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<title>Into the Deep End of the SWT StyledText Widget</title>
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<div align="right">&nbsp; <font face="Times New Roman, Times, serif" size="2">Copyright
&copy; 2001,2002 International Business Machines Corp.</font>
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<td align=LEFT valign=TOP colspan="2" bgcolor="#0080C0"><b><font face="Arial,Helvetica"><font color="#FFFFFF">&nbsp;Eclipse
Corner Article</font></font></b></td>
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<h1><img src="Idea.jpg" height=86 width=120 align=CENTER></h1>
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<p>&nbsp;</p>
<h1 ALIGN="CENTER">Into the Deep End of the</h1>
<h1 ALIGN="CENTER">SWT StyledText Widget</h1>
<blockquote>
<b>Summary</b>
<p>The<i> StyledText</i> widget is a customizable widget that can be used to display and
edit text with different colors and font styles. In this article we discuss why you might
want to customize the <i>StyledText</i> widget and how you would do that. The article
assumes you are familiar with the concepts presented in our other article, <a
HREF="http://www.eclipsecorner.org/articles/StyledText%201/article1.html">&quot;Getting
Your Feet Wet With the SWT StyledText Widget&quot;</a>.</p>
<p><b>By Lynne Kues and Knut Radloff, OTI</b>
<br>
October 17, 2001; updated September 18, 2002 for Eclipse 2.0</p>
</blockquote>
<hr width="100%">
<h2>Overview</h2>
<p>The <i>StyledText</i> widget is designed as a pluggable widget. You can supply any or
all of the following components in order to customize the widget to your needs:
<ul>
<li>
<i>StyledTextContent</i> for storing and manipulating the widget&#146;s text. The <i>StyledText</i>
widget interacts with its <i>StyledTextContent</i> in order to access and update the text
that is being displayed and edited in the widget. </li>
<li>
<i>LineStyleListener</i> for answering the style information that is associated with the
widget&#146;s text. When the <i>StyledText</i> widget displays a line of text, it will ask
its <i>LineStyleListener</i> for the line&#146;s style information. </li>
<li>
<i>LineBackgroundListener</i> for answering background colors for the lines that are
displayed by the widget. When the <i>StyledText</i> widget displays a line, it will ask
its <i>LineBackgroundListener</i> for the line&#146;s background color. </li>
</ul>
<p>The <i>StyledText</i> widget supplies default implementations for all of the above
objects. Therefore, you can supply any combination of the above components. For example,
you could supply just a <i>StyledTextContent</i> implementation and use the <i>StyledText</i>
widget&#146;s default <i>LineStyleListener</i> and <i>LineBackgroundListener</i>.</p>
<h2>Implementing a StyledTextContent</h2>
<h3>StyledTextContent Applicability</h3>
<p>One of the main reasons to provide a content implementation for the <i>StyledText</i>
widget is to avoid data duplication. If the text that is to be displayed by the <i>StyledText</i>
widget is already stored and maintained in an object, you can eliminate data duplication
by providing a content implementation. </p>
<p>Providing your own <i>StyledTextContent</i> implementation will also give you more
flexibility since you will have direct access to the text content. For example, you may
want to manipulate the text independently of the widget. </p>
<h3>StyledTextContent Method Overview</h3>
<p>The <i>StyledTextContent </i>interface defines the protocol that is used by the <i>StyledText</i>
widget to get information about the text content it should display. The interface contains
all the methods that must be implemented in order to supply your own content
implementation. </p>
<i>
<p>void addTextChangeListener(TextChangeListener listener)</i>
<dir>
<p>This method is called by the <i>StyledText </i>widget in order to register itself as a
listener for content changes. The <i>StyledTextContent</i> implementer must store <i>TextChangeListeners
</i>and notify these listeners when content changes occur. Notification occurs in two
steps. First a <i>TextChangingEvent</i> should be sent when text content is about to
change and then a <i>TextChangedEvent</i> should be sent when the text content has
changed. Notification should occur in the <b>replaceTextRange</b> method (discussed
below).</p>
</dir>
<address>
int getCharCount()
</address>
<dl>
<dd>This method should return the number of characters in the text content. </dd>
</dl>
<i>
<p>String getLine(int lineIndex)</i>
<dir>
<p>This method should return the line at the given <i>lineIndex</i> without the line
delimiter.&nbsp; Line indexes are zero-based. For example:</p>
<pre><tt>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; line delimiter = &quot;\r\n&quot;
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; text content = &quot;Line 1\r\nLine2\r\nLine 3&quot;
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; </tt><i>getLine(0)</i><tt> should answer &quot;Line 1&quot;
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; </tt><i>getLine(2)</i><tt> should answer &quot;Line 3&quot;</tt></pre>
</dir>
<i>
<p>int getLineAtOffset(int offset)</i>
<dir>
<p>This method should return the index of the line at the given character <i>offset</i>.
