   of XML dictates that the DTD specification, if it exists, must occur before
-   the root level tag. As a result, once PropertyParser has parsed to the root
-   level tag, it's work is done. At this point, all other parsing is stopped.</p>
- <p>Any exceptions thrown by the parser are output to the .log file. PropertyParser
-   will explicitly test for an empty file as many SAX parsers will throw an exception
-   if they encounter an XML file without a root level tag.</p>
- <p>It should be noted that if a DTD is specified in a file, Crimson, a commonly
-   used SAX parser in Eclipse, requires that the DTD file exists and is readable.
-   If this is not the case, a SAXException will be thrown. The PropertyParser does
-   not require the DTD to be present, but the underlying parser often does.</p>
- <p>Related Bug Reports</p>
- <p>33018 - [Contributions] plugin.xml context menu should not have &quot;Run Ant...&quot;
-   item</p>
- <p>45024 - JAXP and old Xerces functionality</p>
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