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

[artt]

connect(thread, SIGNAL (update(QString)...) -- then I need to make the Qtextedit (Qlabel) field the member of Thread class -but other Qbuttons will be the Lister members - as well as the layout widget...
But it need to be composite (sorry - it should call - solid or indivisable to be more apt), how one widgets would be in one gui, the others - in another??

[anda_skoa]

connect(thread, SIGNAL (update(QString)...) -- then I need to make the Qtextedit (Qlabel) field the member of Thread class

Nope.

Cheers,
_

[artt]

So how? In updatetext() I need to use Qtextedit field, and how I use this field without Lister object creation, or I shoud create Qtextedit in Thread object - but it shoud be in GUI-thread (to avoid ASSERT failure).
I did not used sognal emitting never.

[anda_skoa]

The thread emits the signal, the widget receives it.
You connect in Lister, when you've created the thread instance, before starting it.

So the widget can either be Lister itself or one of its members.
No need to have a member in the thread.

Emitting the signal is just

emit updateText(someQStringVariable);

emit updateText(someQStringVariable);

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Cheers,
_

[artt]

How can I use QTextEdit textview in signal without creating Lister object, as it is the part of Lister class?

[anda_skoa]

You either connect to a slot of the text edit itself or to a slot in Lister and the call setter methods on the text edit from that slot.

Cheers,
_

[artt]

I cannot suggest how? Would you? Either way I need Lister->textview or the most simple Lister::textedit..

[anda_skoa]

I cannot suggest how? Would you? Either way I need Lister->textview or the most simple Lister::textedit..

Lets assume the slot is a method of Lister.
Then you can just address any member with its name.
Just as you would in Java.

Cheers,
_

[artt]

What kind of signal should be- declaration and definition; Anyway it should be connected with the button - renderdirectly (or from file) - so I need anyway the object of Lister.
So if I add signal I need Lister object - so task appear more complex - and Slot is also Lister function and need its object if non-static.

[anda_skoa]

What kind of signal should be- declaration and definition

Comment #100 has an example for a declaration.
The definition of a signal is handled by MOC, nothing to do for you.

Anyway it should be connected with the button

QPushButton has a setText slot, so that would work just like for a label.

So if I add signal I need Lister object

Not sure what you mean.
You don't need a Lister object to add a signal to the thread class.

You don't need a Lister object to connect if there is some place other than Lister that knows both the thread object and the receiver object.
But Lister should have both, so it is the best place to put the connect into.
And you already have an instance of Lister, so no new thing required.

and Slot is also Lister function

Not necessarily as you can connect to any other object that has a slot matching the signal.

However, since your target for the signal seems to change a lot (first you had a label, then a text edit, now you've asked about a button), it might be easier to just connect to a slot in Lister and handle whatever UI update from there.

Cheers,
_

[artt]

setText() is about adding the label for button itself- anyway it would not affect probably the Qtextedit area as it is the another widget. Anyway I need to use non-static variable of some class (in that case the Lister, or any other) that should be instatiated. If instantiated in some thread -- it will be out of non-GUI thread that lead to error.
What signal could do - just trigger slot reaction- or how it put textstream to created Lister textview if it needs to put inside another thread first. Could your provide workable example of it, I think it should not be difficult?

[anda_skoa]

setText() is about adding the label for button itself

Yes, correct.

Anyway I need to use non-static variable of some class (in that case the Lister, or any other) that should be instatiated.

Correct and you already have an instance of Lister.

If instantiated in some thread -- it will be out of non-GUI thread that lead to error.

Exactly, so don't do that.

What signal could do - just trigger slot reaction- or how it put textstream to created Lister textview if it needs to put inside another thread first.

I am afraid I have no idea what you mean.
What do you "need to put inside another thread first"?

Could your provide workable example of it, I think it should not be difficult?

A workable example for what?

Cheers,
_

[artt]

I need the "textview" and qlabel to assigned inside thread, in another case, I should leave as it is. Whether you propose to create separate
thread for rendering text, but Qtextedit assigned to be done outside of it. What then the sense of it? What work of such thread would do? How it would relinquish the main-gui as the asisgning should be done just there. Maybe such assigning could not lead to freezing so any sense to make new thread, despite in Java rendering of big xml files was time consuming enough?
Then why I need to use textupdate of qpushbutton?

[anda_skoa]

I need the "textview" and qlabel to assigned inside thread

No. Remember only the main thread interacts with widgets directly.

