QLibrary lib("D:\\MyPro\\MercuryAPI.dll");
if(!lib.load())
{
qDebug() << "\n Library is not loaded \n";
return false;
}
else
qDebug() << "\n Library is loaded \n";

#include <QtGui/QApplication>
#include "widget.h"
#include "widget2.h"

int main(int argc, char *argv[])
{
QApplication a(argc, argv);
Widget w;
widget2 w2;

QObject::connect(&w, SIGNAL(signalOK()), &w2, SLOT(slot()));
QObject::connect(&w2, SIGNAL(signal()), &w, SLOT(slotVisible()));

QObject::connect(&w, SIGNAL(signalCancel()), &w, SLOT(close()));

w.show();
return a.exec();
}

#include "widget.h"
#include "ui_widget.h"

Widget::Widget(QWidget *parent) :
QWidget(parent),
ui(new Ui::Widget)
{
ui->setupUi(this);
QObject::connect(ui->pushOK, SIGNAL(clicked()), this, SLOT(slotOK()));
QObject::connect(ui->pushCancel, SIGNAL(clicked()), this, SLOT(slotCancel()));
}

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

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

void Widget::slotOK()
{

emit signalOK();

}

void Widget::slotVisible()
{

close();

}

void Widget::slotCancel()
{

emit signalCancel();

}

#include "widget2.h"
#include "ui_widget2.h"

widget2::widget2(QWidget *parent) :
QWidget(parent),
ui(new Ui::widget2)
{
ui->setupUi(this);
}

widget2::~widget2()
{
delete ui;
}

void widget2::changeEvent(QEvent *e)
{
QWidget::changeEvent(e);
switch (e->type()) {
case QEvent::LanguageChange:
ui->retranslateUi(this);
break;
default:
break;
}
}

void widget2::slot()
{
show();
emit signal();
}