How you load and manage assets in your project impacts on your application’s memory usage, load times, and build size. Unity provides several asset management systems, each designed for specific use cases and project sizes. Small applications with fixed content sizes can usually use Unity’s default asset management system. Systems like AssetBundles and Addressables provide better management for complex asset layouts, or applications that need to stream assets from remote servers.
By default, Unity uses the Scene List to determine which scenes and assets to include in a build and their load order. Unity only includes scenes in the SceneA Scene contains the environments and menus of your game. Think of each unique Scene file as a unique level. In each Scene, you place your environments, obstacles, and decorations, essentially designing and building your game in pieces. More info
See in Glossary List in a build, and unused scenes and assets not referenced from these scenes are excluded from a build. You can also use the SceneManager API to determine how to load scenes in your project.
The exception to this is if you include any scenes in a Resources folder, or mark them as Addressable, then Unity handles scenes differently.
To determine what content to build, Unity uses the following information:
Resources folder.Choosing the right approach depends on factors like your target platform, content delivery requirements, and whether you need dynamic loading capabilities. The following management systems are available:
Resources folders in your project with the Resources API.AssetBundle API. You can then store AssetBundles remotely and download on demand.AssetBundle API, it automates a lot of the manual processes that the AssetBundle system has, and provides a Unity Editor interface.
Direct reference asset management is the default way of managing assets at runtime in Unity. Whenever you drag an asset into a scene or onto a component through the InspectorA Unity window that displays information about the currently selected GameObject, asset or project settings, allowing you to inspect and edit the values. More info
See in Glossary window of the Unity Editor, you create a direct reference to that asset. When you build your application, Unity saves any referenced assets in a separate file associated with the scenes in your project.
You can use direct references with ScriptableObject instances to efficiently manage large asset sets and reduce build sizes. A benefit of only using direct references is that Unity only includes assets that your project directly references in the build, so your application doesn’t load unnecessary or duplicated assets.
Direct references have some limitations, as follows:
For more information, refer to Direct reference asset management.
The Resources system provides a simple way of managing assets in memory. To use the Resources system, you create a folder called Resources in your project and add assets to it. During the build process, Unity finds the assets in the Resources folder and bundles them into a serialized file with metadata and indexing information. You can then use the Resources API to load and unload the assets in your application.
The Resources system has the following limitations:
Resources folders are always included in the Player build, even if they’re not referenced by anything. This can lead to large build sizes.Resources.Load remain in memory until explicitly unloaded with Resources.UnloadUnusedAssets, which unloads all unused assets loaded by Resources, or until the scene that used them is unloaded.Resources folder, then building and starting your application can take a long time.Resources.Load returns null and becomes a runtime error, so you need to manually track which assets are needed.It’s an ideal system for prototyping, or for smaller projects which need assets throughout the lifetime of the application. For more information, refer to Use AssetBundles to load assets at runtime.
Use the AssetBundle system to organize assets into separate container files called AssetBundles. You can store AssetBundle files in your project files, or remotely in the cloud.
The AssetBundle API minimizes the impact on network and system resources by allowing you to download AssetBundles on demand. You can use this on-demand behavior to add DLC and post-release content updates to your application. For example, you can deliver new content for your game without requiring users to download a new version of your game. The AssetBundle API then provides a way to load and unload assets from downloaded bundles.
The AssetBundle system has the following limitations:
AssetBundle API doesn’t keep track of asset dependencies. For example, if you want to load a prefabAn asset type that allows you to store a GameObject complete with components and properties. The prefab acts as a template from which you can create new object instances in the scene. More infoAssetBundle API isn’t aware of whether an AssetBundle is hosted locally or remotely, so you need to keep track of the location of all the AssetBundles in your project.For more information, refer to Introduction to AssetBundles.
The Addressables package provides a user interface in the Unity Editor to manage and organize the assets in your project. It’s built on top of the AssetBundle API and automatically manages dependencies, asset locations, and memory allocation, which you otherwise have to handle manually in the AssetBundle system. The Addressables package aims to remove the limitations of the Resources and AssetBundle system to make it easier to manage assets on demand.
Once you have made an asset Addressable, you can reference it by address in your code, rather than by its file name or AssetBundle location, which means you can change the location of an asset without needing to rewrite any code. You can also use asset references to dynamically load and unload assets, so that you don’t have to keep all assets in the scene in memory at all times.
The Addressables system is designed for applications that have assets stored on a CDN, and those that are likely to have content updates over time. If your application has fixed content which is shipped in the initial download, then using direct references, or the Resources system is a better alternative to Addressables or AssetBundles.
For more information, refer to Addressables overview
The Entities package has its own content management system, where you use weak references to assets to load them at runtime. You can also create content archives to deliver content to an application. For more information, refer to Introduction to content management.