---
uid: input-system-step-4-device-registration
---

# Step 4 Device registration and creation

You now have a functioning device, but you haven't registered it (added it to the system) yet. This means you can't see the device when, for example, you create bindings in the [Action editor](actions-editor.md).

You can register your device type with the system from within the code that runs automatically as part of Unity's startup. To do so, modify the definition of `MyDevice` like so:

```CSharp
// Add the InitializeOnLoad attribute to automatically run the static
// constructor of the class after each C# domain load.
#if UNITY_EDITOR
[InitializeOnLoad]
#endif
public class MyDevice : InputDevice, IInputUpdateCallbackReceiver
{
    //...

    static MyDevice()
    {
        // RegisterLayout() adds a "Control layout" to the system.
        // These can be layouts for individual Controls (like sticks)
        // or layouts for entire Devices (which are themselves
        // Controls) like in our case.
        InputSystem.RegisterLayout<MyDevice>();
    }

    // You still need a way to trigger execution of the static constructor
    // in the Player. To do this, you can add the RuntimeInitializeOnLoadMethod
    // to an empty method.
    [RuntimeInitializeOnLoadMethod(RuntimeInitializeLoadType.BeforeSceneLoad)]
    private static void InitializeInPlayer() {}
}
```

This registers the Device type with the system and makes it available in the Control picker. However, you still need a way to add an instance of the Device when it is connected.

In theory, you could call [`InputSystem.AddDevice<MyDevice>()`](xref:UnityEngine.InputSystem.InputSystem) somewhere, but in a real-world setup you likely have to correlate the Input Devices you create with their identities in the third-party API.

It might be tempting to do something like this:

```CSharp
public class MyDevice : InputDevice, IInputUpdateCallbackReceiver
{
    //...

    // This does NOT work correctly.
    public ThirdPartyAPI.DeviceId externalId { get; set; }
}
```

and then set that on the Device after calling [`AddDevice<MyDevice>`](xref:UnityEngine.InputSystem.InputSystem). However, this doesn't work as expected in the Editor, because the Input System requires Devices to be created solely from their [`InputDeviceDescription`](xref:UnityEngine.InputSystem.Layouts.InputDeviceDescription) in combination with the chosen layout (and layout variant). In addition, the system supports a fixed set of mutable per-device properties such as device usages (that is, [`InputSystem.SetDeviceUsage()`](xref:UnityEngine.InputSystem.InputSystem) and related methods). This allows the system to easily recreate Devices after domain reloads in the Editor, as well as to create replicas of remote Devices when connecting to a Player. To comply with this requirement, you must cast that information provided by the third-party API into an [`InputDeviceDescription`](xref:UnityEngine.InputSystem.Layouts.InputDeviceDescription) and then use an [`InputDeviceMatcher`](xref:UnityEngine.InputSystem.Layouts.InputDeviceMatcher) to match the description to our custom `MyDevice` layout.

This example assumes that the third-party API has two callbacks, like this:

```CSharp
public static ThirdPartyAPI
{
    // This example assumes that the argument is a string that
    // contains the name of the Device, and that no two Devices
    // have the same name in the external API.
    public static Action<string> deviceAdded;
    public static Action<string> deviceRemoved;
}
```

You can hook into those callbacks and create and destroy devices in response.

```CSharp
// This example uses a MonoBehaviour with [ExecuteInEditMode]
// on it to run the setup code. You can do this many other ways.
[ExecuteInEditMode]
public class MyDeviceSupport : MonoBehaviour
{
    protected void OnEnable()
    {
        ThirdPartyAPI.deviceAdded += OnDeviceAdded;
        ThirdPartyAPI.deviceRemoved += OnDeviceRemoved;
    }

    protected void OnDisable()
    {
        ThirdPartyAPI.deviceAdded -= OnDeviceAdded;
        ThirdPartyAPI.deviceRemoved -= OnDeviceRemoved;
    }

    private void OnDeviceAdded(string name)
    {
        // Feed a description of the Device into the system. In response, the
        // system matches it to the layouts it has and creates a Device.
        InputSystem.AddDevice(
            new InputDeviceDescription
            {
                interfaceName = "ThirdPartyAPI",
                product = name
            });
    }

    private void OnDeviceRemoved(string name)
    {
        var device = InputSystem.devices.FirstOrDefault(
            x => x.description == new InputDeviceDescription
            {
                interfaceName = "ThirdPartyAPI",
                product = name,
            });

        if (device != null)
            InputSystem.RemoveDevice(device);
    }

    // Move the registration of MyDevice from the
    // static constructor to here, and change the
    // registration to also supply a matcher.
    protected void Awake()
    {
        // Add a match that catches any Input Device that reports its
        // interface as "ThirdPartyAPI".
        InputSystem.RegisterLayout<MyDevice>(
            matches: new InputDeviceMatcher()
                .WithInterface("ThirdPartyAPI"));
    }
}
```