What the custom UUID mean for BLE in IOS Sample?

Question

I am new to iOS development, and study about Bluetooth Low Energy (BLE, Bluetooth 4.0) for IOS.

I studied the sample code of this link BTLE Central Peripheral Transfer.

And there is another similar sample in this link iOS 7 SDK: Core Bluetooth - Practical Lesson

The applications on the above two links talk about send and receive the text data between two IOS device base on BLE. The App can select to be a central or Peripheral , and the central will receive the text data send from the Peripheral.

It define the UUID like the following code in header file.

#define TRANSFER_CHARACTERISTIC_UUID    @"08590F7E-DB05-467E-8757-72F6FAEB13D4"

And after the Central connect to the Peripheral , it discover the characteristic from Peripheral.

If the UUID is equal to TRANSFER_CHARACTERISTIC_UUID ,then subscribe it by using setNotifyValue:YES like the following code.

- (void)peripheral:(CBPeripheral *)peripheral didDiscoverCharacteristicsForService:(CBService *)service error:(NSError *)error
{
    // Again, we loop through the array, just in case.
    for (CBCharacteristic *characteristic in service.characteristics) {

        // And check if it's the right one
        if ([characteristic.UUID isEqual:[CBUUID UUIDWithString:TRANSFER_CHARACTERISTIC_UUID]]) {

            // If it is, subscribe to it
            [peripheral setNotifyValue:YES forCharacteristic:characteristic];
        }
    }

    // Once this is complete, we just need to wait for the data to come in.
}

The question is like the following:

First Question:

I can not find this UUID:@"08590F7E-DB05-467E-8757-72F6FAEB13D4" in Bluetooth Development Portal. Is that create by uuidgen in terminal ?

The second Question:

If I am Central ,and I have subscribe the characteristic by using setNotifyValue:YES like the above code.

The BLE will tell the Central there has new data send from Peripheral by following code , is the concept correct ?

- (void)peripheral:(CBPeripheral *)peripheral didUpdateValueForCharacteristic:(CBCharacteristic *)characteristic error:(NSError *)error

I am new in IOS development and BLE.

Thanks in advance.

Answer 1

First question:

• Yes, Apple even suggests generating those UUIDs using uuidgen in the various WWDC video. The 128-bit UUIDs are not standardized by the Bluetooth SIG and you can use those to run your own profiles.

Second question:

• Yes, you first discover the services, then the characteristics, then setNotifyValue:YES. From now on, you will receive notifications from the peripheral via [-CBPeripheralDelegate didUpdateValueForCharacteristic:error:]. The same callback will be invoked when you read a characteristic manually (there's no way to distinguish the read response from a notification in Core Bluetooth).