Another.cpp

TextProxy *tp = new GraphicsTextProxy(blafoo);
/* edit: missed the new */

/* 
 * this should call GraphicsTextProxy::setText 
 */
tp->setText("random");
/* 
 *but it calls TextProxy::setText 
 * WHY? And how to change it?
 */

GraphicsTextProxy.cpp

#include "GraphicsTextProxy.h"

GraphicsTextProxy::GraphicsTextProxy(myGraphicsTextItem *item)
{
    //...
}

void GraphicsTextProxy::setText(const QString &str)
{
    //...
}

const QString GraphicsTextProxy::getText()
{
    //...
}

GraphicsTextProxy.h

#ifndef GRAPHICSTEXTPROXY_H
#define GRAPHICSTEXTPROXY_H

#include "TextProxy.h"
#include "myGraphicsTextItem.h"

class GraphicsTextProxy : public TextProxy
{
public:
    GraphicsTextProxy(myGraphicsTextItem *item);
    void setText(const QString &str);
    const QString getText();

private:
    myGraphicsTextItem *item;
};

#endif // GRAPHICSTEXTPROXY_H

TextProxy.h

#ifndef TEXTPROXY_H
#define TEXTPROXY_H

#include <QString>

class TextProxy
{
    public:
    virtual void setText(const QString &str) {};
    virtual const QString getText() {};
};

#endif // TEXTPROXY_H