Need 2 widgets without a parent to comunicate

[boblatino]

If the signals are cross-thread then they will be queued rather than the slot executing synchronously. Making the connections at line 37-41 Qt::QueuedConnection as they would be in the threaded scenario does not affect the performance. Perhaps you could produce a small example that more closely matches what you are doing.

Hi ChrisW67, Im using a plain connect so it should be detected and working as a queued connect as shows in the documentation. The next I will do is force a Qt::QueuedConnection instead of relaing in Qt::AutoConnection. On monday I will have a pc with visual studio and I will create an example. Its basicaly the same as the above message, but instead of a QTimer that emits the signals, is a plain OS thread. The thread just dequeues elements and calls emit. Does you see an issue to have 2 widgets parentless that interact? Is this the correct way to doit?


Thanks
Ramiro

[wysota]

Could you prepare a minimal compilable example reproducing the problem?

[boblatino]

Could you prepare a minimal compilable example reproducing the problem?

Yes, on monday I will post a compilable example. I now dont have visual studio in my laptop.

Thanks
Ramiro

[wysota]

I now dont have visual studio in my laptop.

You can use MinGW, we won't mind

[boblatino]

You can use MinGW, we won't mind

Here is an example:

class window : public QWidget
{
	Q_OBJECT
 
public:
	window(QWidget *parent = 0, Qt::WFlags flags = 0) : QWidget(parent, flags)
	{
 
	}
 
public slots:
	void showMe()
	{
		show();
	}
 
	void hideMe()
	{
		hide();
	}
 
};
 
class consumerThread : public QThread
{
	Q_OBJECT	
 
	public:
		consumerThread(fifo<int> & f):f(f)
		{
			start();
		}
 
		void run()
		{
			while(true)
			{
				int a;
				f.pop(a);
				if(a == 0)
				{
					emit showMe1();
					emit hideMe1();
				}
				else
				{
					emit showMe2();
					emit hideMe2();
				}
			}
		}
 
	signals:	
		void showMe1();
		void showMe2();
		void hideMe1();
		void hideMe2();
	private:
 
		fifo<int> & f;
 
};
 
class producerThread : public QThread
{
	public:
		producerThread(fifo<int> & f):f(f)
		{
			start();
		}
 
		void run()
		{
			while(true)
			{
				f.push(0);
				Sleep(1000);
				f.push(1);
				Sleep(1000);
			}
		}
	private:
 
		fifo<int> & f;
 
};
 
class dispatcher : public QObject
{
	Q_OBJECT
 
public:
	dispatcher()
	{
		consumerThread* consumer = new consumerThread(queue);
		producerThread* producer = new producerThread(queue);
		window1 = new window();
		window2 = new window();
 
		connect(consumer, SIGNAL(showMe1()), window1, SLOT(showMe()));
		connect(consumer, SIGNAL(showMe2()), window2, SLOT(showMe()));
		connect(consumer, SIGNAL(hideMe1()), window1, SLOT(hideMe()));
		connect(consumer, SIGNAL(hideMe2()), window2, SLOT(hideMe()));
	}
private:
	fifo<int> queue;
	window* window1;
	window* window2;
 
};

class window : public QWidget
{
	Q_OBJECT

public:
	window(QWidget *parent = 0, Qt::WFlags flags = 0) : QWidget(parent, flags)
	{
	
	}

public slots:
	void showMe()
	{
		show();
	}

	void hideMe()
	{
		hide();
	}

};

class consumerThread : public QThread
{
	Q_OBJECT	
	
	public:
		consumerThread(fifo<int> & f):f(f)
		{
			start();
		}
		
		void run()
		{
			while(true)
			{
				int a;
				f.pop(a);
				if(a == 0)
				{
					emit showMe1();
					emit hideMe1();
				}
				else
				{
					emit showMe2();
					emit hideMe2();
				}
			}
		}

	signals:	
		void showMe1();
		void showMe2();
		void hideMe1();
		void hideMe2();
	private:

		fifo<int> & f;

};

class producerThread : public QThread
{
	public:
		producerThread(fifo<int> & f):f(f)
		{
			start();
		}
		
		void run()
		{
			while(true)
			{
				f.push(0);
				Sleep(1000);
				f.push(1);
				Sleep(1000);
			}
		}
	private:

		fifo<int> & f;

};

class dispatcher : public QObject
{
	Q_OBJECT

public:
	dispatcher()
	{
		consumerThread* consumer = new consumerThread(queue);
		producerThread* producer = new producerThread(queue);
		window1 = new window();
		window2 = new window();

		connect(consumer, SIGNAL(showMe1()), window1, SLOT(showMe()));
		connect(consumer, SIGNAL(showMe2()), window2, SLOT(showMe()));
		connect(consumer, SIGNAL(hideMe1()), window1, SLOT(hideMe()));
		connect(consumer, SIGNAL(hideMe2()), window2, SLOT(hideMe()));
	}
private:
	fifo<int> queue;
	window* window1;
	window* window2;

};

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Thanks
Ramiro

[wysota]

Starting a thread in its constructor is in general a bad idea. But back to the main issue... you are aware that slots of a QThread subclass are executed in the context of the main thread and not the thread controlled by the QThread object, right? Please also explain what is the point in emitting showMe1() and immediately after that emitting hideMe1().

