基于QT的窗口切换问题

我设计多个窗口，然后切换。问题现象是点击按钮后总是每次出现两个相同窗口，而不是只有一个。窗口界面有QWidget类，也有Dialog类。代码如下：
main.cpp

 #include "widget_login.h"
//#include "mainmenu.h"
#include <QApplication>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    Widget_Login w;

    w.move(200, 200);
    w.show();

    return a.exec();
}

登录界面widget_login.h

 #include <QWidget>

namespace Ui {
class Widget_Login;
}

class Widget_Login : public QWidget
{
    Q_OBJECT

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

private slots:
    void on_pushButton_clicked();

private:
    Ui::Widget_Login *ui;

};

#endif // WIDGET_LOGIN_H

widget_login.cpp

 #include "widget_login.h"
#include "ui_widget_login.h"
#include "dialog.h"
#include "mainmenu.h"
#include <iostream>
#include <fstream>

Widget_Login::Widget_Login(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::Widget_Login)
{
    ui->setupUi(this);
    connect(ui->pushButton, SIGNAL(clicked()), this, SLOT(on_pushButton_clicked()));
}

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

void Widget_Login::on_pushButton_clicked()
{
     Mainmenu *menu = new Mainmenu();

   this->close();
   menu->show();

}

主界面mainmenu.h

 #ifndef MAINMENU_H
#define MAINMENU_H

#include <QWidget>
#include "oper_window.h"

namespace Ui {
class Mainmenu;
}

class Mainmenu : public QWidget
{
    Q_OBJECT

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

private slots:

    void on_pushButton_SET_clicked();

    void on_pushButton_CHECK_clicked();

    void on_pushButton_OPERATION_clicked();

    void on_pushButton_REPLAY_clicked();

private:
    Ui::Mainmenu *ui;

};


#endif // MAINMENU_H

mainmenu.cpp

 #include "mainmenu.h"
#include "ui_mainmenu.h"
#include "widget_login.h"


Mainmenu::Mainmenu(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::Mainmenu)
{
    ui->setupUi(this);
    connect(ui->pushButton_SET, SIGNAL(clicked()), this, SLOT(on_pushButton_SET_clicked()));
    connect(ui->pushButton_CHECK, SIGNAL(clicked()), this, SLOT(on_pushButton_CHECK_clicked()));
    connect(ui->pushButton_OPERATION, SIGNAL(clicked()), this, SLOT(on_pushButton_OPERATION_clicked()));
    connect(ui->pushButton_REPLAY, SIGNAL(clicked()), this, SLOT(on_pushButton_REPLAY_clicked()));
}

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

void Mainmenu::on_pushButton_SET_clicked()
{
    Widget_Login *wi = new Widget_Login;
    this->close();
    wi->show();

}

void Mainmenu::on_pushButton_CHECK_clicked()
{

}

void Mainmenu::on_pushButton_OPERATION_clicked()
{

}

void Mainmenu::on_pushButton_REPLAY_clicked()
{

}

参考QT实现多窗口切换
http://blog.csdn.net/wc7620awjh/article/details/8574131