Custom Text (Code) Areas in QTextEdit

Question

I'm interested in creating a type of text object (inheriting from QTextObjectInterface ) that behaves like a code region:

• distinctive background
• the border
• fixed width font
• editable content
• instances must be identifiable for the code, so the contents inside them can be extracted (separate code from the surrounding content)
• save / load (from regular html files)
• syntax highlighting will be a plus, but not really required

Other areas of the document should behave in the usual way (font properties are editable, editable colors, etc.).

---

Qt provides an example for implementing custom text objects with QTextEdit . This looks complicated because the new text object cannot use the existing infrastructure inside QTextEdit / QTextDocument .

QTextObject

base class for various types of objects that can group parts of a QTextDocument together

therefore, inheritance may be a choice, but neither its source files in the Qt SDK package, nor Google search queries showed useful information.

A QTextFrame inherits a QTextObject , so again, it can be a valid base class if you need to find some clues about this path.

---

In a simple HTML file, all this (except for syntax highlighting) would be simple. QTextEdit accepts html as input file and can export html, but the structure is lost in the process.

<code class="code-sample"> int i = 0; </code> 

QWebView is read-only. He advertises that:

Parts of HTML documents can be edited, for example, through the contenteditable attribute for HTML elements.

---

There may be other platforms where this is available, but a text editor needs to be used inside Qt Creator as a plug-in, so using a Qt infrastructure makes sense.

Bottom line: how to implement code areas in a QTextEdit widget?

---

Late changes:

• using Qt sdk from trunk (identifies itself as 4.8.4)
• Qt Creator from the torso (Qt Creator 2.6.81)

Answer 1

I found that implementing this is possible using QTextEdit / QTextDocument. The simplest implementation that I can think of is presented in this answer for the reference of the future seeker.

Please note that saving / loading must be configured as regular .toHtml (), without saving the necessary information.

Inserting code is very simple:

 QTextFrame * frame; frame = cursor.insertFrame( code_block_format_ ); connect( frame, SIGNAL( destroyed() ), this, SLOT( codeBlockDeleted() ) ); code_blocks_.append( frame ); 

pay attention to two variables that you can save in the class:

 QTextFrameFormat code_block_format_; QList<const QTextFrame*> code_blocks_; 

We need a format so that it is consistent and distinctive. Its mat is initialized in the constructor like this:

 code_block_format_.setBackground( QBrush( Qt::yellow ) ); code_block_format_.setBorder( 1 ); code_block_format_.setBorderStyle( QTextFrameFormat::BorderStyle_Inset); code_block_format_.setMargin( 10 ); code_block_format_.setPadding( 4 ); 

We need a list so that we can determine if a particular frame is coded or not. Since all objects that inherit from QTextObject must be created by QTextDocument :: createObject (), we cannot simply subclass QTextFrame (in fact, I think we can, but are not sure yet).

Now the separation of the contents of the code from the rest can be performed in the usual way:

 for ( it = frame->begin(); !(it.atEnd()); ++it ) { child_frame = it.currentFrame(); child_block = it.currentBlock(); if ( child_frame != NULL ) { if ( code_blocks_.contains( frame ) ) { /* ... */ } } } /* for ( it = frame->begin(); !(it.atEnd()); ++it ) */ 

but note that this is simplified for brevity. It is necessary to consider the nested frames.

If you are interested in a full implementation, check out the git repository (work continues, November 2012).