Centrals and Peripherals Are the Key Players in Core Bluetooth

In Bluetooth low energy communication, there are two key players: the central and the peripheral. Each player has a different role. A peripheral typically has data that is needed by other devices. A central typically uses the information served up by a peripheral to accomplish some task. For example, a digital thermostat equipped with Bluetooth low energy technology might provide the temperature of a room to an iOS app that then displays the temperature in a user-friendly way.

Each player performs a different set of tasks when carrying out its role. Peripherals make their presence known by advertising the data they have over the air. Centrals scan for nearby peripherals that might have data they’re interested in. When a central discovers such a peripheral, the central requests to connect to the peripheral and begins exploring and interacting with the peripheral’s data. The peripheral is responsible for responding to the central in appropriate ways.

Core Bluetooth Simplifies Common Bluetooth Tasks

The Core Bluetooth framework abstracts away the low-level details from the Bluetooth 4.0 specification. As a result, many of the common Bluetooth low energy tasks you need to implement in your app are simplified. If you are developing an app that implements the central role, Core Bluetooth makes it easy to discover and connect with a peripheral, and to explore and interact with the peripheral’s data. In addition, Core Bluetooth makes it easy to set up your local device to implement the peripheral role.

iOS App States Affect Bluetooth Behavior

When your iOS app is in the background or in a suspended state, its Bluetooth-related capabilities are affected. By default, your app is unable to perform Bluetooth low energy tasks while it is in the background or in a suspended state. That said, if your app needs to perform Bluetooth low energy tasks while in the background, you can declare it to support one or both of the Core Bluetooth background execution modes (there’s one for the central role, and one for the peripheral role). Even when you declare one or both of these background execution modes, certain Bluetooth tasks operate differently while your app is in the background. You want to take these differences into account when designing your app.

Even apps that support background processing may be terminated by the system at any time to free up memory for the current foreground app. As of iOS 7, Core Bluetooth supports saving state information for central and peripheral manager objects and restoring that state at app launch time. You can use this feature to support long-term actions involving Bluetooth devices.

Follow Best Practices to Enhance the User Experience

The Core Bluetooth framework gives your app control over many of the common Bluetooth low energy transactions. Follow best practices to harness this level of control in a responsible way and enhance the user’s experience.

For example, many of the tasks you perform when implementing the central or the peripheral role use your device’s onboard radio to transmit signals over the air. Because your device’s radio is shared with other forms of wireless communication, and because radio usage has an adverse effect on a device’s battery life, always design your app to minimize how much it uses the radio.