Character offsets are zero-based.&nbsp; For example:</p>
<pre><tt>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; line delimiter = &quot;\n&quot;
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; text content = &quot;Line 1\nLine2\nLine 3&quot;
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; </tt><i>getLineAtOffset(6)</i><tt> should answer 0
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; </tt><i>getLineAtOffset(7)</i><tt> should answer 1</tt></pre>
</dir>
<i>
<p>int getLineCount()</i>
<dir>
<p>This method should return the number of lines in the text content.&nbsp;
For example:</p>
<pre><tt>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; line delimiter = &quot;\n&quot;
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; text content = &quot;Line 1\nLine2\nLine 3&quot;
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; </tt><i>getLineCount()</i><tt> should answer 3</tt></pre>
</dir>
<i>
<p>String getLineDelimiter()</i>
<dir>
<p>This method should return the line delimiter that should be used when
inserting new lines (i.e., via the keyboard) into the text content.</p>
</dir>
<i>
<p>int getOffsetAtLine(int lineIndex)</i>
<dir>
<p>This method should return the character offset of the first character
for the given <i>lineIndex</i>. Character offsets are zero-based.&nbsp; For example:</p>
<pre><tt>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; line delimiter = &quot;\r\n&quot;
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; text content = &quot;Line 1\r\nLine2\r\nLine 3&quot;
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; </tt><i>getOffsetAtLine(1)</i><tt> should answer 8
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; </tt><i>getOffsetAtLine(2)</i><tt> should answer 15</tt></pre>
</dir>
<i>
<p>String getTextRange(int start, int length)</i>
<dir>
<p>This method should return the text for the given range. The range begins
at character offset <i>start</i> and continues <i>length</i> characters. For example:</p>
<pre><tt>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; text content = &quot;Line 1\r\nLine2\r\nLine 3&quot;
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; </tt><i>getTextRange(3,8)</i><tt> should answer &quot;e 1\r\nLin&quot;</tt></pre>
</dir>
<i>
<p>void removeTextChangeListener(TextChangeListener listener)</i>
<ul>
<p>This method should remove a registered <i>TextChangeListener.</i> The
listener will no longer be notified of content changes.</p>
</ul>
<i>
<p>void replaceTextRange(int start, int length, String newText)</i>
<dir>
<p>This method should replace the given text range (beginning at offset <i>start</i>
and continuing for <i>replaceLength</i> characters) with <i>newText</i>. Before
the text update occurs, the <i>StyledTextContent</i> implementor should notify
its registered <i>TextChangeListeners</i> of the pending change. Notification
should occur via the <i>TextChangingEvent</i>.</p>
<dir> <tt>
<pre><font COLOR="#000080">public class</font> TextChangingEvent <font COLOR="#000080">extends</font> TypedEvent {
<font
COLOR="#000080">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; public int</font> newCharCount; <font
COLOR="#800000">// the length of the new text
</font>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <font
COLOR="#000080">public int</font> newLineCount; <font COLOR="#800000">// the number of new lines to be inserted
</font>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <font
COLOR="#000080">public</font> String newText;&nbsp;&nbsp;&nbsp;&nbsp; <font COLOR="#800000">// the text to be inserted
</font>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <font
COLOR="#000080">public int</font> replacedCharCount; <font COLOR="#800000">// the length of the text to be replaced
</font>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <font
COLOR="#000080">public int</font> replacedLineCount; <font COLOR="#800000">// the number of lines to be replaced
</font>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <font
COLOR="#000080">public int</font> start; <font COLOR="#800000">// the start offset of the text to be replaced
</font>}</pre>
</tt></dir>
<p>Note that <i>newLineCount<b> </b></i>and <i>replacedLineCount<b>
</b></i>should indicate the number of lines in the text to be inserted and the number of lines
in the text to be replaced, respectively. For example:</p>
</dir>
<div align="center"><center>
<table BORDER="1" CELLSPACING="2" BORDERCOLOR="#000000" CELLPADDING="7" WIDTH="576">
<tr>
<td WIDTH="22%" VALIGN="TOP"><p ALIGN="CENTER"><font FACE="Courier New" SIZE="2"><i>replaced
text</i></font></td>
<td WIDTH="28%" VALIGN="TOP"><font FACE="Courier New" SIZE="2"><i><p ALIGN="CENTER">inserted
text</i></font></td>
<td WIDTH="28%" VALIGN="TOP"><font FACE="Courier New" SIZE="2"><i><p ALIGN="CENTER">replacedLineCount</i></font></td>
<td WIDTH="22%" VALIGN="TOP"><font FACE="Courier New" SIZE="2"><i><p ALIGN="CENTER">newLineCount</i></font></td>
</tr>
<tr>
