UI doesn' t update in qt app - c++

Question

In the code above uitablewidget does not update using signal and slot.
It seems as if (ui->tableWidget->setItem(0,0,newItemx);) doesn't work.
Am I doing something wrong or is there a better way to update my qtablewidget from my class B?
Class_A::Class_A(QWidget *parent):QDialog(parent),ui(new Ui::Class_A)
{
ui->setupUi(this);
}
Class_A::~Class_A()
{
delete ui;
}
void Class_A::change_TableWidget(double x,double y) // this is the public slot
{
QTableWidgetItem *newItemx = new QTableWidgetItem(QString::number(x));
ui->tableWidget->setItem(0,0,newItemx);
QTableWidgetItem *newItemy = new QTableWidgetItem(QString::number(y));
ui->tableWidget->setItem(0,0,newItemy);
}
Class_B::Class_B(QWidget *parent) :
QGLWidget(parent)
{
Class_A *t=new Class_A;
connect(this,SIGNAL(mySignal(double,double)),t,SLOT(change_TableWidget(double,double)));
}
void Class_B::mousePressEvent(QMouseEvent *event)
{
double x = event->x();
double y = event->y();
emit mySignal(x,y);
}

Answer 1

You don't have a SLOT(change_TableWidget(double,double)) - yours takes 3 doubles, not two.
You should check that connect() returned true. I like to write
if (!connect(....)) Q_ASSERT(false);
or if (!connect(....)) Q_ASSERT(!"connect");
Also, connect prints out messages to the debug output when it fails to match the signals and slots. You should look for that output.
(Or use the new Qt 5 connect(), which is all checked at compile time.)