Clone QTextDocument Subclass

Question

I have a subclass of QTextDocument that overrides QTextDocument::loadResource(int type, const QUrl &name).

I want to clone it.

Ideas ?

Answer 1

You can't use QTextDocument::clone for that. Neither can you reimplement it because it's not virtual. You should create another clone method (you can name it clone but I'd give it another name to avoid confusion) and implement cloning yourself. You can use toHtml and setHtml to copy content from one object to another:

MyTextDocument* MyTextDocument::my_clone(QObject * parent = 0) {
  MyTextDocument* other = new MyTextDocument(parent);
  other->setHtml(toHtml());
  return other;
}

There are however many other properties that should be copied. See how QTextDocument::clone method is implemented:

QTextDocument *QTextDocument::clone(QObject *parent) const
{
    Q_D(const QTextDocument);
    QTextDocument *doc = new QTextDocument(parent);
    QTextCursor(doc).insertFragment(QTextDocumentFragment(this));
    doc->rootFrame()->setFrameFormat(rootFrame()->frameFormat());
    QTextDocumentPrivate *priv = doc->d_func();
    priv->title = d->title;
    priv->url = d->url;
    priv->pageSize = d->pageSize;
    priv->indentWidth = d->indentWidth;
    priv->defaultTextOption = d->defaultTextOption;
    priv->setDefaultFont(d->defaultFont());
    priv->resources = d->resources;
    priv->cachedResources.clear();
#ifndef QT_NO_CSSPARSER
    priv->defaultStyleSheet = d->defaultStyleSheet;
    priv->parsedDefaultStyleSheet = d->parsedDefaultStyleSheet;
#endif
    return doc;
}

If these properties are important to you, you need to copy them manually in your my_clone implementation. You can're use QTextDocumentPrivate class because it's internal. So you can't just copy default implementation. But there is a normal way to set each of listed properties in the API.

Be aware of forward compability issues. If new properties appeared in newer Qt versions, your implementation will not copy them in opposite to default clone implementation. That could be a problem so this approach is not perfect.