How to use separate threads for pushbuttons in QT (like SwingWorker in Java)

[artt]

So how I need to emit signal with run() method? Rthread::run{ Lister::renderxmlsignal(); emit renderxmlsignal();}. But how to connect 2 signals with 1 slot. With 2 connect statement, but with the same slot? The signall emitting free way could be process listed to xml and save it in operative memory in another big lister Qstring variable like listed2, and just put it textview. Anyway in such method implemetation I need 2 connect statements. Unfortunately thread.start() can just return void type, no qstring, so I need to save big qstring somewhere or use signal emitting.

[anda_skoa]

So how I need to emit signal with run() method?

See comment #104

But how to connect 2 signals with 1 slot. With 2 connect statement, but with the same slot?

Yes.

Unfortunately thread.start() can just return void type, no qstring, so I need to save big qstring somewhere or use signal emitting.

QThread::run() is executed in another thread, so even if it would return something your main thread would not have access to it.

So indeed, you can either store the string and retrieve it after the thread is finished or emit it via a signal.

Cheers,
_

[artt]

I do not understand how link this 2 connect statements:
f.i. connect(thread, SIGNAL(updateText(QString)), label, SLOT(setText(QString)));
what should be (updateText(QString)) - should it be wrapper of run() or start(), why to use Qstring argument?
I do not clearly grasp the linking of signal-slot (if button-click() --> trigger the SLOT), but here I want to signal() return the whole Qstring, then SLOT take it and assign to textview. Or you mean (updateText(QString)) is just for emit signal() so it takes the Qstring?
Why I cannot just use (thread, SIGNAL(start(), textview, SLOT(setText()) and or Qstring argument is exact argument that link signal and slot?
Anyway I need use button after clicking which I settext() but I cannot use it in aforementioned example.
So if just use it -- the textview would be filled just after launching the application, but I need use it just after clicking.
So as I understand I need some intermediate variable as listed2 where I can put the results of xml processing, and then put it in Qtextedit yet in main-gui...

[anda_skoa]

I do not understand how link this 2 connect statements:
f.i. connect(thread, SIGNAL(updateText(QString)), label, SLOT(setText(QString)));

This is only one connect statement.

what should be (updateText(QString)) - should it be wrapper of run() or start()

It is a signal, it doesn't wrap anything.

why to use Qstring argument?

You want to send text from the thread to the GUI, QString is Qt's class for text.

Or you mean (updateText(QString)) is just for emit signal() so it takes the Qstring?

Yes, signals are emitted.

Why I cannot just use (thread, SIGNAL(start(), textview, SLOT(setText())

Who would have thought?
Could it be that thread does not have a start() signal?
Could it be that textview does not have a setText() slot?

Anyway I need use button after clicking which I settext() but I cannot use it in aforementioned example.

If you need to set a text when a button is clicked, create a slot that you can connect to the button's signal and call widget setters from there.

So as I understand I need some intermediate variable as listed2 where I can put the results of xml processing, and then put it in Qtextedit yet in main-gui...

I have no idea what you mean.

Cheers,
_

[artt]

Our last spin of discussion is probably the most worthless and long -- of course I need simple action triggeed by button.
As all of the others. So I see just transient variable, that got qtext variable after thread processing, and then assigning it to Qtextview in connect() statement by button. Notheing more... Despite processing xml, then assigning to variable, despite using some aditional resources as virtual memory would be justified, as I just put this variable to Qtextview in readxml() and maybe free the virtual memory in the same method.
So my SLOT(readxmlinthread()) would like as:
readxmlinthread() {
thread.start();//process to xml Qstring listed2
textview.setText(Lister::listed2);
//use destructor to free listed2 on heap;
}

[artt]

Here I defined such variable and slot method in Lister.cpp:

QList <Filewalker*> Lister::listed;
QString Lister::listed2("dddddd"); //I assigned such simple text for simple testing
...
void Lister::readthread() { //As slot function
    RThread* R=new RThread();
    R->start();
    textview->setText(Lister::listed2); //It doesnt render dddddd
    textview->setText("Lister::listed2"); //But it render "Lister::listed2" --So did I incorrectly assign listed2 to textview with setText()? 
}

QList <Filewalker*> Lister::listed;
QString Lister::listed2("dddddd"); //I assigned such simple text for simple testing
...
void Lister::readthread() { //As slot function
    RThread* R=new RThread();
    R->start();
    textview->setText(Lister::listed2); //It doesnt render dddddd
    textview->setText("Lister::listed2"); //But it render "Lister::listed2" --So did I incorrectly assign listed2 to textview with setText()? 
}

To copy to clipboard, switch view to plain text mode 

[anda_skoa]

So I see just transient variable, that got qtext variable after thread processing, and then assigning it to Qtextview in connect() statement by button

A connect doesn't assign anything.
It provides a connection between a signal and a slot.
When the signal is emitted, the slot is invoked.
If the signal carries arguments, then the slot is called with these arguments.

So my SLOT(readxmlinthread()) would like as:
readxmlinthread() {
thread.start();//process to xml Qstring listed2
textview.setText(Lister::listed2);
//use destructor to free listed2 on heap;
}

That is obviously not going to work, as the thread is running in parallel so that variable might or might not have been set at the point of reading it.
Also obviously not thread-safe.

Hence the suggetion to use a signal:
- is thread-safe
- sets the widget's value then the value has been calculated
- avoids hacks such as this static variable

Cheers,
_

[artt]

I see that it doesnt work - but I ask probably 7-8 time here - how connect Button, signal from thread with xmlprocessing results and textview it main gui? i have no suggestion as there is nessecity of transient variable.

[anda_skoa]

I see that it doesnt work - but I ask probably 7-8 time here - how connect Button, signal from thread with xmlprocessing results and textview it main gui?

So what is the problem with the examples that were already given?

Comment #7 shows how to connect a button to a slot from within the receiver class.
Comment #13 shows a connect of a button signal to a slot from outside both sender and receiver.
Comment #44 has several examples of connecting signals that carry arguments.
Comment #100 shows a declaration of a custom signal and how to use it as a cross-thread data exchange mechanism.
Comment #104 shows how to emit such a signal.

Cheers,
_

[artt]

I have looked through your references: but if signal() is just declared, not defined what is the sense of its argument.
If I declare:
signals: setuptext(Qstring);
and then emit...
How I can link void readxmldirectly() [that shapes these mega QString as the result of xml processing] to this signal?
How I can link as well button with clicked() signal??
Maybe it is impossible to realize such option -- maybe it needs some queue or some nested signal-slot connection?
As you cannot provide some blueprint, I think you have no idea too, or I am not correct -- as the task not simply connect the signal with slot, but connect signal from button with the output of thread processing to slot??
Maybe I could override in such way -- button,clicked(Qstring) and clicked is triggered when I emit signal with the thread::run() output?

[anda_skoa]

The button's clicked() signal gets connected to a slot.
The slot creates the thread instance, connects the thread's signal and starts the thread.
The thread emits the signal when it is done.

Cheers,
_