How to Break an Infinite Loop using QPushButton? - qt

Question

I have an infinite loop, inside the loop I want to insert a state whenever I click a button, it will break the current loop.
I've tried several ways like:
if(ui->btnStop->isDown())
{
break;
}
if(ui->btnStop->isChecked())
{
break;
}
and
if(cv::waitKey(10)>=0)
{
break;
}
But, it doesn't work.
I wonder why cv::waitKey doesn't work in Qt, but in a non-Qt project it will work flawlessly.
Are there any other way to break an infinite loop with a QPushButton?
Any help would be appreciated.

Answer 1

It doesn't work because the event processor cannot run whilst execution is locked in your loop. The easiest solution is to simply call QApplication::processEvents() in each loop, this will force the event processor to run.
// Add a boolean to your class, and a slot to set it.
MyClass
{
...
private slots:
void killLoop() { killLoopFlag_ = true; }
private:
bool killLoopFlag_;
}
// In the constructor, connect the button to the slot.
connect( ui->btnStop, SIGNAL( clicked() ),
this, SLOT( killLoop ) );
// Then when performing the loop, force events to be processed and then
// check the flag state.
killLoopFlag_ = false;
while ( true ) {
// ...Do some stuff.
QApplication::processEvents();
if ( killLoopFlag_ ) {
break;
}
}
However you need to ask yourself: Should I be doing long running calculations inside the GUI thread? The answer is usually no.