<td WIDTH="22%" VALIGN="TOP"><font FACE="Courier New" SIZE="2"><p ALIGN="CENTER">&quot;&quot;</font></td>
<td WIDTH="28%" VALIGN="TOP"><font FACE="Courier New" SIZE="2"><p ALIGN="CENTER">&quot;\n&quot;</font></td>
<td WIDTH="28%" VALIGN="TOP"><font FACE="Courier New" SIZE="2"><p ALIGN="CENTER">0</font></td>
<td WIDTH="22%" VALIGN="TOP"><font FACE="Courier New" SIZE="2"><p ALIGN="CENTER">1</font></td>
</tr>
<tr>
<td WIDTH="22%" VALIGN="TOP"><font FACE="Courier New" SIZE="2"><p ALIGN="CENTER">&quot;\n\n&quot;</font></td>
<td WIDTH="28%" VALIGN="TOP"><font FACE="Courier New" SIZE="2"><p ALIGN="CENTER">&quot;a&quot;</font></td>
<td WIDTH="28%" VALIGN="TOP"><font FACE="Courier New" SIZE="2"><p ALIGN="CENTER">2</font></td>
<td WIDTH="22%" VALIGN="TOP"><font FACE="Courier New" SIZE="2"><p ALIGN="CENTER">0</font></td>
</tr>
<tr>
<td WIDTH="22%" VALIGN="TOP"><font FACE="Courier New" SIZE="2"><p ALIGN="CENTER">&quot;a&quot;</font></td>
<td WIDTH="28%" VALIGN="TOP"><font FACE="Courier New" SIZE="2"><p ALIGN="CENTER">&quot;\n\n&quot;</font></td>
<td WIDTH="28%" VALIGN="TOP"><font FACE="Courier New" SIZE="2"><p ALIGN="CENTER">0</font></td>
<td WIDTH="22%" VALIGN="TOP"><font FACE="Courier New" SIZE="2"><p ALIGN="CENTER">2</font></td>
</tr>
<tr>
<td WIDTH="22%" VALIGN="TOP"><font FACE="Courier New" SIZE="2"><p ALIGN="CENTER">&quot;\n&quot;</font></td>
<td WIDTH="28%" VALIGN="TOP"><font FACE="Courier New" SIZE="2"><p ALIGN="CENTER">&quot;&quot;</font></td>
<td WIDTH="28%" VALIGN="TOP"><font FACE="Courier New" SIZE="2"><p ALIGN="CENTER">1</font></td>
<td WIDTH="22%" VALIGN="TOP"><font FACE="Courier New" SIZE="2"><p ALIGN="CENTER">0</font></td>
</tr>
</table>
</center></div>
<dir>
<p>After the text content is updated, the <i>StyledTextContent </i>implementor
should notify its registered <i>TextChangeListeners</i> that the change is complete.
Notification should occur via the <i>TextChangedEvent. </i>When the StyledText widget
receives this event, it will update the widget to reflect the change. The <i>TextChangedEvent</i>
does not contain any data since all the information about the change is included in the <i>TextChangingEvent</i>.
</p>
</dir>
<p><em>void setText(String newText)</em><font FACE="Courier New"
SIZE="2"> </font>
<dir>
<p>This method replaces the entire existing text with <i>newText</i>. Use
this method to initially specify the text content.</p>
</dir>
<p>Note that the <i>StyledTextContent</i> implementation does not deal with
text styles. It is only responsible for managing the text content.
The <i>LineStyleListener</i> and <i>LineBackgroundListener </i>objects manage style information. When
you implement a <i>StyledTextContent</i>, you are not required to implement a <i>LineStyleListener</i>
or a <i>LineBackgroundListener</i>. &nbsp; <em>StyledText's</em> default implementations
of <em>LineStyleListener</em> and <em>LineBackgroundListener</em> will not change style
information when a content change occurs.&nbsp; Styles for existing text will remain as
before the content change and new text will not be assigned any styles. If a content
change requires style changes, you can use the <b>replaceStyleRanges</b> (new since Eclipse 2.0) and
<b>setStyleRange</b> API to update the style information. When to update style information is
discussed below in the &quot;Text
Content/Style Update Processing&quot; section</p>
<h3>StyledTextContent Rules</h3>
<p>It is up to the <i>StyledTextContent</i> implementation to decide which
line delimiters it will recognize in order to determine the lines that are represented in
a text string. The default <i>StyledTextContent</i> implementation that is supplied with
the <i>StyledText</i> widget recognizes any combination of &quot;\n&quot;,
&quot;\r\n&quot;, and &quot;\r&quot; as line delimiters. Doing so ensures that strings
created with different line delimiters are interpreted correctly. Note that the delimiter
for a specific platform comes into play when new lines are inserted. When inserting text,
you want the new lines to be created with the platform line delimiter so that copy and
paste operations between platform applications work properly. You specify the delimiter to
use when inserting new text via the <b>getLineDelimiter </b>method. </p>
<p>As discussed above, when a text change occurs, the <i>StyledTextContent</i>
needs to send a <i>TextChangingEvent</i> and a <i>TextChangedEvent</i> to notify the <i>StyledText</i>
widget about the text change. Text changes can occur in one of three ways:
<ol TYPE="A">
<li>via the <i>StyledText</i> widget because of user input (e.g., keyboard
entry)</li>
<li>via the <i>StyledText</i> widget because API was called (e.g., <b>replaceTextRange
</b>or <b>paste</b>)</li>
<li>via your <i>StyledTextContent</i> implementation (i.e., your application
changes text independent of the <i>StyledText</i> widget)</li>
</ol>
<p>The following diagram indicates how these text changes occur within the <em>StyledText</em>
widget.&nbsp; The boxes in gray are discussed in length in our <a
