EntityManager

EntityManager is the subsystem in the Scene responsible to manage Entities. It is responsible to maintain the Entity list, and the lifecycle of each one.

Useful ways to interact with EntityManager:

Add and Remove Entities

The most common way to interact with EntityManager is by adding and removing entities:

EntityManager entityManager = scene.Managers.EntityManager;

// Add an Entity to the Scene..
entityManager.Add(entity);

// Remove an Entity from the Scene...
entityManager.Remove(entity);

Important Properties

Method	Description
EntityGraph	Return the entities at the top level on the scene (Those without parent)
AllEntities	Return all the entities of the scene, including those who have parent.

Find Entities

You can find Entities in several ways:

Find Entity by EntityPath

This is the most common way to find an Entity in the Scene, by using its EntityPath:

// Find an entity by its Entity Path...
var entity = entityManager.Find("Parent.Entity1.ChildEntity");

Find Entity by ID

You can find an Entity if you specify its ID (Guid)

// Find an entity by its ID...
Guid id = entity.Id;
var entity = entityManager.Find(id);

Find all Entities by Tag

As we mentined before, you can set the tag Entities by setting the Tag property. So, you can obtain an Entity collection that match a given Tag:

// Find all entities with a given Tag...
IEnumerable<Entity> entityCollection = entityManager.FindAllByTag("Tag");

Entity Tag Collection

A useful feature of EntityManager is the possibility to obtain a live collection of entities that match a specified Tag.

This collection is represented by the EntityTagCollection class. The main advantage compared to invoke FindAllByTag() method is that in this case the collection is dynamic during the application lifetime. So, you can subscribe to events to get notified when the collection changes:

Here it is a glimpse of how to use it:

// Gets the tag collection...
var tagCollection = entityManager.GetEntityTagCollection("Tag");

// Iterates over all matching entities...
foreach (var entity in tagCollection.Entities)
{
    System.Console.WriteLine(entity.EntityPath);
}

// TagCollection Events:

// OnEntityAdded: Event triggered when a new Entity with the given Tag is added to the Scene...
tagCollection.OnEntityAdded += (sender, entity) => 
{ 
    System.Console.WriteLine($"New entity: {entity.EntityPath}"); 
};

// OnEntityRemoved: Event triggered when an Entity is no longer belong to this collection, 
// becuase the Entity is removed or its Tag has changed...
tagCollection.OnEntityRemoved += (sender, entity) =>
{
    System.Console.WriteLine($"Entity removed: {entity.EntityPath}");
};