Registering an EventHandler in a class

[komodo108]

Below is an example of the problem, the MicroBit should print "Hi" whenever an action occurs, but is printing nothing.

#include "MicroBit.h"

class test {
    private:
        MicroBit* uBit;
    public:
        test(MicroBit* microbit) {
            uBit = microbit;
            uBit->serial.send("hiii");
            uBit->messageBus.listen(MICROBIT_ID_GESTURE, MICROBIT_EVT_ANY, this, &test::event);
        }

        void event(MicroBitEvent e) {
            uBit->serial.send("Hi");
        }
};

MicroBit uBit;

int main() {
    uBit.init();
    test thetest(&uBit);
    while(true) {}
    release_fiber();
}

I am following the example method from here. Also, adding in more debugging to this, such as adding a print to serial from just above the messageBus.listen() call works.

[pelikhan]

Remove while(true) {}.

[komodo108]

Sadly, that did not work. Same behaviour as before.

[finneyj]

Really? Did you keep the release_fiber() in there? That call deletes the main thread and releases any associated resources back to the system.

Removing the while(true) loop should be the way to go, or do a uBit.sleep() operation in there while loop (or anything else that blocks). We're running a non-preemtpive scheduler to help keep things simpler for the kids...

[finneyj]

OK - I can reproduce this. Something afoot. Looking into it...

[komodo108]

@finneyj Sorry for the mistake! I was just following the tutorial from here, I removed changed the loop to: while(true) { uBit.sleep(10000); } and have tried both with and without the call to release_fiber() and there is still no change when moving the MicroBit.

Just saw the second comment, and thank you :)

[finneyj]

Something funky in the MessageBus event handling in this case I think, and/or the lazy instantiation of the gesture recognizer. If you try this (which is really just the same as your code with an addition C style handler, both event handlers trigger for me.)

#include "MicroBit.h"

class test {
    private:
        MicroBit* uBit;
    public:
        test(MicroBit* microbit) {
            uBit = microbit;
            uBit->messageBus.listen(MICROBIT_ID_GESTURE, MICROBIT_EVT_ANY, this, &test::event);
        }

        void event(MicroBitEvent e) {
            uBit->serial.printf("EVT2\n");
        }
};

MicroBit uBit;
test thetest(&uBit);

void allGestures(MicroBitEvent e) {
    uBit.serial.printf("EVT1\n");
}

int main() {
    uBit.init();
    uBit.messageBus.listen(MICROBIT_ID_GESTURE, MICROBIT_EVT_ANY, allGestures);

    while(1)
    {
        uBit.serial.send("Hi\n");
        uBit.sleep(2000);
    }
    release_fiber();
}

[finneyj]

Ahh, OK. I get it. :)

You had test thetest(&uBit); as a local variable in main. This means your class instance would be declared on the stack of the main thread. This could then get paged out, and the instance of your class is therefore not always in memory where you think it is. generally a good idea not to declare anything on the stack of a thread that is accessed outside the given function/method... if that makes sense?

This slight variant on your code works for me:

[finneyj]

#include "MicroBit.h"

class test {
    private:
        MicroBit* uBit;
    public:
        test(MicroBit* microbit) {
            uBit = microbit;
            uBit->messageBus.listen(MICROBIT_ID_GESTURE, MICROBIT_EVT_ANY, this, &test::event);
        }

        void event(MicroBitEvent e) {
            uBit->serial.send("Hi");
        }
};

MicroBit uBit;

int main() {
    uBit.init();
    new test(&uBit);
    release_fiber();
}

[komodo108]

Thanks so much!