HREF="http://www.eclipsecorner.org/articles/StyledText%201/article1.html">first article</a>,
&quot;Getting Your Feet Wet With the SWT StyledText Widget&quot;.&nbsp; For this article,
we will expand upon the processing that occurs in Step 4, &quot;Text Content/Style Update&quot;.</p>
<p ALIGN="CENTER"><img src="TextChanges.gif" width="420" height="995"
alt="TextChanges.gif (12968 bytes)"></p>
<div align="center"><b>Figure 1 &#150; Text Change Processing</b> </div>
<h4>Text Content/Style Update Processing </h4>
<p>The Text Content/Style Update process begins with the <em>StyledText</em>
widget or your application (for Case C) calling the<strong> replaceTextRange(int, int,
String)</strong> method.&nbsp; This method is the time and place to send the text change
events and to update your text content.&nbsp;&nbsp; How processing should occur is
depicted in the diagram below. The light gray boxes represent the processing that your <i>StyledTextContent</i>
implementation should perform, while the dark gray boxes represent the processing that
occurs in the <i>StyledText</i> widget.</p>
<font FACE="Courier New" SIZE="2">
<p ALIGN="CENTER">&nbsp;<img src="TextUpdate.gif" width="607" height="796"
alt="TextUpdate.gif (11618 bytes)"></p>
</font>
<div align="center"><b>Figure 2 &#150; Text Content/Style Update Processing</b> </div>
<p>The text content/style update process is started by sending the <i>TextChangingEvent</i>
(1). In response to this event, the <i>StyledText</i> widget prepares for the text change
by posting screen update operations for the area of the text change (2). After the <i>TextChangingEvent</i>
is sent, the application should update its text content to reflect the change (3), apply
style changes (4), and send the <i>TextChanged</i> event (5). When the <i>StyledText</i>
widget receives the <i>TextChangedEvent</i> it will update itself in accordance with the
change (e.g., scroll bars will be adjusted) and the text change will be visibly presented
in the <i>StyledText</i> widget (6). If you don't supply a <i>LineStyleListener</i>
as described below, part of the text change process will include updating the
style ranges to accommodate the text change (occurs in Step 2). As discussed in the first article
<a HREF="http://www.eclipsecorner.org/articles/StyledText%201/article1.html">
&quot;Getting Your Feet Wet With the SWT StyledText Widget&quot;</a>, the StyledText widget maintains
styles for existing text and does not apply styles for any new text. If the new text requires
styles or the existing styles need to be modified, this should be done in Step 4. </p>
<p>Note that the rules that apply to updating styles also apply to updating line background colors. If you do
not supply a <i>LineBackgroundListener</i> as described below, part of the text change process will
include updating line background colors if the text change includes adding or removing lines. As with styles,
the <i>StyledText</i> widget maintains existing line background colors. If the line
background colors need to be updated as a result of the text change, this should be done in Step 4.
</p>
<p>Note that between the time that your <em>StyledTextContent</em>
implementation sends the <i>TextChangingEvent</i> and the <i>TextChangedEvent</i>, your
implementation should not use API that will cause a scroll operation to occur or that will
cause posted paints to be flushed. The <i>StyledText</i> widget also does not handle
nested text content updates, so when processing text content changes, the application
should not use API that will cause text updates to occur.</p>
<p>The <i>StyledText</i> widget only modifies the cursor location when text
is changed via user input. In all other instances (i.e., Case B and Case C in Figure 1
above), if the application wishes the cursor location to change as a result of the text
content change, the following methods can be used to set the cursor location to an offset
and to make that offset visible: </p>
<tt>
<pre>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; setSelection(offset, 0)
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; showSelection()</pre>
</tt>
<h3>StyledTextContent Considerations</h3>
<p>When implementing a <i>StyledTextContent</i>, the algorithm for updating
the text content when modifications occur must be fast. If it is not, you will experience
sluggishness during typing (i.e., as your <i>StyledTextContent</i> attempts to deal with
the text change). Similarly, the algorithm for returning the text for a line should be
fast. If it is not, you will experience sluggishness during scrolling. It is also
important to ensure that your implementation scales well. When the text content gets
larger, handling of text replace operations and answering lines should not be adversely
affected from a performance standpoint. </p><p>
For an example of a <i>StyledTextContent</i> implementation, refer to the class <i>org.eclipse.swt.custom.DefaultContent</i>.
