How to access object value inside the poll callback function ?

[Guttata]

Hi,

Thanks again for this awesome library.

I'm facing a conception issue using the poll function that i want to use to count encoder ticks on my robot.

Inside countTickPinA function, "this" does not refer to my Encoder object. How can i do to access its attributes (this.pinB, this.nbTicks) and methods (this.setTraveledDistance) ? Is it possible to pass other params to the callback function of poll ?

Thanks a lot

//Encoder class and constructor
function Encoder(name, pinA, pinB) {
    this.pinA = pinA
    this.pinB = pinB;
    this.nbTicks = 0;
    this.traveledDistance = 0; //distance in meter

    rpio.open(pinA, rpio.INPUT, rpio.PULL_DOWN);
    rpio.poll(pinA, this.countTickPinA);

    rpio.open(pinB, rpio.INPUT, rpio.PULL_DOWN);
    rpio.poll(pinB, this.countTickPinB);
}

//callback function of the rpio.poll
Encoder.prototype.countTickPinA = function (pinA){
    console.log("PIN A : ", pinA );
    console.log("PIN B : ", this.pinB);

    //Returns either 0 for LOW or 1 for HIGH
    var statePinA = rpio.read(pinA);
    var statePinB = rpio.read(this.pinB);

    // look for a low-to-high on channel A
    if (statePinA == 1){
        // check channel B to see which way encoder is turning
        if (statePinB == 0) {
            this.nbTicks = this.nbTicks - 1; //CW
        }
        else {
            this.nbTicks = this.nbTicks + 1; // CCW
        }
    }
    // must be a high-to-low edge on channel A
    else {
        // check channel B to see which way encoder is turning
        if (statePinB == 1) {
            this.nbTicks = this.nbTicks - 1; //CW
        }
        else {
            this.nbTicks = this.nbTicks + 1; //CCW
        }
    }
    console.log(this.nbTicks);
    this.setTraveledDistance();
}

[Guttata]

Hi,

I finally workaround like this : is it clean to do like this ?

function Encoder(name, pinA, pinB) {
    this.name = name;
    this.pinA = pinA
    this.pinB = pinB;
    this.nbTicks = 0;
    this.traveledDistance = 0; //distance in meter

    var encoder = this;

    rpio.open(pinA, rpio.INPUT, rpio.PULL_DOWN);
    rpio.poll(pinA, function countTickPinA(pinA){
        //Returns either 0 for LOW or 1 for HIGH
        var statePinA = rpio.read(pinA);
        var statePinB = rpio.read(encoder.pinB);

        // look for a low-to-high on channel A
        if (statePinA == 1){
            // check channel B to see which way encoder is turning
            if (statePinB == 0) {
                encoder.nbTicks = encoder.nbTicks - 1; //CW
            }
            else {
                encoder.nbTicks = encoder.nbTicks + 1; // CCW
            }
        }
        // must be a high-to-low edge on channel A
        else {
            // check channel B to see which way encoder is turning
            if (statePinB == 1) {
                encoder.nbTicks = encoder.nbTicks - 1; //CW
            }
            else {
                encoder.nbTicks = encoder.nbTicks + 1; //CCW
            }
        }
        console.log(name, " ", encoder.nbTicks);
        encoder.setTraveledDistance();
        } 
    );

    rpio.open(pinB, rpio.INPUT, rpio.PULL_DOWN);
    rpio.poll(pinB, function countTickPinB(pinB){
        //Returns either 0 for LOW or 1 for HIGH
        var statePinA = rpio.read(encoder.pinA);
        var statePinB = rpio.read(pinB);

        // look for a low-to-high on channel B
        if (statePinB == 1){
            // check channel A to see which way encoder is turning
            if (statePinA == 1) {
                encoder.nbTicks = encoder.nbTicks - 1; //CW
            }
            else {
                encoder.nbTicks = encoder.nbTicks + 1; //CCW
            }
        }
        // Look for a high-to-low on channel B
        else {
            // check channel B to see which way encoder is turning
            if (statePinA == 0) {
                encoder.nbTicks = encoder.nbTicks - 1; //CW
            }
            else {
                encoder.nbTicks = encoder.nbTicks + 1; //CCW
            }
        }
        console.log(name, " ", encoder.nbTicks);
        encoder.setTraveledDistance();
        } );
}

[AntonPieper]

Couldn't you have bound the function countTickPinA to this?

rpio.poll(pinA, this.countTickPinA.bind(this));