Qt - children set font breaks positioning

Okay, so I've started making a game using Qt so that I can learn both Qt and C++ at the same time :D However, I'm stuck with an issue at the moment.

I'm trying to make a textbox using a QGraphicsRectItem as a container (parent), and a QGraphicsTextItem as the text itself (child). The problem I'm facing is the child's relative position to the parent. If I set a font on the QGraphicsTextItem, the positioning will be completely wrong, and it will flow outside of the container for that matter.

TextBox.h:

#ifndef TEXTBOX_H
#define TEXTBOX_H

#include <QGraphicsTextItem>
#include <QGraphicsRectItem>
#include <QTextCursor>
#include <QObject>

#include <qDebug>
class TextBox: public QObject, public QGraphicsRectItem {
    Q_OBJECT
public:
    TextBox(QString text, QGraphicsItem* parent=NULL);

    void mousePressEvent(QGraphicsSceneMouseEvent *event);

    QString getText();

    QGraphicsTextItem* playerText;
};

#endif // TEXTBOX_H

TextBox.cpp

#include "TextBox.h"

TextBox::TextBox(QString text, QGraphicsItem* parent): QGraphicsRectItem(parent) {
// Draw the textbox
    setRect(0,0,400,100);
    QBrush brush;
    brush.setStyle(Qt::SolidPattern);
    brush.setColor(QColor(157, 116, 86, 255));
    setBrush(brush);

// Draw the text
    playerText = new QGraphicsTextItem(text, this);
    int xPos = rect().width() / 2 - playerText->boundingRect().width() / 2;
    int yPos = rect().height() / 2 - playerText->boundingRect().height() / 2;
    playerText->setPos(xPos,yPos);
}

void TextBox::mousePressEvent(QGraphicsSceneMouseEvent *event) {
    this->playerText->setTextInteractionFlags(Qt::TextEditorInteraction);
}

Game.cpp (where the code for creating the object and such is located - only included the relevant part):

// Create the playername textbox
    for(int i = 0; i < players; i++) {
        TextBox* textBox = new TextBox("Player 1");
        textBox->playerText->setFont(QFont("Times", 20));
        textBox->playerText->setFlags(QGraphicsItem::ItemIgnoresTransformations);
        scene->addItem(textBox);
    }

Using the default font & size for the QGraphicsTextItem:

Setting a font & size for the QGraphicsTextItem:

The problem, as you may see, is that when I set a font and a size, the text is no longer in the center of the parent element. (Please do not unleash hell on me for bad code, I'm very new to both Qt and C++, and I'm doing this for learning purposes only).

You are calling the boundingRect() method in the constructor, so the position is set before the font is set to it's final value. If you either make a method to set the position and call it after setting the font or set the font before setting the position in the constructor it should work.