<i>DefaultContent</i> is the content implementation that the <i>StyledText</i> widget uses
by default. </p>
<h3>StyledTextContent Implementation Validation</h3>
<p>The following Java&trade; class can be used to test a <i>StyledTextContent</i>
implementation. When executed, the class will run through a number of test scenarios that
exercise the <i>StyledTextContent</i> interface. To use the class, import it into the
package that contains your <i>StyledTextContent</i> implementation. Then specify the fully
qualified name of your implementation class as an argument to the<i>
StyledTextContentSpec&#146;s</i> <b>main</b> method.&nbsp; As each test scenario is
executed, <b>System.out</b> will be updated to indicate whether or not each test
passed.&nbsp; Note that this class is designed to work with a <em>StyledTextContent</em>
implementation that supports &quot;\r&quot;, &quot;\n&quot;, and '\r\n&quot; as line
delimiters.</p>
<p><a HREF="StyledTextContentSpec.java">StyledTextContentSpec.java</a> <br>
</p>
<h2>Implementing a LineStyleListener</h2>
<h3>LineStyleListener Applicability</h3>
<p>One of the main reasons to use a customized <i>LineStyleListener</i> is
to support on-demand line styling. Instead of using the <b>replaceStyleRanges</b> (new in Eclipse 2.0),
<b>setStyleRanges</b> and <b>setStyleRange</b>
methods to statically set the style information for the widget&#146;s text,
style information can be provided dynamically on a line-by-line basis. </p>
<p>If styles are determined based on the actual text content, on-demand line styling can
be used since the text of each line is passed to the <i>LineStyleListener</i>. Text styles
that are used for syntax highlighting can typically be provided dynamically. For example,
except for block comments, all of Java&#146;s syntactic elements occur on one line. It
would be more efficient to use a dynamic, customized<i> LineStyleListener </i>vs. the <i>StyledText</i>
API to implement Java syntax highlighting. If you used the <i>StyledText</i> API, style
information would be maintained statically and any time text changes occurred this
information would have to be updated (e.g., via the <b>setStyleRange</b> API). Using the <i>StyledText</i>
API would also require you to parse the entire text up front. If on-demand line styling
were used, the text would be parsed on an as needed basis, as it is displayed, thus
improving initial load time. </p>
<p>Another reason to use a customized <i>LineStyleListener</i> is to avoid duplicating
data. When the <i>StyledText</i> methods <b>replaceStyleRanges</b>, <b>setStyleRanges</b> and <b>setStyleRange </b>are
called, the <i>StyledText</i> widget will cache the <i>StyleRange</i> objects that are
supplied as input parameters. However, if the information needed to construct style ranges
is already stored by an object in your application, introducing a <i>LineStyleListener</i>
that uses this object may be beneficial. </p>
<p>You may also use a customized <i>LineStyleListener</i> in order to provide
application-specific text coloring behavior. By default, when text changes occur in the <i>StyledText</i>
widget, text colors are updated as follows:
<ol>
<ol>
<li>If text is deleted, its associated style will also be deleted.</li>
<li>If new text is inserted, it&#146;s associated style will be null (i.e.,
the text background color will be the widget background color, the text foreground color
will be the widget foreground color, and the text font style will be the widget font
style).</li>
</ol>
</ol>
<dir>
<dir>
<dir>
<p>Note: A text replace operation is treated as a text delete operation
followed by a text insert operation.</p>
</dir>
</dir>
</dir>
<p>The <i>StyledText</i> widget does not make any assumptions about how to
apply styles when text is inserted or deleted because how to update the styles will depend
on how the <i>StyledText</i> widget is being used. For example, if the widget is being
used to support syntax highlighting for a source code editor, coloring will occur only
when inserted text completes a keyword. Whereas, if the widget is being used to support
text attributes for a word processor, inserted text will most likely take on the style
values of the characters adjacent to the text. To provide specific text style updating
behavior you can introduce your own <i>LineStyleListener</i>.</p>
<h3>LineStyleListener Method Overview</h3>
<p>The <i>LineStyleListener </i>interface defines the protocol that is used
by the <i>StyledText</i> widget to get the styles of a displayed line.</p>
<i>
<p>void lineGetStyle (LineStyleEvent event) </i>
<dir>
<p>The <b>lineGetStyle</b> method is called when a line is about to be
drawn in order to get the line&#146;s style information. When the method is called, the <i>LineStyleEvent</i>
has two input fields set - <b>LineStyleEvent.lineOffset</b> contains the start offset of
the line and&nbsp; <b>LineStyleEvent<font COLOR="#000080">.</font>lineText</b> contains
the text of the line. It is your responsibility to set the output field, <b>LineStyleEvent.styles</b>.
This field defines the StyleRanges for the text line. The widget uses the StyleRanges for
measuring and rendering text when the <b>lineGetStyle</b> listener method returns. Each <i>StyleRange</i>
object describes the foreground color, background color and font style for a range of text
in the particular line your listener was called for. The range start offset is relative to
the beginning of the document, not the beginning of the line.</p>
</dir>
<h3>LineStyleListener Rules</h3>
<p>If you implement your own <i>LineStyleListener </i>to supply line styles
you may no longer use the <b>replaceStyleRanges</b>, <b>setStyleRange, setStyleRanges</b> or <b>getStyleRange</b>
API. You can supply style information using a <i>LineStyleListener </i>or the API, but not
both. </p><p>
Ideally, you only have to use the line text and offset information supplied in the <i>LineStyleEvent</i>
passed in to the <b>lineGetStyle</b> listener method to calculate line style information.
However, it may be necessary for you to store style information and simply look up the
styles when your listener method is called. In this case, you will have to update the
style information when text changes occur. To do this, you can listen to the <b>extended
modify event</b> (described in detail in our <a
HREF="http://www.eclipsecorner.org/articles/StyledText%201/article1.html">first article</a>).