It could be simpler to explain what effect you want to achieve and we will suggest a better approach.

[boblatino]

you are aware that slots of a QThread subclass are executed in the context of the main thread and not the thread controlled by the QThread object, right?

No, I didnt know that, but in the real code the thread is a OS thread (via CreateThread).

Please also explain what is the point in emitting showMe1() and immediately after that emitting hideMe1()

It has no point sorry. It should be

emit showMe1();
emit hideMe2();

emit showMe1();
emit hideMe2();

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The idea is an application that has more than 1 top level window and a dispatcher that controls which window is shown. Sometimes it could be no window shown and sometimes 2 at the same time. The issue that we are facing now is that when a widget is hidden and other is put in the front (show), the first time you touch the window (we are using touchscreen), the event is processed by the hidden widget. The second time, the shown widget captures the event normaly. I have called activateWindow also but with no luck. Is there a better approach on this? I dont want to create and close (destroy) the widgets all the time so I have created them once and show / hide accordly. If I create them and destroy every time I dont have this problem.

Thanks
Ramiro

[wysota]

I don't think we can help you if you show us code that does something different than the one you are actually using...

If the two windows are never shown together maybe you should use a QStackedWidget instead of two widgets?

Anyway... if I wanted to have a mechanism for switching windows, I'd do it more or less like this:

class Dispatcher : public QObject {
  Q_OBJECT
public:
  void addWindow(QWidget *win) {
    m_windows << win;
    if(m_current == -1) {
      setWindow(0);
    }
  }
public slots:
  void next() {
    setWindow(m_current+1 % m_windows.count());
  }
  void prev() {
    setWindow(m_current-1 % m_windows.count());
  }
  void setWindow(int which) {
    if(m_current == which) return;
    if(m_current!=-1) {
      m_windows.at(m_current)->hide();
    }
      m_current = which;
      m_windows.at(m_current)->show();
    qApp->processEvents(); // optionally force event processing (don't unless sure it's required)
  }
private:
  QList<QWidget *> m_windows;
  int current = -1;
};

class Dispatcher : public QObject {
  Q_OBJECT
public:
  void addWindow(QWidget *win) {
    m_windows << win;
    if(m_current == -1) {
      setWindow(0);
    }
  }
public slots:
  void next() {
    setWindow(m_current+1 % m_windows.count());
  }
  void prev() {
    setWindow(m_current-1 % m_windows.count());
  }
  void setWindow(int which) {
    if(m_current == which) return;
    if(m_current!=-1) {
      m_windows.at(m_current)->hide();
    }
      m_current = which;
      m_windows.at(m_current)->show();
    qApp->processEvents(); // optionally force event processing (don't unless sure it's required)
  }
private:
  QList<QWidget *> m_windows;
  int current = -1;
};

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Then it's just a matter of connecting a signal to one of the slots defined in the dispatcher.

[boblatino]

Thanks wysota, so that will be another way of show / hide the windows, but why the inactive window (hidden) takes the focus instead of the one that is shown the first time? After just a click the shown window it will regain focus and work. I have also called activateWindow but it doesnt take the control of the focus. Also I dont understand why a hidden window can take the user event of a press.


Thanks
Ramiro

[GreenScape]

when you have QueuedConnection emit post event. that event must be processed by event loop in concrete widget; because only one parentless widet wokrs with main event loop at same time(the signal is posted but nobody cares, because main event loop processing another widget's events) you should create event loops for both threads.

OR

you should inherit from QDialog and use exec(); instead show(); because exec creates own dialog's event loop.

[boblatino]

when you have QueuedConnection emit post event. that event must be processed by event loop in concrete widget; because only one parentless widet wokrs with main event loop at same time(the signal is posted but nobody cares, because main event loop processing another widget's events) you should create event loops for both threads.

So I must create 2 separate threads one per window? That will cause synchronization issues. Is possible to create multiple loops without a new thread?

Thanks
Ramiro

[GreenScape]

no, u just should to create event loop for each widget.

example:

create 2 threads, inside each thread create widget, and event loop.
this will look like 2 applications, each widget in its own thread, but in fact it will be one app