You need the thread to send data via signal and the slot puts that data onto widgets.
The given example was for text, i.e. QString.

Cheers,
_

[artt]

Lets assume that several signals could be connected to one slot -- despite it seems that it could be without signals in the whole.
We have such method:

void Lister::readxmldirectly() {
    QByteArray* ba=new QByteArray();
    QXmlStreamWriter stream(ba);
    stream.setAutoFormatting(true);
    stream.writeStartDocument();
    stream.writeStartElement("FILESYSTEM");
    foreach (Filewalker* fp, Lister::listed) {
        stream.writeStartElement("FILE");
        stream.writeStartElement("NAME"); 
      ..........
        QTextStream ReadFile(ba); (1)
 
        Lister::textview->setText(ReadFile.readAll()); (2)
}

void Lister::readxmldirectly() {
    QByteArray* ba=new QByteArray();
    QXmlStreamWriter stream(ba);
    stream.setAutoFormatting(true);
    stream.writeStartDocument();
    stream.writeStartElement("FILESYSTEM");
    foreach (Filewalker* fp, Lister::listed) {
        stream.writeStartElement("FILE");
        stream.writeStartElement("NAME"); 
      ..........
        QTextStream ReadFile(ba); (1)

        Lister::textview->setText(ReadFile.readAll()); (2)
}

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then I could put the (1) in signal processing method --signal()
then emit it, or simply put in run(), but in this case the signal() should be static one.
Then pass the (1) Qtextstream already outside of thread in SLOT of Lister
where would be the last line of above method-

Lister::textview->setText(ReadFile.readAll());

Lister::textview->setText(ReadFile.readAll());

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--If use the emit signal() --where put [emit signal()]?
Inside run()?
And it is in case if the signature of connect would be such one,

connect(f->readxml, SIGNAL(clicked()),f, SLOT(readthread()));

connect(f->readxml, SIGNAL(clicked()),f, SLOT(readthread()));

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As I need connect readxml button with Slot
--So I need put

Lister::textview->setText(ReadFile.readAll())

Lister::textview->setText(ReadFile.readAll())

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just inside (readthread())??

[anda_skoa]

Lets assume that several signals could be connected to one slot

Yes, that is possible.

despite it seems that it could be without signals in the whole.

Sure, signals are only one option of transferring data from a worker thread to the main thread.
Usually the most convenient way though.

We have such method:

void Lister::readxmldirectly() {
    QByteArray* ba=new QByteArray();
    QXmlStreamWriter stream(ba);
    stream.setAutoFormatting(true);
    stream.writeStartDocument();
    stream.writeStartElement("FILESYSTEM");
    foreach (Filewalker* fp, Lister::listed) {
        stream.writeStartElement("FILE");
        stream.writeStartElement("NAME"); 
      ..........
        QTextStream ReadFile(ba); (1)
 
        Lister::textview->setText(ReadFile.readAll()); (2)
}

void Lister::readxmldirectly() {
    QByteArray* ba=new QByteArray();
    QXmlStreamWriter stream(ba);
    stream.setAutoFormatting(true);
    stream.writeStartDocument();
    stream.writeStartElement("FILESYSTEM");
    foreach (Filewalker* fp, Lister::listed) {
        stream.writeStartElement("FILE");
        stream.writeStartElement("NAME"); 
      ..........
        QTextStream ReadFile(ba); (1)

        Lister::textview->setText(ReadFile.readAll()); (2)
}

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Assuming that the last two statements are not in the loop, why not just simply let the QXmlStreamWriter work on a QString and set that on "textview"?

Cheers,
_

[artt]

Not the first statement is the whole method. The second statement is just last line. That I wanted to put just last line out of workerthread, so assignt textstream to qtextedit in GUI-thread or convert it beforehand to Qstring and then to assign just it to qtextedit. But I cannot know if I can to return method of such big qstring in about 1.5 million lines passing it to textview.setText(...)?

[anda_skoa]

Not the first statement is the whole method. The second statement is just last line.

Ah, ok.

That I wanted to put just last line out of workerthread, so assignt textstream to qtextedit in GUI-thread or convert it beforehand to Qstring and then to assign just it to qtextedit.

Right, that would be my approach as well:
- connect thread's signal to textview's setText()
- create the QString in the worker thread
- emit string via signal

But I cannot know if I can to return method of such big qstring in about 1.5 million lines passing it to textview.setText(...)?

No better way than to try and find out

Cheers,
_

[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,
_