The <b>extended modify event</b> is sent after the widget text has been updated, but
before the screen updates take effect. In this manner, inserted text can immediately use
any styles that have been specified. Note that it does not make sense to use the <b>modify
event</b> to update styles in this manner since the <b>modify event</b> does not contain
any specific information about the text change (e.g., character offset of the inserted
text).&nbsp;<a NAME="StyleRedraw"></a> &nbsp; </p>
<p>If, as a result of the text change, style information before or after the lines
modified by the text change is changed, you will have to redraw the affected area of the
widget. For example, if you are using the <i>StyledText</i> widget for java syntax
highlighting in a source code editor, deleting the beginning of a block comment (i.e.,
&quot;/*&quot;) will affect lines after the line on which the text change occurred. In
this instance, it would be the application&#146;s responsibility to redraw the other
comment lines. The <i>StyledText</i> widget will only update text lines based on the text
change that occurred.</p>
<p>The <i>StyledText</i> widget provides two redraw methods to support the above
scenarios: </p>
<tt>
<pre> <font COLOR="#000080">public void</font> redrawRange(<font COLOR="#000080">int</font> start, <font
COLOR="#000080">int</font> length, <font COLOR="#000080">boolean</font> clearBackground)
<font
COLOR="#000080">public void</font> redraw(<font COLOR="#000080">int</font> x, <font
COLOR="#000080">int</font> y, <font COLOR="#000080">int</font> width, <font
COLOR="#000080">int</font> height, <font COLOR="#000080">boolean</font> all)</pre>
</tt>
<p>The first, <b>redrawRange</b>, lets you specify the exact text range to
redraw using character offsets. The second method, <b>redraw</b>, is the standard SWT
redraw method that redraws a pixel based rectangle in the widget. SWT provides another
redraw method, which is not shown here. It does not have any arguments and redraws the
whole widget. You can use this method, but it will cause the text to flash since it
performs a full clear and redraw of the widget.</p>
<h3>LineStyleListener Considerations</h3>
<p>If you implement your own <i>LineStyleListener</i>, keep in mind that
the listener is called every time a line is rendered or scrolled and when a key is
pressed. It is therefore important that the <b>lineGetStyle</b> method is fast and that it
scales well for use with large amounts of text. If you experience a lag when typing and
scrolling, your <i>LineStyleListener </i>implementation is too slow. If typing and
scrolling is slow at the end of the text, your algorithm does not scale well. Note that
unresponsive typing may also be caused by slow processing in <i>VerifyListeners</i>, <i>ModifyListeners</i>
or <i>ExtendedModifyListeners </i>(see our <a
HREF="http://www.eclipsecorner.org/articles/StyledText%201/article1.html">first article</a>
for more information about verify and modify listeners). </p>
<p>If you implement a <i>LineStyleListener </i>and store the <i>StyleRange</i> objects
(instead of calculating them on demand) it is advisable to merge adjacent styles that have
the same style data. Merging StyleRanges improves the performance of text measuring and
rendering in the <i>StyledText</i> widget because fewer <i>StyleRange</i> objects have to
be processed. </p>
<p><a NAME="LineStyleListenerRedraw"></a>If you redraw text during the <b>extended
modified event</b>, make sure that you only redraw text ranges that actually have new
styles. Unnecessary refresh operations can cause flash and degrade performance. See the
discussion in the &quot;Text Refresh&quot; section of our <a
HREF="http://www.eclipsecorner.org/articles/StyledText%201/article1.html">first article</a>
for more information about what flash means and what causes it. </p>
<p>For an example of a <i>LineStyleListener</i> implementation, refer to the class <i>org.eclipse.swt.custom.DefaultLineStyler</i>.
This class&#146; implementation of the <i>LineStyleListener</i> interface is the
implementation that the <i>StyledText</i> widget uses by default. The class illustrates
the concepts discussed above, including how to merge neighboring styles </p>
<h3>LineStyleListener Example</h3>
<p>The following example is the <b>lineGetStyle</b> method from a <i>LineStyleListener
</i>that implements a simple Java syntax coloring strategy. The method constructs
the <em>StyleRange</em> objects dynamically (i.e., every time they are requested)
and merges similar styles for improved rendering performance.&nbsp; The example
method code is taken from the SWT Java Syntax Viewer example, which is part
of the example plugins that can be downloaded with the Eclipse SDK.&nbsp; The
example code can be found in the plugins subdirectory<em> </em>org.eclipse.swt.examples.&nbsp;
Three classes comprise the example - <em>JavaViewer</em>, <em>JavaLineStyler</em>
and <em>JavaScanner</em>. &nbsp; The <em>JavaScanner</em> class is an inner
class of <em>JavaLineStyler</em>.</p>
<p>The <i>JavaScanner</i> class implements a Java syntax scanner. The <i>JavaScanner</i>
public API includes the methods: </p>
<tt>
<pre> <font COLOR="#000080">void</font> setRange(String)
<font COLOR="#000080">int</font> nextToken()&nbsp;
<font
COLOR="#000080">int</font> getStartOffset()
<font COLOR="#000080">int</font> getLength()</pre>
</tt>
<p>as well as constants for the different Java syntax elements that need
highlighting. In addition, the method <b>Color getColor(int)</b> returns a <i>Color</i>
object for a given Java syntax constant. </p>
<p>In the example, we set the text of the line we want to syntax scan in the Java scanner.
