Interacting with entity components

This page details the ways that a Unity worker can find out about and interact with the components on SpatialOS entities.

The code used to do this is generated from schema when you run spatial worker codegen. When you change your schema, you need to run codegen to get the up-to-date code to use.

For information about creating components, see the schema documentation.

On this page:

• Prerequisites
• Get the value of a property
• Set the value of a property
• Responding to a change of a property
• Triggering an event
• Responding to an event
• Sending a command
• Responding to a command request

Prerequisites

MonoBehaviours must be added to the prefab associated with the entity. The methods will be run on the current entity/GameObject. To do things to another entity/GameObject, you can either run a query, or expose the methods using Unity and the GameObject.

The Unity SDK changes the usual MonoBehaviour lifecycle of Unity. Component readers and writers will be available when the OnEnable event function is called. For more information have a look at MonoBehaviour lifecycle.

All the examples on this page use a component reader (an IComponentReader) or writer (an IComponentWriter), imported like this:

[Require]
private Improbable.ExampleComponent.Reader exampleComponentReader;

[Require]
private Improbable.ExampleComponent.Writer exampleComponentWriter;

The Reader and Writer interfaces are nested inside the classes of their corresponding components.

Get the value of a property

Prerequisites:

• the MonoBehaviour needs a component reader or writer for the relevant component
• the worker must have read access on the component

To get the current value of a property, use exampleComponentReader.Data.ExampleProperty. exampleComponentReader.Data contains the full persistent properties of the component.

Set the value of a property

Prerequisites:

• the MonoBehaviour needs a component writer for the relevant component
• the worker must have write access on the component

To set the value of a property, use exampleComponentWriter.Send(), which takes an Update object.

To create an update object that changes a property:

// Create the update object
var update = new ExampleComponent.Update();

// Add a property change to the update object
update.SetExampleProperty(1);

// Send the update to SpatialOS
exampleComponentWriter.Send(update);

You can update multiple properties in the same update, like this:

// Create the update object
var update = new ExampleComponent.Update();

// Add the property changes to the update object
update.SetExampleProperty(1);
update.SetAnotherExampleProperty(2);

// Send the update to SpatialOS
exampleComponentWriter.Send(update);

You can send an update in one line like this:

exampleComponentWriter.Send(new ExampleComponent.Update().SetExampleProperty(1));

Note that:

• Anything set in the Update will be sent to SpatialOS, even if the value hasn’t changed, and empty updates won’t be dropped.
• Don’t try to modify an Update object once it’s sent. If you want to modify it later and perhaps re-use it, send a copy of it instead, for example by doing exampleComponentWriter.Send(update.DeepCopy()).
• If you change a property’s value multiple times, for example by doing update.SetExampleProperty(1).SetExampleProperty(2);, only the last value will be sent.
• The update will be observed (the update applied to .Data and callbacks invoked) by the worker once it’s processed, typically on the next frame.

Note: You can trigger events in the same way, and mix property and event changes in one update. See below.

Responding to a change of a property

Prerequisites:

• the MonoBehaviour needs a component reader or writer for the relevant component
• the worker must have read access on the component

Register callbacks on change of a specific property, or for any property change on the component, using exampleComponentReader.ExamplePropertyUpdated, or exampleComponentReader.ComponentUpdated respectively.

Register all callbacks in OnEnable or later, and deregister them in OnDisable, in order to prevent unexpected and hard-to-debug errors.

These callbacks:

• Are invoked whenever an update to the property is received. The property won’t necessarily have changed.
• Do not get called immediately on registration. If you want to invoke the callback when it’s registered, use exampleComponentReader.ComponentUpdated.AddAndInvoke instead.

Example:

private void OnEnable()
{
    // Register callbacks for component and property change
    exampleComponentReader.ComponentUpdated.Add(OnExampleComponentUpdated);
    exampleComponentReader.ExamplePropertyUpdated.Add(OnExamplePropertyUpdated);
}

private void OnDisable()
{
    // Deregister callbacks
    exampleComponentReader.ComponentUpdated.Remove(OnExampleComponentUpdated);
    exampleComponentReader.ExamplePropertyUpdated.Remove(OnExamplePropertyUpdated);
}

private void OnExampleComponentUpdated(Component.Update update)
{
    // Respond to the component change here
}

void OnExamplePropertyUpdated(int examplePropertyValue)
{
    // Respond to the property change here
}

Triggering an event

Prerequisites:

• the MonoBehaviour needs a component writer for the relevant component
• the worker must have write access on the component

To trigger an event, use exampleComponentWriter.Send(), which takes an Update object.

