[SOLVED]In detial how to using SIGNAL/SOLT to interaction with UI widget in other CPP file？

[Season02]

I have creat a Qt gui project，in .ui file had insert some widget like TEXTBOX and LISTWIDGET，then I want interaction with them in other .cpp file.
And the better way to do this is using SIGNAL/SLOT.Though I already studied it,i still can`t achiece the goal.

below are my code:

in mainwindow.h:

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();

public slots:
    void additem(const QString& text);

private:
    Ui::MainWindow *ui;
};

#endif // MAINWINDOW_H

in mainwindow.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include "testclass.h"

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

    testclass t;
}

void MainWindow::additem(const QString& text)
{
    ui->listWidget->addItem(text);
}

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

in testclass.h

#ifndef TESTCLASS_H
#define TESTCLASS_H

#include <QObject>
#include <mainwindow.h>

class testclass : public QObject
{
    Q_OBJECT
public:
    explicit testclass(QObject *parent = 0);
    ~testclass();

signals:
    void add(const QString& text);

public slots:

private:
    MainWindow *mainwindow;
};

#endif // TESTCLASS_H

in testclass.cpp

#include "testclass.h"

testclass::testclass(QObject *parent) : QObject(parent)
{
    connect(this,SIGNAL(add(const QString&)),mainwindow,SLOT(additem(const QString&)));
    emit add("simulation");
}

testclass::~testclass()
{

}

Where are wrong?How can I fix it?
Any suggestion will be very appreciated.

[Jakob]

@Season02 I believe your chances of receiving a response will probably be better if you type in English

[Season02]

@Jakob Thank you,I will try later.

[Season02]

This post is deleted!

[Season02]

I still need study a lot about SIGNAL/SLOT.

[jiancaiyang]

SIGNAL和SLOT在Qt中是非常重要的内容。
反映到Qt Quick，则是signal和signal handler。