QSocketNotifier always fire once on startup

[sharethl]

Hi,

The notifier is used to monitor a GPIO, who's edge = falling.
After setting up, it immediately fire a signal. but I haven't press that button yet.

What could be the cause?

@MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{

ui->setupUi(this);

QFile edge_file("/sys/class/gpio/gpio19/edge");
if (!edge_file.open(QIODevice::WriteOnly)) {
    return;
}
QTextStream out_edge(&edge_file);
out_edge << "falling";
edge_file.close();

//http://meecom.blogspot.com/2014/06/qt-beagle-bb-gpio-tcp-client.html
keyValueFile.setFileName("/sys/class/gpio/gpio19/value");
keyValueFile.open(QFile::ReadOnly);
_gpioNotifier = new QSocketNotifier(keyValueFile.handle(), QSocketNotifier::Exception);

connect(_gpioNotifier, SIGNAL(activated(int)), this, SLOT(readyRead(int)));

}
/**

• @brief MainWindow::readyRead
• Need read values to prevent reentry.
• @param value
  */
  void MainWindow::readyRead(int value)
  {
  QByteArray line;
  keyValueFile.seek(0);
  line = keyValueFile.readAll();
  qDebug() << line;

}@

Thanks