C++11 thread in qt 5 - c++

Question

//MainWindow.cpp
void MainWindow::threadedFunction()
{
myDialog = new MyDialogs(list,processList,this);
myDialog->show();
}
void MainWindow::createNewDialog()
{
getProcesses();
//threadedFunction(); //This works fine.
std::thread tx = std::thread(&MainWindow::threadedFunction,this);
tx.join();
}
//MyDialog.cpp
MyDialogs::MyDialogs(QList<int> lists,QStringList list,QObject *parent):QDialog(0)
{
QVBoxLayout *toplay = new QVBoxLayout(this);
listWidget = new QListWidget(this);
x<<list;
l<<lists;
listWidget->addItems(x);
toplay->addWidget(listWidget);
connect(listWidget,SIGNAL(doubleClicked(QModelIndex)),
this,SLOT(getProcessString(QModelIndex)));
}
void MyDialogs::getProcessString(QModelIndex index)
{
selectedProcessString = index.data().toString();
rowIndex = index.row();
}
Already set in pro file.
CONFIG += c++11
when I call threadedFunction directly the code works fine.
But the above mentioned code gives me runtime error.
If I use only qDebug statements in threadedFunction and remove myDialog code, the code runs fine even with the threads. What is the problem? I am using Qt5 with MingW 4.9.1 32bit. And I do not have visual studio installed.

Answer 1

The problem is that you're trying to create a UI object outside the GUI thread. I'm assuming your main function instantiates a QApplication object which starts your event loop. This thread is your one and only GUI thread. I'm guessing your GUI thread is the thread which is creating the thread that is trying instantiate the QListWidget.
If my assumptions are correct then you need to create the QListWidget in the main/GUI thread and then call your thread function. I can't say what you should do in your thread function since I'm not sure what you want to do but there are multiple ways to handle it.
You may want to look at QThread. That class will allow you to use signals and slots, which may make things easier for you. You can use traditional threading constructs (e.g., mutex , wait conditions, etc.) and shared state. There are also ways to post events which go through the message loop (i.e. get sent back into the main/GUI thread).