QFutureWatcher signal not working

[saeid0034]

Hi, Im trying to use QtConcurrent::run to run one of my function in another thread
I use this code for doing this

int getID(const char * str)
{
	DWORD ID = 0;
	while (!PID)
	{
		ID = example(str);
		Sleep(30);
	}
	return ID;
}

void mainw::on_pushButton_clicked() //Start Injector and game
{
	const char* szP = "something";

	QFutureWatcher<int> watcher;
	connect(&watcher, &QFutureWatcher<int>::finished, this, &mainw::After_PID);

	QThreadPool pool;
	QFuture<int> future = QtConcurrent::run(getID, szP);
	watcher.setFuture(future);
	//QString result = future.result();

//after that I also want to get output of getProcID return in this function too
int mainw::After_PID(int pid)
{
	if (pid != 0)
	{
		ui.textBrowser->append("Process Founded: " + pid);
                //some other code
	}
	return 0;
}

my code have lots of problem, but my main problem is why watcher signal doesn't work?
(for test I remove all arg from After_PID and tried to simple only print a text for test, but its wont work)
so I want to know

1. how can I get watcher signal to work
2. how can I get getID return value in After_PID

[SGaist]

No, you need to only create it once, in the constructor. Giving it a parent means that it will be destroyed alongside its parent however you will still create new objects every time and thus fill the memory until the parent destruction.

[SGaist]

Hi,

There's no signal because your watcher lifetime ends with the end of the method it's created in.

[saeid0034]

@SGaist said in QFutureWatcher signal not working:

Hi,

There's no signal because your watcher lifetime ends with the end of the method it's created in.

thank you for fast answer, so you saying I need to declare it some where else? (maybe global in cpp?
and one other thing, how can I get return of getID (maybe declare both watcher and future outside of this method? but where is best place and what is best way to do it?)

[AnneRanch]

@saeid0034 Take a look at my posts.

I am following this tutorial

https://www.bogotobogo.com/Qt/Qt5_QtConcurrent_QFutureWatcher_QProgressDialog_map.php

which covers in principle using several Qt classes to accomplish the "delay".
The tutorial is very sketchy, it does not explain well what is going on ( in sequence) and assumes much. There are few unpublished "default" values in use.

The tutorial is OK but it needs to be implemented very carefully- step by step - also due to few time issues.

[jsulm]

@saeid0034 said in QFutureWatcher signal not working:

maybe global in cpp

Not global, but as member variable in your mainw class.

[saeid0034]

@jsulm said in QFutureWatcher signal not working:

@saeid0034 said in QFutureWatcher signal not working:

maybe global in cpp

Not global, but as member variable in your mainw class.

thank you
I use this code
in mainw header file

class mainw : public QMainWindow
{
    Q_OBJECT

public:
    mainw(QWidget *parent = Q_NULLPTR);    

private slots:
    void on_pushButton_3_clicked();
    void load_change(int index);
    void on_pushButton_clicked();
    int After_PID();

private:
    Ui::mainw ui;
    QFutureWatcher<int> *watcher;
    QFuture<int> *future;
};

and in mainw cpp

void mainw::on_pushButton_clicked() //Start Injector and game
{
	const char* szP = "something";

	watcher = new QFutureWatcher<int>;
	future = new QFuture<int>;
	
	connect(watcher, &QFutureWatcher<int>::finished, this, &InjectorGUI::After_PID);
	connect(watcher, &QFutureWatcher<int>::finished, watcher, &QFutureWatcher<int>::deleteLater);

	QThreadPool pool;
	QFuture<int> future = QtConcurrent::run(getProcID, szProc);
	watcher->setFuture(future);
	//QString result = future.result();
}

now its working and after receive finished signal After_PID opened.
thanks about that
know only thing I want to know is how can I get out put in After_PID?
-edit-
never mind after read qfuturewatcher document i find out I can use watcher->result();

[SGaist]

Note that you are now leaking QFutureWatcher objects each time you call that function.

There's no need to recreate it each time.

[saeid0034]

@SGaist said in QFutureWatcher signal not working:

Note that you are now leaking QFutureWatcher objects each time you call that function.

There's no need to recreate it each time.

thank you, so I need to add QFutureWatcher<int> *watcher = new QFutureWatcher<int>(this); instead of QFutureWatcher<int> *watcher; to header and remove watcher = new QFutureWatcher<int>; from source? right

[SGaist]

No, you need to only create it once, in the constructor. Giving it a parent means that it will be destroyed alongside its parent however you will still create new objects every time and thus fill the memory until the parent destruction.