Arma Reforger:Resource Usage

A Resource object is a source of data through many classes (BaseResourceObject and its BaseContainer, IEntitySource etc). Due to how resource references are managed, some safeties are required.

Good Practice

Resources are managed by the engine, outside of script's reach. If the script loses reference to a Resource object, the engine may dispose of it instantly or at some point in the future, deleting also its related BaseContainer/IEntitySource/etc objects (it is impossible to have a strong ref to a BaseContainer object in script).
To avoid this, always keep a reference to the parent Resource.

Examples

Bad Example	Good Example
static BaseContainer GetBaseContainer(ResourceName resourceName) { // the only reference to said Resource is here and will be lost at the end of the scope Resource resource = Resource.Load(resourceName); if (!resource.IsValid()) return null; return resource.GetResource().ToBaseContainer(); // resource's reference is dropped here // the returned BaseContainer may become null at any time, // even with a script's reference }	static BaseContainer GetBaseContainer(notnull Resource resource) { if (!resource.IsValid()) return null; return resource.GetResource().ToBaseContainer(); // resource's reference is managed by the method caller }
// GetBaseContainer being the above method BaseContainer baseContainer = GetBaseContainer(m_sPrefab); string name = baseContainer.GetClassName(); // may result in a null pointer exception	Resource resource = Resource.Load(m_sPrefab); BaseContainer baseContainer = GetBaseContainer(resource); string name = baseContainer.GetClassName(); // fine as long as a reference to resource is kept
// beware of loops! array<BaseContainer> baseContainers = {}; // strong ref is not possible Resource resource; foreach (ResourceName resourceName : resourceNames) { resource = Resource.Load(resourceName); if (!resource.IsValid()) continue; baseContainers.Insert(resource.GetResource().ToBaseContainer()); // reference to resource is lost at each loop end } Process(baseContainers); // the array may contain nulls	array<ref Resource> resources = {}; array<BaseContainer> baseContainers = {}; Resource resource; foreach (ResourceName resourceName : resourceNames) { resource = Resource.Load(resourceName); if (!resource.IsValid()) continue; resources.Insert(resource); baseContainers.Insert(resource.GetResource().ToBaseContainer()); // reference to resource is kept in the resources array } Process(baseContainers); // all references are kept resources = null; // this can now be done without issue
N/A	// this is fine - a Managed instance is created, resource reference can be dropped // simplified, from SCR_BaseContainerTools.CreateInstanceFromPrefab() static Managed CreateInstanceFromPrefab(ResourceName prefab) { Resource resource = Resource.Load(prefab); if (!resource.IsValid()) return null; BaseContainer baseContainer = resource.GetResource().ToBaseContainer(); if (!baseContainer) return null; return BaseContainerTools.CreateInstanceFromContainer(baseContainer); // resource reference is dropped but the created instance will remain }