# MDLComponent The base protocol for extensible file format support in Model I/O. ``` protocol MDLComponent : NSObjectProtocol ``` ## Overview By extending this protocol in your own custom protocols, you can define new functionality to add to the [`MDLObject`](/documentation/ModelIO/MDLObject) instances in the object graph corresponding to a [`MDLAsset`](/documentation/ModelIO/MDLAsset) instance. Model I/O adopts this pattern to support container objects (with the [`MDLObjectContainerComponent`](/documentation/ModelIO/MDLObjectContainerComponent) protocol) and objects with associated transformations (with the [`MDLTransformComponent`](/documentation/ModelIO/MDLTransformComponent) protocol). To work with these aspects of a Model I/O object, call the object’s [`componentConforming(to:)`](/documentation/ModelIO/MDLObject/componentConforming(to:)) method with the appropriate protocol. (The [`MDLObject`](/documentation/ModelIO/MDLObject) class also provides convenience methods and properties for accessing features of these components without directly accessing the component instances.) To add your own object features, first define a protocol that extends the [`MDLComponent`](/documentation/ModelIO/MDLComponent) protocol, implement a class that adopts that protocol, and then use the [`setComponent(_:for:)`](/documentation/ModelIO/MDLObject/setComponent(_:for:)) method to add your component to each object that needs it. The example below shows how you might implement a file format that associates scripting event triggers with parts of a game scene. ```objc @protocol MyScriptTriggerComponent // key: trigger identifier, value: scripting-language code @property NSDictionary *scriptTriggers; @end @interface MyScriptTriggerStorage @property NSDictionary *scriptTriggers; @end @implementation MDLObject (MyScriptTriggers) - (void)setScriptTriggers:(NSDictionary)triggers { MyScriptTriggerStorage *storage = [self componentConformingToProtocol:@protocol(MyScriptTriggerComponent)]; if (storage == nil) { storage = // ... allocate / manage storage ... [self setComponent:storage forProtocol:@protocol(MyScriptTriggerComponent)]; } storage.scriptTriggers = triggers; } @end ``` ## Relationships ### Conforming Types [`MDLObjectContainer`](/documentation/ModelIO/MDLObjectContainer) [`MDLTransformStack`](/documentation/ModelIO/MDLTransformStack) [`MDLAnimationBindComponent`](/documentation/ModelIO/MDLAnimationBindComponent) [`MDLTransform`](/documentation/ModelIO/MDLTransform) ### Inherits From [`NSObjectProtocol`](/documentation/ObjectiveC/NSObjectProtocol) ### Inherited By [`MDLObjectContainerComponent`](/documentation/ModelIO/MDLObjectContainerComponent) [`MDLTransformComponent`](/documentation/ModelIO/MDLTransformComponent) --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)