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| <TITLE>Implementing a Content Viewer</TITLE> |
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| <H2> |
| Implementing a content viewer</H2> |
| |
| |
| <p> |
| The compare plug-in allows you to supply specialized viewers for viewing and |
| merging content differences between unstructured elements.</p> |
| |
| |
| <h3> |
| Simple content viewers</h3> |
| |
| |
| <p> |
| A <b>content viewer</b> is used in places where only a single input is available and therefore |
| no compare is necessary. A typical example for this is the "<b>Restore from Local |
| History</b>" function. The <a href="../reference/extension-points/org_eclipse_compare_contentViewers.html"><b>org.eclipse.compare.contentViewers</b></a> |
| extension point allows you to define a specialized content viewer that does not |
| compare its inputs.</p> |
| |
| |
| <h3> |
| Content merge viewers</h3> |
| |
| |
| <p> |
| A <b> content merge viewer </b> performs a two-way or three-way compare of its inputs |
| and presents the result |
| side-by-side or in any other suitable way. The viewer lets the user merge between the inputs. |
| Content merge viewers are common for text or images.</p> |
| |
| |
| <p>If the standard merge viewers are not appropriate for your plug-in's |
| function, you may choose to implement your own content viewer. Your |
| content viewer should be registered with the platform using the |
| <a href="../reference/extension-points/org_eclipse_compare_contentMergeViewers.html"><b>org.eclipse.compare.contentMergeViewers</b></a> |
| <b> </b>extension point. The following markup shows |
| the definition of specialized content merge viewers for viewing Java and |
| properties files in the Java IDE:</p> |
| |
| |
| <pre><font color="#4444CC"><extension |
| point="org.eclipse.compare.contentMergeViewers"> |
| <viewer |
| id="org.eclipse.jdt.internal.ui.compare.JavaContentViewerCreator" |
| extensions="java,java2" |
| class="org.eclipse.jdt.internal.ui.compare.JavaContentViewerCreator"> |
| </viewer> |
| <viewer |
| id="org.eclipse.jdt.internal.ui.compare.TextMergeViewerCreator" |
| extensions="properties" |
| class="org.eclipse.jdt.internal.ui.compare.TextMergeViewerCreator"> |
| </viewer> |
| </extension> |
| </pre></font> |
| |
| |
| <p> In the markup, you specify the <b>id </b>of the viewer, the <b>class</b> that |
| creates it, and the file <b>extension</b> |
| for which the content viewer should be used. </p> |
| |
| |
| <p> <a href="../reference/api/org/eclipse/compare/contentmergeviewer/ContentMergeViewer.html"><b>ContentMergeViewer</b></a> |
| is an abstract compare and merge viewer |
| with two side-by-side content areas and an optional content area for a |
| common ancestor (for three-way compare). Because the implementation makes |
| no assumptions about the content type, the subclass is responsible for dealing |
| with the specific content type. </p> |
| |
| |
| <p> <b>ImageMergeViewer</b> in <b> org.eclipse.compare.internal</b> shows how to |
| implement a simple merge viewer for images using a <a href="../reference/api/org/eclipse/compare/contentmergeviewer/ContentMergeViewer.html"><b>ContentMergeViewer</b></a>. |
| A <a href="../reference/api/org/eclipse/compare/contentmergeviewer/ContentMergeViewer.html"><b>ContentMergeViewer</b></a> |
| accesses its model by means of a content |
| provider which must implement the |
| <a href="../reference/api/org/eclipse/compare/contentmergeviewer/IMergeViewerContentProvider.html"><b>IMergeViewerContentProvider</b></a> interface.</p> |
| |
| |
| <h4> Text merging</h4> |
| |
| |
| <p> If your viewer uses text, additional classes that compare |
| and merge text content can be used.</p> |
| <p> |
| <a href="../reference/api/org/eclipse/compare/contentmergeviewer/TextMergeViewer.html"><b>TextMergeViewer</b></a> |
| is the concrete subclass of |
