when the window of QFileDialog::getOpenFileName opening, the program has unexpected finished - c++

Question

I'm writing a simple Qt application to test multi-threading (something I am also completely new to).I made a QApplication to manage the GUI,then I write a class VisionApp that contains the class MainWindow which is a subclass of QMainWindow.
In the MainWindow class,I write a function void MainWindow::getfromfilevd() which is connected to the button using this:
QObject::connect(ui->FileVdButton,SIGNAL(clicked()),this,SLOT(getfromfilevd()));
Then I want to read a image from file by using QFileDialog::getOpenFileName,my code is here:
void MainWindow::getfromfilevd()
{
//mutex.lock();
from_imgorvd = true;
QString fileName = QFileDialog::getOpenFileName(this, tr("Open Image"),"", tr("Image Files (*.png *.jpg *.bmp *.xpm)"));
if(fileName.isEmpty()) {
cv::Mat image;
image = cv::imread(fileName.toUtf8().constData(), CV_LOAD_IMAGE_COLOR);
mutex.lock();
Mat_Img = image.clone();
mutex.unlock();
}
}
however,every time I click the button ,the window of QFileDialog opened but it is blank,then my program finished unexpected.
when I use this code:
void MainWindow::getfromfilevd()
{
from_imgorvd = true;
cv::Mat image;
image = cv::imread("/home/somnus/Picture/mouse.jpg", CV_LOAD_IMAGE_COLOR);
if(! image.data) {
std::cout << "Could not open or find the image" << std::endl ;
}
else {
mutex.lock();
Mat_Img = image.clone();
mutex.unlock();
}
}
It works well.
I am really wonder which mistake I take...
Hope for your help

Answer 1

It should be like this, !fileName.isEmpty() in stead of fileName.isEmpty() because you need to load image when the file name is not empty not the opposite.