QAbstractTextDocumentLayout Class Reference
[QtGui module]

void QAbstractTextDocumentLayout::documentChanged ( int position, int charsRemoved, int charsAdded )   [pure virtual protected]

This function is called whenever the contents of the document change. A change occurs when text is inserted, removed, or a combination of these two. The change is specified by position, charsRemoved, and charsAdded corresponding to the starting character position of the change, the number of characters removed from the document, and the number of characters added.

For example, when inserting the text "Hello" into an empty document, charsRemoved would be 0 and charsAdded would be 5 (the length of the string).

Replacing text is a combination of removing and inserting. For example, if the text "Hello" gets replaced by "Hi", charsRemoved would be 5 and charsAdded would be 2.

For subclasses of QAbstractTextDocumentLayout, this is the central function where a large portion of the work to lay out and position document contents is done.

For example, in a subclass that only arranges blocks of text, an implementation of this function would have to do the following:

• Determine the list of changed QTextBlock(s) using the parameters provided.
• Each QTextBlock object's corresponding QTextLayout object needs to be processed. You can access the QTextBlock's layout using the QTextBlock::layout() function. This processing should take the document's page size into consideration.
• If the total number of pages changed, the pageCountChanged() signal should be emitted.
• If the total size changed, the documentSizeChanged() signal should be emitted.
• The update() signal should be emitted to schedule a repaint of areas in the layout that require repainting.

See also QTextLayout.