What is wrong with QCompass?

Gourmet

I need device azimuth for my Android application.

In Qt docs there is very few info about QSensors programming. Finding some examples from here and there I made some code. First I initialize compass:

QCompass* compass;
.....
    compass = new QCompass(this);
    compass->setDataRate(5); // Hz
    connect( compass, SIGNAL(readingChanged()), this, SLOT(gotCompassData()) );
    qWarning()<<"********************** connecting to compass"<<compass->connectToBackend();

have got:

: (null):0 ((null)): ********************** connecting to compass true

Before I need azimuth call:

    compass->start();

And catch signal to slot:

void MyClass::gotCompassData()
{
    QCompassReading* reading = compass->reading();
    if( reading != Q_NULLPTR )
        qWarning()<<"device azimuth"<<reading->azimuth();
    else
        qWarning()<<"nothing read";
    compass->stop();
}

Data are requested periodically but in console I see only this:

(null):0 ((null)): device azimuth 0
(null):0 ((null)): device azimuth 0
(null):0 ((null)): device azimuth 0
(null):0 ((null)): device azimuth 0
(null):0 ((null)): device azimuth 0
(null):0 ((null)): device azimuth 0
(null):0 ((null)): device azimuth 0
(null):0 ((null)): device azimuth 0

in any device position.

I am pretty sure other compass simulating applications work fine on this device.
Result is the same with any

compass->setDataRate(5); // 100, 500, 0... doesn't matter

What I did wrong or what I did not?

jsulm

@gourmet said in What is wrong with QCompass?:

compass->stop();

Why do you stop the sensor in your slot?

Gourmet

@jsulm to not waste processor time when it is not neeed. It starts periodically from other thread.This does not affect the result - sensor sends "ready" data but they are zero. Why?

Gourmet

Wow! Things are more strange than I can imagine. Today I started work with this app - and suddenly have got proper azimuth values. Once. Next time when I run app - value become 0 again.

Gourmet

If I do not stop compass - it works. But it wastes resources cause it is not needed all the time. Once I stop compass when it is not needed - next app run it doesn't work. Looks like a bug.

Gourmet

Looks like I find workaround this. First I start compass in constructor of class using it. Then I stop compass little later. Next time I start it again when need azimuth and stop when get it. This way works - I get azimuth values in all program runs. But this is definitely a bug in QCompass.

Gourmet

Bug report.