slot parameter for QMetaObject::invokeMethod - c++

Question

Playing with QMetaObject::invokeMethod method :
#include "mainwindow.h"
#include "ui_mainwindow.h"
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
}
MainWindow::~MainWindow()
{
delete ui;
}
void MainWindow::setText( int value)
{
QString s = QString::number(value);
ui->textEdit->setText(s);
}
void MainWindow::on_pushButton_clicked()
{
QGenericArgument genericArg = Q_ARG(int, 321);
bool inv = QMetaObject::invokeMethod( this,"setText",Qt::BlockingQueuedConnection, genericArg);
qDebug("inv = %d\n", inv);
}
QMetaObject::invokeMethod returns false.
I'm not sure regarding slot "setText". I took it from function name and I suppose it might be related. Where I can find list of slots at all? Should I create special slot for "setText"?
Maybe it is related to fact I run it from the same thread?
UPD:
I have added public slot instead of public method:
namespace Ui {
class MainWindow;
}
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = 0);
~MainWindow();
//void setText( int value);
private slots:
void on_pushButton_clicked();
public slots:
void setText(int value);
private:
Ui::MainWindow *ui;
};
And this helped, but why I'm getting 0 in setText value ?

Answer 1

Your button-event is handled by the event loop that owns the MainWindow object and this same object also contains the method you wish to invoke (setText()). That means that caller and callee (or signal and slot) in your case live on the same thread, and you must not use Qt::BlockingQueuedConnection! To quote the manual: Using this connection type to communicate between objects in the same thread will lead to deadlocks.
If you intent to do processing in your on_pushButton_clicked() after the setText() method has finished, use a Qt::DirectConnection instead, then your setText() will be called as if it was a simple function, and control returns to your clicked() function after setText() finished.
If you intent to finish processing all code in your on_pushButton_clicked() before processing of the setText() function starts, use a Qt::QueuedConnection.
If you wish to execute setText() in parallel to on_pushButton_clicked(), then move your setText() method to another object (which is owned by another thread). Only in this scenario a Qt::BlockingQueuedConnection makes sense.