| <a href="../reference/api/org/eclipse/compare/contentmergeviewer/ContentMergeViewer.html"><b>ContentMergeViewer</b></a> |
| used for comparing and merging text content. A text merge viewer uses the |
| <a href="../reference/api/org/eclipse/compare/rangedifferencer/RangeDifferencer.html"><b>RangeDifferencer</b></a> |
| to perform a textual, line-by-line comparison of two (or three) input documents. |
| <p> |
| For text lines that differ, the |
| <a href="../reference/api/org/eclipse/compare/contentmergeviewer/TextMergeViewer.html"><b>TextMergeViewer</b></a> |
| uses an |
| <a href="../reference/api/org/eclipse/compare/contentmergeviewer/ITokenComparator.html"><b>ITokenComparator</b></a> |
| to find the longest sequences of matching and non-matching tokens. |
| The |
| <a href="../reference/api/org/eclipse/compare/contentmergeviewer/TextMergeViewer.html"><b>TextMergeViewer</b></a>'s |
| default token compare works on characters separated by white space. If a |
| different strategy is needed (for example, Java tokens in a Java-aware |
| merge viewer), clients can create their own token comparators by implementing |
| the |
| <a href="../reference/api/org/eclipse/compare/contentmergeviewer/ITokenComparator.html"><b>ITokenComparator</b></a> |
| interface. |
| <p> |
| <a href="../reference/api/org/eclipse/compare/contentmergeviewer/TextMergeViewer.html"><b>TextMergeViewer</b></a> |
| works on whole documents and on sub ranges of documents. For partial documents, |
| the viewer's input must be an |
| <a href="../reference/api/org/eclipse/compare/contentmergeviewer/IDocumentRange.html"><b>IDocumentRange</b></a> |
| instead of an |
| <a href="../reference/api/org/eclipse/jface/text/IDocument.html"><b>IDocument</b></a>. |
| <h4>Range differencing</h4> |
| <p> |
| <a href="../reference/api/org/eclipse/compare/rangedifferencer/RangeDifferencer.html"><b>RangeDifferencer</b></a> |
| finds the longest sequences of matching and |
| non-matching comparable entities in text content. Its implementation is based on |
| an objectified version of the algorithm described in: |
| <i>A File Comparison Program,</i> by Webb Miller and Eugene W. Myers, |
| Software Practice and Experience, Vol. 15, Nov. 1985. Clients must supply |
| an input to the differencer that implements the |
| <a href="../reference/api/org/eclipse/compare/rangedifferencer/IRangeComparator.html"><b>IRangeComparator</b></a> |
| interface. |
| <a href="../reference/api/org/eclipse/compare/rangedifferencer/IRangeComparator.html"><b>IRangeComparator</b></a> |
| breaks the input data into a sequence |
| of entities and provides a method for comparing |
| one entity with the entity in another |
| <a href="../reference/api/org/eclipse/compare/rangedifferencer/IRangeComparator.html"><b>IRangeComparator</b></a>. |
| <p> |
| |
| For example, to compare two text documents and find the longest common |
| sequences of matching and non-matching lines, |
| the implementation of |
| <a href="../reference/api/org/eclipse/compare/rangedifferencer/IRangeComparator.html"><b>IRangeComparator</b> </a> |
| must break the document into lines and provide a method for testing |
| whether two lines are considered equal. |
| See <b>org.eclipse.compare.internal.DocLineComparator</b> for an example of how this can be done. |
| <p> |
| |
| The differencer returns the differences among these sequences as an |
| array of |
| <a href="../reference/api/org/eclipse/compare/rangedifferencer/RangeDifference.html"><b>RangeDifference</b></a> |
| objects. |
| Every single |
| <a href="../reference/api/org/eclipse/compare/rangedifferencer/RangeDifference.html"><b>RangeDifference</b></a> |
| describes the kind of difference |
| (no change, change, addition, deletion) and the corresponding ranges |
| of the underlying comparable entities in the two or three inputs. |
| <p> |
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