I am currently starting on QTCreator. I have been asked to use QTimers in a particular context which is this:
We have an open window,
One or more QTimers are triggered and make things appear on the screen every x msec.
When we press "Escape" the window should close and everything should be reset to 0.
But here is the problem, the timers are defined in a static way:
QTimer::singleShot(500, this, SLOT(foo());
When I call this->close() (which closes my window), the timers do not stop and continue. I tried several solutions: browse all the QTimers contained in my object, obviously there are none since they are defined in static. Instead of declaring them in static I've tried to create each time a new QTimer object like that:
QTimer *timer= new QTimer(this);
timer->setSingleShot(true);
timer->setInterval(2000);
timer->setParent(this);
timer->start();
And then call timer->stop() later, but I think it's very brutal when you have multiple Timers in the same code.
Is there a way to stop the timers when this->close is called, knowing that the timers are defined as a static one ?
Assuming you are using,
QWindow *qw = new QWindow();
QTimer *timer= new QTimer();
To solve the issue you need to connect destroyed() signal of QWindow to timer's slot stop()
So as soon as window is destroyed all registered timers will be stopped without explicit stop call. make sure you connect all timer instances. Code snippet as following,
QObject::connect(&qw, SIGNAL(destroyed()), timer, SLOT(stop()))
QObject::connect(&qw, SIGNAL(destroyed()), timer2, SLOT(stop()))
QObject::connect(&qw, SIGNAL(destroyed()), timer3, SLOT(stop()))
PS:
QTimer *timer= new QTimer(this); // here you are setting parent as 'this' already
timer->setSingleShot(true);
timer->setInterval(2000);
timer->setParent(this); // remove this, no need to set parent again.
timer->start();
Related
I'm trying to make a program in Qt. I will not send all, but the fragment with which I have a problem. The point is, I have to interrupt a function that has a Timer in it, but I don't know how to interrupt it while it's waiting before timer. 😕 Please reply!
void MainWindow::Test(){
TestWrite(); //TestWrite is a function where I write my answer
QTimer::singleShot(5000, this, &MainWindow::TestCheck); //TestCheck is a function where the answer is checked
}
void MainWindow::on_Test_clicked()
{
Test();
timer = new QTimer(this); //Creates a timer and calls the Test function every 7 seconds
timer->connect(timer, &QTimer::timeout, this, &MainWindow::Test);
timer->start(7000);
}
........
........
void MainWindow::on_Back_clicked()
{
timer->stop(); //I am trying to make the "Back" button interrupt the Test, TestWrite and TestCheck functions. Now, if you quickly click "Back" and "Test", the effect is as if you did not click the "Back" button
}
Timers in Qt that you start with the static QTimer functions (like you do in MainWindow::Test) cannot be stopped at all, because there's no timer object exposed to you that you could use to stop() (or otherwise manipulate) the timer. Such timers will expire in any case, and they will emit their signal in any case. You need to decide in your slot whether you're still interested in the signal.
When you create an explicit timer object (as you do in on_test_clicked(), you can only stop() it, or re-start() it with a minimum expiry time (0) to have it expire "immediately".
If you don't want to have a timer expire that you already started, simply stop() it.
The way you stated your question shows a possible mis-understanding of how timers work in Qt. Nothing is "waiting" for a timer, but rather an expired timer sends a signal to a slot. "Waiting" in Qt would freeze your user interface.
I have a quite lengthy foreach loop in a QDialog. It basically looks like this:
foreach (xxx, xxx) {
... doSomeStuff ...
QApplication::processEvents();
if (m_cancelMapLoading) {
break;
}
}
m_cancelMapLoading is set to true by clicking a "Cancel" button. The QApplication::processEvents(); makes this possible.
This works quite fine, but if the dialog is closed as long as that foreach loop still runs, it continues running. I tried to set m_cancelMapLoading to true in each function closing the dialog, but this does not help.
I also tried to test not only for m_cancelMapLoading being true, but also for isVisible(). This actually stops the dialog, but it re-opens it at once without the GUI elements in it.
Unfortunately, QtConcurrent::run etc. can't be used for the function, because the data structures that are manipulated by the foreach loop are not thread safe.
Is there a convenient way to solve this?
You can use a QTimer and Qt's parent-child structure to your advantage here. QTimer with a timeout value of zero has a special meaning in Qt
As a special case, a QTimer with a timeout of 0 will time out as soon
as all the events in the window system's event queue have been
processed. This can be used to do heavy work while providing a snappy
user interface:
So you could do something like
void Dialog::beginDoingStuff()
{
m_timer = new QTimer(this);
connect(m_timer, SIGNAL(timeout()), this, SLOT(processData());
m_timer->start(0);
}
void Dialog::processData()
{
// Perform one cycle of your process here
}
This will perform the processData() function in the same thread as the rest of the dialog, and when the dialog is destroyed by being closed, the timer will be deleted (because it's parent is the dialog), meaning the processing will stop.
A good and quite easy way to unload your GUI from heavy processing is assigning it to another thread or QtConcurrent.
You could then either poll a "should-I-terminate-yet?" variable or terminate the thread manually when it is no longer needed.
I highly recommend a parallel processing since offers better control rather than doing a "DoEvents"-like queue emptying.
