QLayoutPrivate issue

[gimel]

I am trying to extend the Qt example FlowLayout to include the insertWidgetAt(int position, QWidget* w) method.

I wrote (borrowed the code from QBoxLayout):

//public:
void FlowLayout::insertWidgetAt(int pos,QWidget *w){
     addChildWidget(w);
     insertItem(pos,QLayoutPrivate::createWidgetItem(this, w)); //***
     invalidate();
}
 
//private:
void FlowLayout::insertItem(int pos,QLayoutItem *item){
     itemList.insert(pos,item);
}

//public:
void FlowLayout::insertWidgetAt(int pos,QWidget *w){
     addChildWidget(w);
     insertItem(pos,QLayoutPrivate::createWidgetItem(this, w)); //***
     invalidate();
}

//private:
void FlowLayout::insertItem(int pos,QLayoutItem *item){
     itemList.insert(pos,item);
}

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At the line marked with //***, gcc gives "incomplete type `QLayoutPrivate' used in nested name specifier" error. What should I do to implement the method?