外设自身改变特征值时如何实现更新值回调

Question

Suppose if the peripheral is listening to some socket or pipe in which I am sending a value which will modify the characteristic. How can I notify that change to the central device? Both peripheral and central devices are running on the Linux platform. Because whatever the Pizza example given for Linux device will notify the central only when central is writing something. Suppose if the value is changed by some program outside Bleno an noble where I should implement the updateValueCallback() ? Is it on onSubscribe or onNotify ?

Answer 1

You should use the onSubscribe() event.

onSubscribe() fires when the central (GATT Server) subscribes to notifications from your peripheral, whereas onNotify() fires when a notification is sent, after the central has subscribed.

For example, I've defined my characteristic as follows:

var customCharacteristic = function() {
    bleno.Characteristic.call(this, {
        uuid: 'UUID_HERE',
        properties: ['read', 'notify', '... etc'],
        //Subscribe event
        onSubscribe = function(maxSize, updateValueCallback){
            console.log('subscribe'); //output that we've subscribed
            //Now the central has subscribed, poll something 
            //(the sensor or whatever you're using) every half 
            //second to see if the value has updated
            setInterval(function() {
                //poll sensor or get value or something
                updateValueCallback(new Buffer([VALUE]);
            }, 500);
        },
        //Notify event
        onNotify = function(){
            console.log('notify'); //to show when notification is being sent
        }
    });
}

//Don't forget to deal with when the central unsubscribes, you might want to stop the interval ticker!

Roughly based on this article, with some ideas from here .