We actually managed to solve the problem by connecting the dialog's finished signal to the click slot of the cancel button. This actually stops the loop in all circumstances.
We also introduced starting the function by a QTimer (for a nicer implementation not blocking the function where it's started), but this does not stop the loop (perhaps because we don't destroy the dialog when it's closed).
Thanks for all help :-)
I am writing a mathematical simulator in Qt5 and when I click a button, some heavy calculation needs to be done. During it, I want to display a Please, wait window, eventually with a progress bar. Preferably without using threads.
Problem is, during calculation the application hangs, events are not handled, and what should be a please, wait window is merely a window frame without any contents (looks transparent).
PC: AMD X2 L325, 2GB RAM, Radeon E4690
OS: Debian 6 (Squeeze, Old stable)
gcc 4.4.5, Qt 5.2.0
Any help would be appreciated!
While you could call QApplication::processEvents, it's not the best approach.
If you're avoiding threads because they're new to you, then I'm sure you'll find it much easier once you've done it once. Qt makes it easy.
All you need to do is create a class derived from QObject which will do the calculations. Next, create a thread and call the object's moveToThread function. The thread is then controlled with a few signals and slots. That's all there is to it.
Rather than repeat the content here, I suggest you read this article, which explains it in detail and provides clean and concise example code.
From the new object that processes your calculations, it can then emit a signal to a slot on the main thread, which will update the progress on your "Please Wait" window.
Note that Widgets and all rendering must be done on the main thread.
I prefer use Qt Concurrent. It is not well documented, but very handy, much better then using QThread directly.
I usually do such things like that I have separate QObject for logic, in there some slot which calls heavy calculation like that (see run documentation):
void MyCalculationClass::startCalculating() {
QtConcurent::run(this, &MyCalculationClass::doHeavyCalculation);
}
Where method doHeavyCalculation emits signals with progress and calculation results.
Usually this method operates on its own data not modified by other threads/methods, so if synchronization is needed, it is trivial. Signal-Slot mechanism is handling most of the multithreading issues (note that default connections detects that signals is emitted from other threads and queues slot calls in proper thread, it is done automatically by default).
i have such problem and i solve it like this, i make calculation in another thread( i use std::thread instad of QThread) before i start my calculation i just start timer
QTimer *timer = new QTimer(this);
connect(timer, SIGNAL(timeout()), this, SLOT(repaint()));
timer->start(1);
and then
std::thread t(&Widget::calcBackgound, this);
t.detach();
You can put the heavy and time consuming part of your code in run() member function of another class which inherits from QThread. After that create an instance of the new class and simply call its start() function.
Your new class can have a signal which emits the current progress value. you can then connect this signal to the slot of a progress bar.
Is it possible to call a function periodically in C++ with Qt function ?
And how to stop the timed function after it is set to be called periodically ?
If you are using qt, you can you QTimer which by default creates a repetitive timer.
There is an example in the documentation (shown below) and an example (Analog Clock).
QTimer *timer = new QTimer(this);
connect(timer, SIGNAL(timeout()), this, SLOT(update()));
timer->start(1000);
One possibility would be to use a QTimer timeout signal and a QObject slot. Connect the two and start() the timer.
http://qt-project.org/doc/qt-4.8/qtimer.html#timeout
To stop the timer, call stop().
As people have said in answers before me, you can use the timeout() signal to trigger a function to run.
If you want to stop the timer at some point, you can connect to the stop() slot, or call it directly yourself.
You can use the QTimer class.
Just declare a QTimer with the desired time interval, wrap your function in a QObject as a slot, and connect the QTimer's timeout() signal to the slot you just declared.
Then, when the condition for stopping calling the function is met, just call QTimer::stop().
Make a function that uses timer functionallity or a while loop that just waits for 100 ms and when your function meets the requirement just break. You could quite easy found a solution on this one if you just made a search among all the other questions that has been posted here.
I am trying to implement pause button for a game I am developing in Qt + OpenGL.
I want to implement it using QTimer.
Basically I am updating screen per 100ms. So in order to pause game, I will stop the timer on button press. and when button is again pressed i will start the timer again
Here is my pauseOrPlay SLOT:
void Window::pauseOrPlay()
{
GLWidget::modifyTimer = TRUE;
GLWidget::isPaused = !GLWidget::isPaused;
GLWidget timerUpdater;
timerUpdater.timerFunc();
}
and Here is my timerFunc()
GLvoid GLWidget::timerFunc()
{
static QTimer *timer = new QTimer(this);
connect(timer, SIGNAL(timeout()), this, SLOT(update()));
if( GLWidget::isPaused)
timer->start(100);
else
timer->stop();
}
But I am not getting the functionality. I get paused screen on this particular code and upon trying few tweaks here and there, sometimes I get screen updating very fastly which pointed me to this but I was unable to find cure to my problem somehow
Any help or Pointers?
PS: In this question there is nothing about OpenGL, but I think those are the people who might have dealt with similar think, adding OpenGL tag
That connection is in a bad place. You have it set up to connect each time you pause or resume the game. But if you connect multiple times, your slot will be called multiple tiles for each signal emission.
Make sure you only create the timer and connect to it once. I suggest moving the timer construction and signal connection into your GLWidget's constructor. Store a pointer to the timer as a member variable of your class so you can start and stop it in the class's member functions.