How to get data from an object returned from a Bluetooth device using BLE

Ah okay, thank you I no longer get the error nut still get no output. Am I supposed to set _onCharRead to something in the onCharacteristicRead function as my code never enters the following if statement:

if ((null != onCharRead) && onCharRead.stillAlive()) {
(onCharRead.get() as DeviceManager).procCharWrite(value);
System.println("read");

}

Is that perhaps something you need to do in one of the notify functions?

Have you tried putting a System.println() call right in your onCharacterisicRead() function?  Do the same in your onCharacteristicChanged function, just to make sure which is getting called.

The problem was I never initialized onCharRead my function now passes the value ByteArray to the following function in Device Manger:

public function procCharWrite(value as ByteArray) as Void {
var pd = value.decodeNumber(Lang.NUMBER_FORMAT_UINT16, {});
System.println(pd);

}

But I still get the same error for decodeNumber despite it being a ByteArray that it is altering now:

Error: Symbol Not Found Error
Details: Could not find symbol 'decodeNumber'
Stack:
- procCharWrite() at C:\Users\PC-User\eclipse-workspace\PowerMeterBLE\source\DeviceManager.mc:102 0x100005ee
- onCharacteristicRead() at C:\Users\PC-User\eclipse-workspace\PowerMeterBLE\source\PowerMeterBLEDelegate.mc:69 0x100002de

Actually, I think the problem is that value still isn't a ByteArray somehow as when I run the function like this:

It only prints "got to proCharWrite" and not "it's a ByteArray"

I do pass it in as a ByteArray in onCharacteristicRead:

So I have no clue what type the "value" variable could be in proCharWrite

Value is the 3rd parameter passed to onCharacteristicRead().  It is a byre array.  right before the var onCharRead-_onCharRead;

do

System.println(value);

and you should see what you are getting back from the read, 

Ah that seems to have solved it thank you, I now get an empty list for _powerMeterData but I have tried it with a different service and it works fine. I'll have to figure out whether the UUID is wrong or the power meter just isn't outputting anything as it's not being pushed properly. Thanks for the help much appreciated.

Apologies for all the questions but when you implement onCharacteristicChanged can you make it similar to onCharacteristicRead such that the notify looks like:

public function notifyCharChanged(manager as DeviceManager) as Void {
System.println("CharChanged");
_onCharChanged = manager.weak();
}

and the function looks like:

public function onCharacteristicChanged(characteristic as BluetoothLowEnergy.Characteristic,value as Lang.ByteArray) as Void {

var onCharChanged = _onCharChanged;
if ((null != onCharChanged) && onCharChanged.stillAlive()) {
(onCharChanged.get() as DeviceManager).procCharWrite(value);
System.println("read");
}
}

Or do you have to implement a queue of some sort 

Again, the bye array is passed to onCharactisticChanged as "vaule".  It just like onCharacteristicRead, but no status is passed.

As far as a queue, you'll likely need on for issuing thee read requests or ti turn on notify.

So if you want to reead 3 xharacteristic, do the first one, then in onCharacteristicReadm the second one, then again in onCharacteristicRead again, the third one.

I hopefully will just need to read from one Characteristic if it gives me general power meter data. So in theory, if the value in the characteristic changes it will notify onCharacteristic by calling notifyCharChanged just as it does on onCharacteristicRead? Its just that I have put some print statements in the onCharChanged functions and they never print, but that could of course indicate that the value never changes

You need to send a message to enable notify on the devices I've used.  The NordicThingy52 Sample has some queuing to just send those requests.