Qt,how does ProcessState enum works - qt

Question

I don't under stand how to use the ProcessState enums. According to documentation, the ProcessState enum can have the following values:
QProcess::NotRunning- 0 - The process is not running.
QProcess::Starting- -1-The process is starting, but the program has not yet been invoked.
QProcess::Running -2 -The process is running and is ready for reading and writing.
How would I use them?

Answer 1

What you refer to are not functions, simply values. You could assign them to an integer and output its value:
int val = QProcess::Starting;
qDebug() << "the value of QProcess::Starting is" << val;
To check the state of a process, you could do:
QProcess *process;
....
if (process->state() == QProcess::Running) // do something with a running process
Of course, when it comes to a QProcess, you really need to be handling signals that the process emits as it changes state. You do not want to do any sort of busy-waiting, and I should discourage the use of any Qt function called waitFor.... Those functions cause the event loop to be re-entered, and potentially to re-enter your code that you never realized could be re-entered. It's a Pandora's box you do not want to open. About the only valid use of wait-style functions is to wait for QThreads that have been quit() to finish before you return from the main() function.

Answer 2

You can have states for the processes to be run. You can then connect your slot to the state changed signal, even in QML if needed, and act accordingly. Also, not that there is no such a thing as "enum function". It is just a simple enumeration that basically the state "property" holds. You can query and set it the usual way. You can see the documentation for those methods below.
http://qt-project.org/doc/qt-5.0/qtcore/qprocess.html#state
http://qt-project.org/doc/qt-5.0/qtcore/qprocess.html#setProcessState
This looks like a generic Qt examples as your question is, but here you go:
myclass.h
class MyClass : QObject
{
Q_OBJECT
public:
explicit MyClass(QObject *parent);
public Q_SLOTS:
void handleProcessStateChanged(QProcess::ProcessState newProcessState);
....
}
myclass.cpp
...
MyClass::MyClass(QObject *parent)
: QObject(parent)
{
}
MyClass::myProcessInvokeMethod()
{
connect(myprocess, SIGNAL(stateChanged(QProcess::ProcessState), this, SLOT(handleStateChange(QProcess::ProcessState)));
myprocess.start(myprogram, myarguments);
....
}
void MyClass::handleProcessStateChange(QProcess::ProcessState newProcessState)
{
switch (newProcessState) {
case QProcess::NotRunning:
qDebug() << "Here goes the handler code when the process is not yet running";
break;
case QProcess::Starting:
qDebug() << "Here goes the handler code when the process is starting";
break;
case QProcess::Running:
qDebug() << "Here goes the handler code when the process is running";
break;
}
}
...