Intermediate user
Re: How to use separate threads for pushbuttons in QT (like SwingWorker in Java)
"You cannot define a static variable inside a constructor.
A static variable is always defined with its type and fully qualified classname and, optionally, a default value."
--Yes I will see it later in my Qt creator, as the static Qlist <Filewalker> listed definition was the first issue on this Qt project
--How it was simplier in java - I have just one class Filewalker, and it worked.
Administrator
Re: How to use separate threads for pushbuttons in QT (like SwingWorker in Java)
The same symbol rules apply in C++ as well, a class name can only be used once.
You need a different package (Java) or namespace (C++) to use a class name again.
Cheers,
_
Intermediate user
Re: How to use separate threads for pushbuttons in QT (like SwingWorker in Java)
I do not understand what you mean under using class name again (need new namespace). But I defined static variable (widget) - but due to it I got such error (as it is static widget definition) --
"QWidget: Must construct a QApplication before a QPaintDevice" -
as I have read about it on this forum it is because the static variable (textview) appear before the application so as I
understand before Lister (f) object with other widgets, and due to global feature of static widget it appears that it is "physically" disconnected with other widgets (that is indside window-qwidget). So probably it is unreal to use static widget in such case, and the advice to delete inheritance on Qwidget is unreal also. So just to make it non-static probably...
Despite this issue is not the main just using non-static SLOT-function in threadwarapper SLOT, that needs the static slot inside run(), that in turn nessesiate the static variable(widget).
So is it possibel to use static widget?
Or not create Lister object inside run(), but call its non-static SLot-function?
Administrator
Re: How to use separate threads for pushbuttons in QT (like SwingWorker in Java)
You wrote that in Java there would only be one FileWalker class. That is the same in C++, class names need to be unique.Originally Posted by artt
Good point, another very good reason not to do static objects.
There is no reason whatsoever to call a static method from inside run(),
I have lost track of what Lister is, but you seem to try to shoe-horn to things into one class.
You need
- a class that the application works with, that provides a slot that asks for user input, creates a thread, runs the thread and collects the result
- a thread that runs the directory traversal
If you want you can of course split the thread in two classes, the thread itself and a class that implements the directory traversal.
There is no static required in any of this.
Cheers,
_
Intermediate user
Re: How to use separate threads for pushbuttons in QT (like SwingWorker in Java)
ASSERT failure in QWidget: "Widgets must be created in the GUI thread." - here I got such error when placing non-static method in threadwrapper SLOT - it seems the same as with Qdialog (that I can find solution or absolve using of it) - it is due exactly to non-static method that uses non-static Qtextedit textview. That is why if it is also insolubilitable issue - I can set back using such non-static method is threads -that probably is affordable here. I use "textview" in readfromxmlfile and renderingdirectly xml to Qxtextedit, so it should not be very time consuming work (in Qt it seems to be faster then in Java, despite I did not tried it for the whole disk), and clearing textedit - so I could leave it in Gui-thread, as well the filenamesearch method that exploit another Qwidget(Qlabel) for the rendering finded result so I laso could not allow to use it as static.
Anyway I will refer here for the whole code so the solution could be proposed - f.e. with signals, despite the signals are buttons in my case.
Administrator
Re: How to use separate threads for pushbuttons in QT (like SwingWorker in Java)
As the error clearly indicates you are trying to create a widget from a thread that is not the main thread.
Whether that code is in a static or non-static method does not matter a bit.
This has obviously nothing to do with static vs non-static.
Cheers,
_
Intermediate user
Re: How to use separate threads for pushbuttons in QT (like SwingWorker in Java)
No, this error appears exactly here where I use non-static method in qthread::run(), as the static methods such as walk() and writexmlfile() that do not use Qwidgets works as in thread as without it - but walk() in GUI-thread freeze extremely, so thread is nessesary there anyway. If turn back to my first topic on forum about Swingworker analogue in Qt, that in Java swingworker is used for background processes such as traversing, but probably the assigning the text (despite very large) to Qtextedit is not so one, so the issue could be solved in manner not using threads for rendeing..
here is whole code:http://s000.tinyupload.com/?file_id=...85004786237054
Administrator
Re: How to use separate threads for pushbuttons in QT (like SwingWorker in Java)
No sorry.
It happens because it is called from QThread::run(), not because the method is non-static.
And the same would work in C++ as well.
This has been explained before: UI can only be interacted with from the main thread.
You worker thread either emits data as it goes and the a in the main thread handles it, or it just runs and you handle the result once it has completed its task.
- Lister is your main class, it handles the user interaction
- don't create instances of Lister in threads
* it is a widget
* it deals with the user interaction
* you already have an instance of Lister
- don't call any methods of Lister in the threads
- put code that you want the threads to execute into the thread classes
Cheers,
_
Intermediate user
Re: How to use separate threads for pushbuttons in QT (like SwingWorker in Java)
1. It happens because it is called from QThread::run(), not because the method is non-static
2. - don't create instances of Lister in threads
These are two fine remarks. but - how would you call (1) non-static method in run, without (2) creating
Lister object - the [static] Lister::walk() works from within run(), because I do not use non-statci method, I do not create Lister there, so I do not create no Qwidget out of GUI-widget.
3. Indeed I can left as it is - with 2 first methods in threads and others - out of there.
4. About nessecity to create qwidgets just in Main-gui (despite I do not read about it exactly in official Qt documentation) I did understand, as It seems to be 2 different widgets, so not composite one, despite Java suppoer so. As it is impossible in Qt it is very big deficiency, as I also could not assign value to Qlabel, or take the text from Qlinedit - in separate thread.
Administrator
Re: How to use separate threads for pushbuttons in QT (like SwingWorker in Java)
See the last two points.
Trivial to do with a signal from the thread connected to a slot in the label, line edit or any other class on the main thread.
Cheers,
_
Intermediate user
Re: How to use separate threads for pushbuttons in QT (like SwingWorker in Java)
"Trivial to do with a signal from the thread connected to a slot in the label" -- it is not so trivial for me.
I have looked for signals yesterday, and saw such sample
...Thread.h
signals: void signalmethod();
public: run();
then in thread.cpp
Thread::run() {
signalmethod();
} but I did it with static method. But here is non-static one?? what kind (how it should look like) of signal I shpuld use?
2. what 2 last point?
Administrator
Re: How to use separate threads for pushbuttons in QT (like SwingWorker in Java)
Right, just declare a signal and emit it in run.
The code creating the thread object can then connec this signal to its own slot or to the slot of another class.
E.g. if you had a signal like this
one could directly connect it to a label that should show that textQt Code:
Qt Code:
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