using QThreads, but i cant access a method of another class

[Tio]

hello everyone
i am new here, so if i've made something wrong, my apologizes ^^
Plus, i dont speak english a very well, so, i am sorry for wrong write =P
well...i have a problem.
I am using the QThreads to launch some threads. Basicaly, i have 2 classes: MainWindow, which is responsible for the window, and MyThread, for one thread.
I am going a very well, launch a thread and every else. But now, i need access some resources of the MainWindow from the MyThread. Actually, i have on the window a lcdNumber, which must be refreshed every number found in the thread. Someone knows how to make it?
here is the code (comments is in portuguese, my language, didnt mind =P):

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QThread>
#include "mythread.h"
 
 
int num = 1;
int num2 = 1000000;
int cont = 0;
 
int MyThread::primo(int n){
   int i;
 
   if( n == 1 ) return 0; // por definicao...
 
   for(i=2; i*i <= n;i++){
       if (n % i == 0) return 0; // NAO eh primo
   }
 
   return 1; // EH primo
}
 
MyThread::MyThread(QObject *parent, int num, int num2)
: QThread(parent)
{
    this->num = num;
    this->num2 = num2;
}
 
void MyThread::run()
{
        qDebug() << "Executing a new independant thread, GUI is NOT blocked";
 
        int i;
        cont = 0;
 
        for(i=num; i<num2; i++){
            if(primo(i) == 1)   cont++;  //every time that find it, must refresh the lcdNumber <--------
        }
 
        qDebug() << "Encontrados:" << cont;
 
        //exec();
}
 
int MyThread::retorno(){
    return cont;
}
 
MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
 
    QString temp;
    temp.setNum(num);
    ui->lineEdit->setText(temp);
 
    temp.setNum(num2);
    ui->lineEdit_2->setText(temp);
}
 
MainWindow::~MainWindow()
{
    delete ui;
}
 
void MainWindow::changeEvent(QEvent *e)
{
    QMainWindow::changeEvent(e);
    switch (e->type()) {
    case QEvent::LanguageChange:
        ui->retranslateUi(this);
        break;
    default:
        break;
    }
}
 
void MainWindow::on_inicio_clicked()  //button to start thread
{
    QString txt;
    txt = ui->lineEdit->text();
    num = txt.toInt();
    txt = ui->lineEdit_2->text();
    num2 = txt.toInt();
    lancaThread();
}
 
void MainWindow::on_fim_clicked() //button to terminate thread, if user needs
{
    thread->terminate();
    qDebug() << "Operacao cancelada";
}
 
void MainWindow::lancaThread()
{
    int res = 0;
        // create new thread (on heap) and start it
        thread = new MyThread(this, num, num2);
 
        thread->start(); // after this, thread's run() method starts
 
        qDebug() << "Feito";
        ui->lcdNumber->display(res);
}

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QThread>
#include "mythread.h"


int num = 1;
int num2 = 1000000;
int cont = 0;

int MyThread::primo(int n){
   int i;

   if( n == 1 ) return 0; // por definicao...

   for(i=2; i*i <= n;i++){
       if (n % i == 0) return 0; // NAO eh primo
   }
   
   return 1; // EH primo
}

MyThread::MyThread(QObject *parent, int num, int num2)
: QThread(parent)
{
    this->num = num;
    this->num2 = num2;
}

void MyThread::run()
{
        qDebug() << "Executing a new independant thread, GUI is NOT blocked";

        int i;
        cont = 0;

        for(i=num; i<num2; i++){
            if(primo(i) == 1)   cont++;  //every time that find it, must refresh the lcdNumber <--------
        }

        qDebug() << "Encontrados:" << cont;

        //exec();
}

int MyThread::retorno(){
    return cont;
}

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);

    QString temp;
    temp.setNum(num);
    ui->lineEdit->setText(temp);

    temp.setNum(num2);
    ui->lineEdit_2->setText(temp);
}

MainWindow::~MainWindow()
{
    delete ui;
}

void MainWindow::changeEvent(QEvent *e)
{
    QMainWindow::changeEvent(e);
    switch (e->type()) {
    case QEvent::LanguageChange:
        ui->retranslateUi(this);
        break;
    default:
        break;
    }
}

void MainWindow::on_inicio_clicked()  //button to start thread
{
    QString txt;
    txt = ui->lineEdit->text();
    num = txt.toInt();
    txt = ui->lineEdit_2->text();
    num2 = txt.toInt();
    lancaThread();
}

void MainWindow::on_fim_clicked() //button to terminate thread, if user needs
{
    thread->terminate();
    qDebug() << "Operacao cancelada";
}

void MainWindow::lancaThread()
{
    int res = 0;
        // create new thread (on heap) and start it
        thread = new MyThread(this, num, num2);

        thread->start(); // after this, thread's run() method starts

        qDebug() << "Feito";
        ui->lcdNumber->display(res);
}

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the last line is, basically, what i need to do up there. The "ui" is public, but i cant access. ive tried to use:
MainWindow::ui->lcdNumber->display(anumber);
but didnt work...
if someone could help me, i will be very grateful ^^
if needs more information, just ask =D
and sorry for anything