To create an update object that triggers an event:

// Create the update object
var update = new Improbable.ExampleComponent.Update();

// Create an instance of the event, and give it data
var exampleEvent = new Improbable.ExampleComponent.ExampleEvent();
exampleEvent.eventValue = 2;

// Add the event to the update object
update.AddExampleEvent(exampleEvent);

// Send the update to SpatialOS
exampleComponentWriter.Send(update);

Note that:

• Anything set in the Update will be sent to SpatialOS, even if the value hasn’t changed, and empty updates won’t be dropped.
• Don’t try to modify an Update object once it’s sent. If you want to modify it later and perhaps re-use it, send a copy of it instead, for example by doing exampleComponentWriter.Send(update.DeepCopy()).
• The update will be observed (the update applied to .Data and callbacks invoked) by the worker once it’s processed, typically on the next frame.

Note: You can set properties in the same way, and mix property and event changes in one update. See above.

Responding to an event

Prerequisites:

• the MonoBehaviour needs a component reader or writer for the relevant component
• the worker must have read access on the component

Register callbacks for events using exampleComponentReader.ExampleEventTriggered.

Register all callbacks in OnEnable() or later, and deregister them in OnDisable, in order to prevent unexpected and hard-to-debug errors.

private void OnEnable()
{
    // Register callback for the event
    exampleComponentReader.ExampleEventTriggered.Add(OnExampleEvent);
}

private void OnDisable()
{
    // Deregister callback
    exampleComponentReader.ExampleEventTriggered.Remove(OnExampleEvent);
}

private void OnExampleEvent()
{
    // Respond to the event here
}

Sending a command

You define commands in the schema, and the definition includes an input type and a return type.

When you send a command, register a callback to receive a response, which includes:

• information about the command’s success or failure
• a response object of the return type

It is guaranteed that SpatialOS will only report a command’s success if it actually succeeded, but no other guarantees are made.

Prerequisites:

• the MonoBehaviour needs a component writer - this doesn’t need to be on the component the command is on (it’s just used to avoid commands being sent repeatedly)
• the worker must have write access on the component

To send a command, use Send{name of command} on the SpatialOS utility class (using Improbable.Unity.Core):

SpatialOS.Commands.SendExampleCommand(...).OnSuccess(successCallback).OnFailure(failureCallback);

• SendCommand() returns an ICommandResponseHandler object which exposes the following methods:

  • OnSuccess(CommandSuccessCallback<TResponse> successCallback) is the callback triggered if the command succeeds.
  • OnFailure(CommandFailureCallback failureCallback) is the callback triggered if the StatusCode != StatusCode.Success.
    

  You don’t have to specify either of these callbacks if you don’t want to. * TResponse Response is the response object, of the type defined in the schema.

• writer is the component writer used to avoid commands being sent repeatedly.

• commandDescriptor is a special object identifying a command. Command descriptors are generated for each command defined in your schema, and are named as {ComponentName}.Commands.{CommandName}.Descriptor. To access the available list of commands you can invoke on a component, try typing “{ComponentName}.Commands.” and looking at your code completion results. (This will only work once you’ve run spatial worker codegen).

• request is the request argument to the command, of the type specified in the schema. Here, that’s DamageRequest.

• entityId is the ID of the entity you are sending the command to.

For example:

void RunACommand(EntityId exampleEntityId) 
{
  SpatialOS.Commands
    .SendCommand(someComponentWriter, ExampleComponent.Commands.ExampleCommand.Descriptor, new ExampleCommandRequest(), exampleEntityId)
    .OnSuccess(OnExampleCommandRequestSuccess)
    .OnFailure(OnExampleCommandRequestFailure);
}

void OnExampleCommandRequestSuccess(ExampleResponse response)
{
    Debug.Log("Command succeeded.");
}

void OnExampleCommandRequestFailure(ICommandErrorDetails response)
{
    Debug.LogError("Failed to send command, with error: " + response.ErrorMessage);
}

For a full example, see the command recipe.

Responding to a command request

To decide which worker should respond to a command, look at which workers have access to the component containing the command. Whichever worker has write access to the component will be sent the command request, and should respond. For example, if the UnityWorker has write access to a player’s Health component, the UnityWorker should implement the command.

You can respond to a command:

• synchronously, using exampleComponentWriter.CommandReceiver.OnTakeDamage.RegisterResponse
• asynchronously, using

Respond to a command by registering a callback using exampleComponentWriter.CommandReceiver.OnExampleCommand. The callback is passed a ResponseHandle object which has:

• the incoming request (.Request) member
• a method to send back the response (.Respond(CommandReturnType response))
• information data about the command caller - its WorkerId and attributes (.CallerDetails)

Register all callbacks in OnEnable() or later, and deregister them in OnDisable, in order to prevent unexpected and hard-to-debug errors.

For example:

public void OnEnable() 
{
    // Register callback for the command being received
    exampleComponentWriter.CommandReceiver.OnExampleCommand.RegisterResponse(RespondToExampleCommand);
}
public void OnDisable()
{
    // Deregister callback
    exampleComponentWriter.CommandReceiver.OnExampleCommand.DeregisterResponse();
}

private void ExampleResponse RespondToExampleCommand(ExampleRequest request, ICommandCallerInfo callerInfo)
{
    // Do what is requested in the command here

    // Send a response to the requester of the command
    return new ExampleResponse();
}

For a full example, see the command recipe page.

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