We apply different colors to each token and keyword tokens are given a font style of bold.
If the color for a token differs from the widget foreground color or if the token is a
keyword (in which case a <i>StyleRange</i> would be necessary in order to specify a bold
font style), we create a new <i>StyleRange</i> object for that element. If the previous <i>StyleRange</i>
object has the same foreground color, background color and font style, it is considered
similar and the two ranges can be merged. Merging StyleRanges improves the performance of
text measuring and rendering in the <i>StyledText</i> widget.</p>
<p>The lineGetStyle method also includes special processing for handling the <i>StyleRanges</i>
that are created for keywords. In Java code, multiple keywords are often grouped together
(e.g., &quot;public static final int&quot;). To minimize the number of <i>StyleRanges</i>
that are created in this instance, spaces between the keywords are assigned a bold font
style. This strategy will lead to only one <i>StyleRange</i> for a group of keywords vs.
multiple <i>StyleRanges</i> (i.e., one for each keyword and one for each space between the
keywords).&nbsp; The strategy will also minimize the number of font style changes that
occur during rendering (i.e., the number of changes from the normal font to the bold
font).</p>
<p>When the complete line has been scanned and processed, the styles are copied into the <i>LineStyleEvent</i>.
<dir>
<dir>
<tt><pre><font COLOR="#000080">public</font> <font COLOR="#000080">void</font> lineGetStyle(LineStyleEvent event) {
Vector styles = <font
COLOR="#000080">new</font> Vector();
<font COLOR="#800000"> // If the line is part of a block comment, create one style for the entire line.
</font> <font
COLOR="#000080">if</font> (inBlockComment(event.lineOffset, event.lineOffset + event.lineText.length())) {
styles.addElement(new StyleRange(event.lineOffset, event.lineText.length(), getColor(COMMENT), <font
COLOR="#000080">null</font>));
event.styles = <font COLOR="#000080">new</font> StyleRange[styles.size()];
styles.copyInto(event.styles);
<font
COLOR="#000080">return</font>;
}
<font COLOR="#000080"> int</font> token;
StyleRange lastStyle;
Color defaultFgColor = ((Control)event.widget).getForeground();
scanner.setRange(event.lineText);
token = scanner.nextToken();
<font
COLOR="#000080">while</font> (token != EOF) {
<font COLOR="#000080">if</font> (token == OTHER) {
<font
COLOR="#800000"> // no syntax highlighting necessary
</font> } <font
COLOR="#000080">else</font> <font COLOR="#000080">if</font> ((token != WHITE) {
<font
COLOR="#800000"> // Only create a style if the token color is different than the widget's default foreground color and the
// token&#146;s fontStyle is not bold.
</font> Color color = getColor(token);
<font
COLOR="#000080"> if</font> ((!color.equals(defaultFgColor)) || (token == KEY)) {
StyleRange style = new StyleRange(scanner.getStartOffset() + event.lineOffset, scanner.getLength(), color, <font
COLOR="#000080">null</font>);
<font COLOR="#000080">if</font> (token == KEY) {
style.fontStyle = SWT.BOLD;
}
<font
COLOR="#000080">if</font> (styles.isEmpty()) {
styles.addElement(style);
} <font
COLOR="#000080">else</font> {
<font COLOR="#800000"> // Merge similar styles.
</font> lastStyle = (StyleRange)styles.lastElement();
<font
COLOR="#000080">if</font> (lastStyle.similarTo(style) &amp;&amp; (lastStyle.start + lastStyle.length == style.start)) {
lastStyle.length += style.length;
} <font
COLOR="#000080">else</font> {
styles.addElement(style);
}
}
}
} <font
COLOR="#000080">else if</font> (!styles.isEmpty()) &amp;&amp; ((lastStyle=(StyleRange)styles.lastElement()).fontStyle == SWT.BOLD)) {
<font
COLOR="#800000"> // Have the white space take on the bold style before it to minimize the number of style ranges.
