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I have a QTextEdit that contains a QTextDocument, which is being programatically edited using the QTextCursor interface. The document is being edited with QTextCursor::insertText().

I load the text file being edited in chunks, so the initial size of the QTextDocument might only be 20 lines even though the document is 100,000 lines. However, I want the QTextEdit scrollbar to reflect the full size of the document instead of just the 20 line document it's currently displaying.

The QTextEdit's scrollbar range is set with QScrollBar::setMaximum() which adjusts the scrollbar to the proper size on the initial opening of the file, but when QTextCursor::insertText() is called the QScrollBar's range is recalculated.

I've already tried calling QScrollBar::setMaximum() after each QTextCursor::insertText() event, but it just makes the whole UI jerky and sloppy.

Is there any way to keep the range of the QScrollBar while the QTextDocument is being modified?

Yes. You'd depend on the implementation detail. In QTextEditPrivate::init(), the following connection is made:

Q_Q(QTextEdit);
control = new QTextEditControl(q);
...
QObject::connect(control, SIGNAL(documentSizeChanged(QSizeF)), q, SLOT(_q_adjustScrollbars()))

Here, q is of the type QTextEdit* and is the Q-pointer to the API object. Thus, you'd need to disconnect this connection, and manage the scroll bars on your own:

bool isBaseOf(const QByteArray &className, const QMetaObject *mo) 
 while (mo) 
 if (mo->className() == className)
 return true;
 mo = mo->superClass();
 
 return false;


bool setScrollbarAdjustmentsEnabled(QTextEdit *ed, bool enable) 
 QObject *control = ;
 for (auto *ctl : ed->children()) 
 if (isBaseOf("QWidgetTextControl", ctl->metaObject()) 
 Q_ASSERT(!control);
 control = ctl;
 
 
 if (!control)
 return false;
 if (enable)
 return QObject::connect(control, SIGNAL(documentSizeChanged(QSizeF)), ed, SLOT(_q_adjustScrollbars()), Qt::UniqueConnection);
 else
 return QObject::disconnect(control, SIGNAL(documentSizeChanged(QSizeF)), ed, SLOT(_q_adjustScrollbars()));

Hopefully, this should be enough to prevent QTextEdit from interfering with you.

I'm using qt for python but I Think the underground is same.

1. you decide the page size valiable.(A4 = width=797,height=1023)


2. you insert Text.


3. if you insert Text,the textcursor is the bottom line on the document.


4. you get the rect.


5. you devide the rect by the pagesize.


6. If the text length 20lines are equal to 1 page, the line of 20 is the last of one page.probably,this page bottom height is 1023 if you set the height 1023. current_bottomline + cursor.height > 1023*pageheight = current_page last_bottomline + cursor.height>1023*lastpageheiht = max_page


7. you resize the textedit.(797,1023*page)



8. If you delete the texts by backspace key or delete key,you must recalculate the last botom line.(I recommend that this check is done in the KeyEvent.)QTextCursor.movePosition(QtGui.QTextCursor.End,QtGui.QTextCursor.MoveAnchor,1)




9. And,you get the cursorRect()



10. you divide the height by A4 Size unit-height.


11. if the height 102300, the page will be 100.


12. to set pagesize to 100.


13. you resize textedit resize(797,1023*page)


14. you can get textedit.verticalScrollBar()
    


15. you set the verticalScrollBar() setMaximum(the last page height)


16. You set SliderPosition by setSliderPosition(the same value or a Little difference of current textcursor y position)

I couldn't know if the scrollBar was taken from textedit.verticalScrollBar() pointer from your question.This is a Little verbose but this can be a way of solution.