GATT Service

Peripheral Manager (GATT Server)

This allows you to accept client connections

Each OS has different limitations and functions

On iOS - you need to advertise as well as create a gatt server

Services

Services are nothing more than categories in the overall perspective of BluetoothLE. You should be aware that you must setup all characters & descriptors that belong to a service BEFORE starting advertising or adding a service to a running server!

You should always know your service UUID for future client consumption!

From a functionality perspective, there is not a lot you do with services

General Setup

After creating your server instance and a service, you can do the following:

You should always assign a known GUID ID to your characteristic in order for your GATT service to be consumed by a client.

Below are examples of a basic read/write characteristic and a notification characteristic setup

var service = CrossBleAdapter.Current.AddService(new Guid(...));

var characteristic = service.AddCharacteristic(
    Guid.NewGuid(),
    CharacteristicProperties.Read | CharacteristicProperties.Write | CharacteristicProperties.WriteWithoutResponse,
    GattPermissions.Read | GattPermissions.Write
);

var notifyCharacteristic = service.AddCharacteristic
(
    Guid.NewGuid(),
    CharacteristicProperties.Indicate | CharacteristicProperties.Notify,
    GattPermissions.Read | GattPermissions.Write
);

Characteristics

These are the heart and soul of BLE. This is where data is exchanged between client & server

Read

When you have a read characteristic, you need to hook on to its read observable

characteristic.WhenReadReceived().Subscribe(x =>
{
    var write = "HELLO";

    // you must set a reply value
    x.Value = Encoding.UTF8.GetBytes(write);

    x.Status = GattStatus.Success; // you can optionally set a status, but it defaults to Success
});

Write

Same with write characteristic

characteristic.WhenWriteReceived().Subscribe(x =>
{
    var write = Encoding.UTF8.GetString(x.Value, 0, x.Value.Length);
    // do something with value

    // note that you can reply with a value and status here as well (like a read)
});

Notification Subscriptions

It is important to know how many subscribers you have to know if you should be processing notifications

Subscribers are nothing more than device UUIDs for identification. From an IOS perspective, there is almost zero you can do with them

notifyCharacteristic.WhenDeviceSubscriptionChanged().Subscribe(e =>
{
    var @event = e.IsSubscribed ? "Subscribed" : "Unsubcribed";
}

// you can also see a current list of subscribers

notifyCharacteristic.SubscribedDevices

Sending Notifications

Now that you have some subscribers, lets say hello every second just for fun

// or you can pass to a select list of subscribers
await notifyCharacteristic.Notify(bytes, notifyCharacteristic.SubscribedDevices.First());

// you can also listen to the callbacks for each broadcast
await notifyCharacteristic.Notify(bytes);