</font> <font
COLOR="#000080">int</font> start = scanner.getStartOffset() + event.lineOffset;
<font
COLOR="#800000"> </font><font COLOR="#000080">if</font> (lastStyle.start + lastStyle.length == start) {
<font
COLOR="#800000"> </font>lastStyle.length += scanner.getLength();
}
}
token= scanner.nextToken();
}
event.styles = new StyleRange[styles.size()];
styles.copyInto(event.styles);
}
</pre>
</tt></dir>
</dir>
<h2>Implementing a LineBackgroundListener</h2>
<h3>LineBackgroundListener Applicability</h3>
<p>As with the LineStyleListener, one reason to use a customized <i>LineBackgroundListener</i>
is to avoid duplicating data. When the <i>StyledText</i> method <b>setLineBackground</b>
is called, the <i>StyledText</i> widget will cache the colors for the specified lines. If
this information is already stored by an object in your application, introducing a <i>LineBackgroundListener</i>
that interacts with this object will eliminate data duplication. </p>
<p>You may also use a customized <i>LineBackgroundListener</i> in order to provide
application-specific line background coloring behavior. The <i>StyledText</i> widget
maintains line background colors relative to text lines. By default, when text changes
occur in the <i>StyledText</i> widget, line background colors are updated as follows:
<ol>
<ol>
<li>If a line is deleted, its associated line background color will also be deleted.</li>
<li>If a new line is inserted, its associated line background color will be null (i.e., the
widget background color) and line background colors for existing lines of text are
unchanged.</li>
</ol>
</ol>
<p>For example, in the window below, a line background color of gray is used to emphasize
the import statements. If text lines are inserted or deleted, you would want the line
background color that is associated with the block of import statements to be maintained. </p>
<p ALIGN="CENTER"><img SRC="Image8.gif" WIDTH="427" HEIGHT="169"></p>
<p>
<font SIZE="2"><br>
</font>Your application may want line background colors to be updated
differently when text changes occur. For example, if you want the background of every
other line to be gray (e.g., in order to facilitate reading tabulated text), you would
need to &quot;shift&quot; line background colors as lines are deleted or inserted. You
could easily support this behavior by implementing your own <i>LineBackgroundListener</i>.</p>
<h3>LineBackgroundListener Method Overview</h3>
<p>The <i>LineBackgroundListener</i> interface defines the protocol that is
used by the <i>StyledText</i> widget to get the line background colors to use when
displaying the text. The interface, <i>LineBackgroundListener</i>, contains the methods
that must be implemented in order to supply your own line background color implementation.
</p>
<i>
<p>void lineGetBackground(LineBackgroundEvent event)</i>
<dir>
<p>This method is called when a line is to be drawn in order to get the line&#146;s
background color. <i>LineBackgroundEvent</i> will contain the start offset, <b>lineOffset</b>,
and the text, <b>lineText</b>, of the line to be drawn. Fill in the background color in
the <b>lineBackground</b> field. A value of null indicates that the default widget
background should be used for the line. <br>
&nbsp;</p>
</dir>
<p>In the following example, a LineBackgroundListener is used to color the background of
every other line to light gray. The method assumes that we have a cache of colors indexed
by RGB value.
<dir>
<dir>
<tt><pre><font COLOR="#000080">public void</font> lineGetBackground(LineBackgroundEvent event) {
<font
COLOR="#000080">int</font> line = ((StyledText) event.widget).getLineAtOffset(event.lineOffset);
<font
COLOR="#000080">if</font> ((line % 2) == 1) {
event.lineBackground = (Color)colors.get(<font
COLOR="#000080">new</font> RGB(222, 222, 222));
}
}</pre>
</tt></dir>
</dir>
<h3>LineBackgroundListener Rules</h3>
<p>Line background colors are drawn for the width of the widget, not the
width of the text. If a text background color is defined (i.e., via a <i>StyleRange</i>),
this color will overlay the line background color. </p>
<p>If you implement your own <i>LineBackgroundListener, </i>the following <i>StyledText</i>
methods are not applicable and should not be used since your <i>LineBackgroundListener</i>
will be maintaining and storing line background colors:
<dir>
<dir>
<p><tt><font COLOR="#000080">public</font> Color getLineBackground(<font COLOR="#000080">int</font>
index)</tt><font SIZE="2"> <br>
</font><tt><font COLOR="#000080">public</font> <font COLOR="#000080">void</font>
setLineBackground(<font COLOR="#000080">int</font> startLine, <font COLOR="#000080">int</font>
lineCount, Color background)</tt> </p>
</dir>
</dir>
<h3>LineBackgroundListener Considerations</h3>
<p>When you implement a <i>LineBackgroundListener</i>, since the <b>setLineBackground</b>
API is no longer available, you will be responsible for refreshing line background colors
within the widget. For example, if a text content change alters line background colors for
lines other than the lines on which the text change occurred, it would be the
LineBackgroundListener&#146;s responsibility to redraw these lines. You can refresh line
background colors by using the <b>redraw(int x, int y, int width, int</b><b>height, boolean all)</b> method. The input parameters
to this method specify a pixel-based rectangle. You can use other <i>StyledText</i> API
(e.g., <b>getLocationAtOffset</b>) to calculate the rectangle for a line. </p><p>
<a NAME="LineBackgroundListenerRedraw"></a>When you implement a <i>LineBackgroundListener</i>
you should make sure that you only initiate line background updates when necessary.
Unnecessary refreshing of lines will cause flash and degrade performance of the <i>StyledText</i>
widget, as discussed in the Text Refresh section of our <a
HREF="http://www.eclipsecorner.org/articles/StyledText%201/article1.html">first article</a>.</p><p>
For an example of how to implement a <i>LineBackgroundListener</i>, refer to the class <i>org.eclipse.swt.custom.DefaultLineStyler</i>.
The <i>DefaultLineStyler </i>implements the<i> LineBackgroundListener</i> behavior that
the <i>StyledText</i> widget uses by default.
<dl>
<dt>&nbsp;</dt>
</dl>
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