Getting access to SeekSlider from another class

Hello.
I'm writing a litte music-player based on Qt and Phonon.
Im using a double-linked list (writed by myself) to storage a data and information. First class, File, storage information about opened files:

Code:

#include "file.h"
 
//Phonon::MediaObject *mediaObject;
//Phonon::AudioOutput *audioOutput;
 
File::File()
{
    this->next = 0;
    this->prev = 0;
    this->path_to_file = "";
    this->fileName = "";
    this->title = "";
}
 
void File::setPath(QString path)
{
    this->path_to_file = path;
}
 
QString File::returnPath()
{
    return this->path_to_file;
}
 
void File::playFile()
{
    this->mediaObject = new Phonon::MediaObject(this);
    this->mediaObject->setCurrentSource(this->returnPath());
    this->audioOutput = new Phonon::AudioOutput(Phonon::MusicCategory,this);
    Phonon::Path path = Phonon::createPath(this->mediaObject,this->audioOutput);
    this->mediaObject->play();
}
 
void File::stopFile()
{
    this->mediaObject->stop();
}
 
 
void File::setFileName(QString path)
{
    int n = 0; QString temp = "";
    for(int i=0;i<path.length();i++)
    {
        if (path[i] == '/')
            n = i+1;
    }
    for(int i=n;i<path.length();i++)
        temp.append(path[i]);
    this->fileName = temp;
}
 
QString File::returnFileName()
{
    return this->fileName;
}
 
File *File::Copy(File &f)
{
    File * temp = new File();
    temp->setFileName(f.returnFileName());
    temp->setPath(f.returnPath());
    temp->next = f.next;
    temp->prev = f.prev;
    return temp;
}

And second class it's double-linked list.

I want to make a seekslider, but I have a little problem. I'm using mediaObject not in MainWindow, but in another class.
Something like this doesnt work (in MainWindow):

Code:

ss->setMediaObject(playlist->ReturnX(i)->mediaObject);

I also can't make a function i File class that return a mediaObject.

Someone can help me how to resolve this problem??