Android: How do bluetooth UUIDs work?
I don't understand what a bluetooth UUID denotes. Do UUIDs denote protocols (eg RFCOMM)? If so, why do the createRfcommSocketToServiceRecord() methods require UUIDs, when they specify rfcomm right in their names? Why does the BluetoothChat sample code have a seemingly arbitrary, hardcoded UUID?
My question arises because, as per this question, I'm getting a null pointer exception when devices running 4.0.4 try to connect (to an external, non-android device) using reflection. However, the solution to that question doesn't work for me. UUID muuid = device.getUuids()[0].getUuid(); raises an exception.
Edit : I've solved that problem by hardcoding the UUID for Serial port service as per this answer (using UUID.fromString("00001101-0000-1000-8000-00805f9b34fb"); ).
I'm further puzzled by why I need to supply a UUID to create an unsecured rfcomm socket using createInsecureRfcommSocketToServiceRecord(), but not using the reflection method.
Can anyone straighten me out?
It usually represents some common service (protocol) that bluetooth device supports.
When creating your own rfcomm server (with listenUsingRfcommWithServiceRecord ), you should specify your own UUID so that the clients connecting to it could identify it; it is one of the reasons why createRfcommSocketToServiceRecord requires an UUID parameter.
Otherwise, some common services have the same UUID, just find one you need and use it.
See here
The UUID is used for uniquely identifying information. It identifies a particular service provided by a Bluetooth device. The standard defines a basic BASE_UUID: 00000000-0000-1000-8000-00805F9B34FB .
Devices such as healthcare sensors can provide a service, substituting the first eight digits with a predefined code. For example, a device that offers an RFCOMM connection uses the short code: 0x0003
So, an Android phone can connect to a device and then use the Service Discovery Protocol (SDP) to find out what services it provides (UUID).
In many cases, you don't need to use these fixed UUIDs. In the case your are creating a chat application, for example, one Android phone interacts with another Android phone that uses the same application and hence the same UUID.
So, you can set an arbitrary UUID for your application using, for example, one of the many random UUID generators on the web (for example).
UUID is similar in notion to port numbers in Internet. However, the difference between Bluetooth and the Internet is that, in Bluetooth, port numbers are assigned dynamically by the SDP (service discovery protocol) server during runtime where each UUID is given a port number. Other devices will ask the SDP server, who is registered under a reserved port number, about the available services on the device and it will reply with different services distinguishable from each other by being registered under different UUIDs.
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