Vive La Vida Bluetooth

We now have a complete, operational SDK and application.

Here is Our Ending Repo Tag.

This application demonstrates Bluetooth on all the current Apple platforms, from one codebase: Mac OS X, iPhone/iPod, iPad, Watch, and TV.

This codebase is compiled into four targets; native Swift-based frameworks that are focused on one (or more) of the above platforms. Currently, the functionality is as barely simple as possible. It just scratches the surface of Core Bluetooth, but does demonstrate a complete system, from a Peripheral, advertising Services, to a Central, scanning for Services, and connecting to Peripherals, in order to use those Services to communicate with the Peripheral.

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At this point, the Peripheral is getting the question. Time to answer it.

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In this entry, we’ll do a detailed code walkthrough of the changes that were made to get to this point.

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We are now ready to have the Central Mode ask a question to one of its Magic 8-Balls.

After we are done with this step, we will be able to run an instance of the app as a Central (on a Mac, iPhone/iPad/iPod, Watch or TV), and an instance of the app as a Peripheral (on a Mac or iPhone/iPad/iPod).

The Central will discover the Peripheral, and display its name in the list. The user will then be able to select the Peripheral, and “ask it a question.”

The Peripheral device will almost immediately display the question.

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In this entry, we will walk through the code that we needed to add to the SDK/Central Mode to discover and register devices.

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THIS IS NOT STRAIGHTFORWARD –NOT EVEN A LITTLE

One thing that we’ll learn about Core Bluetooth (which can also apply to other types of asynchronous communication), is that nothing is really direct or straightforward.

That means that we can’t just ask a CBCentralManager instance for its CBPeripherals. We need to ask the manager to discover the Peripherals, and, possibly, build up its own list; which we can then query.

The same goes for Services. We can’t just ask a CBPeripheral object for its CBService instances. We have to ask it to discover its Services.

After that, each Service needs to discover its Characteristics. That said, just to add insult to injury, we don’t ask the Service to discover its Characteristics; we ask the Peripheral to do so, on behalf of the Service.

Once the Characteristics have been discovered, then we can finally aggregate the Peripheral device.

We did just enough on the Peripheral side to give the Central something to find.

The Central, however, has its work cut out for it…

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Now that we have the Central and Peripheral devices finding each other, we need to start “filling in the blanks.”

That begins in the Peripheral, where we will create an instance of the Core Bluetooth Service, and populate it with the two Characteristics we chose.

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We are now ready to start actually implementing the Bluetooth code.

Apple’s Core Bluetooth SDK uses the concept of “Managers” to implement Bluetooth capabilities for Central and Peripheral devices.

If we will be running the device as a Bluetooth Central, then we will instantiate CBCentralManager. If we will be running as a Peripheral, then we instantiate CBPeripheralManager. An instance of one these will be associated with each of the SDK instances that we create, and we will be managing these “under the radar.” The user of the SDK will not have any idea these are being used.

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In order to actually instantiate Core Bluetooth managers, we need to make sure that our apps are ready for it.

There’s an important info.plist key that needs to be set, and, for the Mac, we also need to check a box.

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An important part of setting up a Bluetooth system, is registering unique GATT IDs for our Service and Characteristics.

“GATT” is an acronym for “Generic ATTribute profile.” It is defined here. There are a number of “predetermined” types of services, and we can add to them.

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