@ -130,8 +130,7 @@ Basically, the document is a <code>StringBuilder</code> with events.
@@ -130,8 +130,7 @@ Basically, the document is a <code>StringBuilder</code> with events.
However, the <code>Document</code> namespace also contains several features that are useful to applications working with the text editor.
<p>In the text editor, all three controls (<code>TextEditor</code>, <code>TextArea</code>, <code>TextView</code>) have a <code>Document</code> property pointing to the <code>TextDocument</code> instance.
You can change the <code>Document</code> property to bind the editor to another document; but please only do so on the outermost control (usually <code>TextEditor</code>), it will inform its child controls about that change.
Changing the document only on a child control would leave the outer controls confused.
You can change the <code>Document</code> property to bind the editor to another document. It is possible to bind two editor instances to the same document; you can use this feature to create a split view.
<p><i>Simplified</i> definition of <code>TextDocument</code>:
<prelang="cs">public sealed class TextDocument : ITextSource
@ -205,7 +204,7 @@ You can customize the text area by modifying the <code>TextArea.DefaultInputHand
@@ -205,7 +204,7 @@ You can customize the text area by modifying the <code>TextArea.DefaultInputHand
WPF input bindings in it. You can also set <code>TextArea.ActiveInputHandler</code> to something different than the default
to switch the text area into another mode. You could use this to implement an "incremental search" feature, or even a VI emulator.
<p>
The text area has the useful <code>LeftMargins</code> property - use it to add controls to the left of the text view that look like
The text area has the <code>LeftMargins</code> property - use it to add controls to the left of the text view that look like
they're inside the scroll viewer, but don't actually scroll. The <code>AbstractMargin</code> base class contains some useful code
to detect when the margin is attached/detaching from a text view; or when the active document changes. However, you're not forced to use it;
any <code>UIElement</code> can be used as margin.
@ -233,7 +232,97 @@ The sample application to this article also contains the <code>BraceFoldingStrat
@@ -233,7 +232,97 @@ The sample application to this article also contains the <code>BraceFoldingStrat
However, it is a very simple implementation and does not handle { and } inside strings or comments correctly.
<h2>Syntax highlighting</h2>
TODO: write this section
The highlighting engine in AvalonEdit is implemented in the class <code>DocumentHighlighter</code>.
Highlighting is the process of taking a <code>DocumentLine</code> and constructing a <code>HighlightedLine</code> instance for it
by assigning colors to different sections of the line.
<p>
The <code>HighlightingColorizer</code> class is the only link between highlighting and rendering. It uses a <code>DocumentHighlighter</code>
to implement a line transformer that applies the highlighting to the visual lines in the rendering process.
<p>
Except for this single call, syntax highlighting is independent from the rendering namespace.
To help with other potential uses of the highlighting engine, the <code>HighlightedLine</code> class has the method
<code>ToHtml</code> to produces syntax highlighted HTML source code.
<p>
The rules for the highlighting are defined using an "extensible syntax highlighting definition" (.xshd) file.
Here is a complete highlighting definition for a sub-set of C#:
( \d+(\.[0-9]+)? #number with optional floating point
| \.[0-9]+ #or just starting with floating point
)
([eE][+-]?[0-9]+)? # optional exponent
</Rule>
</RuleSet>
</SyntaxDefinition></pre>
The highlighting engine works with "spans" and "rules" that each have a color assigned to them. In the XSHD format, colors can be both
referenced (<code>color="Comment"</code>) or directly specified (<code>fontWeight="bold" foreground="Blue"</code>).
<p>
Spans consist of two regular expressions (begin+end); while rules are simply a single regex with a color. The <code><Keywords></code> element is just a nice
syntax to define a highlighting rule that matches a set of words; internally a single regex will be used for the whole keyword list.
<p>
The highlighting engine works by first analyzing the spans: whenever a begin regex matches some text, that span is pushed onto a stack.
Whenever the end regex of the current span matches some text, the span is popped from the stack.
<p>
Each span has a nested rule set associated with it, which is empty by default.
This is why keywords won't be highlighted inside comments: the span's empty ruleset is active there, so the keyword rule is not applied.
<p>
This feature is also used in the string span: the nested span will match when a backslash is encountered, and the character following the backslash
will be consumed by the end regex of the nested span (<code>.</code> matches any character).
This ensures that <code>\"</code> does not denote the end of the string span; but <code>\\"</code> still does.
<p>
What's great about the highlighting engine is that it highlights only on-demand, works incrementally,
and yet usually requires only a few KB of memory even for large code files.
<p><i>On-demand</i> means that when a document is opened, only the lines initially visible will be highlighted. When the user scrolls down, highlighting will
continue from the point where it stopped the last time.
If the user scrolls quickly, so that the first visible line is far below the last highlighted line, then the highlighting engine still has to process all the
lines in between - there might be comment starts in them. However, it will only scan that region for changes in the span stack; highlighting rules will not
be tested.
<p>The stack of active spans is stored at the beginning of every line. If the user scrolls back up, the lines getting into view can be highlighted immediately
because the necessary context (the span stack) is still available.
<p><i>Incrementally</i> means that even if the document is changed, the stored span stacks will be reused as far as possible. If the user types <code>/*</code>, that would
theoretically cause the whole remainder of the file to become highlighted in the comment color. However, because the engine works on-demand, it will only update the
span stacks within the currently visible region and keep a notice 'the highlighting state is not consistent between line X and X+1', where X is the last line
in the visible region. Now, if the user would scroll down, the highlighting state would be updated and the 'not consistent' notice would be moved down.
But usually, the user will continue typing and type <code>*/</code> only a few lines later. Now the highlighting state in the visible region will revert to the
normal 'only the main ruleset is on the stack of active spans'. When the user now scrolls down below the line with the 'not consistent' marker;
the engine will notice that the old stack and the new stack are identical; and will remove the 'not consistent' marker. This allows reusing the stored span stacks
cached from before the user typed <code>/*</code>.
<p>While the stack of active spans might change frequently inside the lines, it rarely changes from the beginning of one line to the beginning of the next line.
With most languages, such changes happen only at the start and end of multiline comments. The highlighting engine exploits this property by storing
the list of span stacks in a special data structure (<code>ICSharpCode.AvalonEdit.Utils.CompressingTreeList</code>).
The memory usage of the highlighting engine is linear to the number of span stack changes; not to the total number of lines.
This allows the highlighting engine to store the span stacks for big code files using only a tiny amount of memory,
especially in languages like C# where sequences of <code>//</code> or <code>///</code> are more popular than <code>/* */</code> comments.
@ -77,6 +77,8 @@ However, the <code>Document</code> namespace also contains several features that
@@ -77,6 +77,8 @@ However, the <code>Document</code> namespace also contains several features that
<p>In the text editor, all three controls (<code>TextEditor</code>, <code>TextArea</code>, <code>TextView</code>) have a <code>Document</code> property pointing to the <code>TextDocument</code> instance.
You can change the <code>Document</code> property to bind the editor to another document; but please only do so on the outermost control (usually <code>TextEditor</code>), it will inform its child controls about that change.
Changing the document only on a child control would leave the outer controls confused.
<p>
It is possible to bind two editor instances to the same document; you can use this feature to create a split view.
<p><i>Simplified</i> definition of <code>TextDocument</code>:
<prelang="cs">public sealed class TextDocument : ITextSource
Daniel Grunwald
16 years ago