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Unity Engine

AssetBundle caching

Use Unity's built-in caching system to prevent redundant downloads.
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Unity's built-in disk-based caching system prevents redundant downloads by storing AssetBundles downloaded via 
UnityWebRequestAssetBundle
.
Unity converts AssetBundles in the cache to LZ4 for optimal performance. If 
Caching.compressionEnabled
 is 
false
, AssetBundles are stored uncompressed. Use the 
Caching
 class to manage cached AssetBundles, for example to clear or check cache presence.
If you use the Web platform, refer to Web caching for more information on how to handle caching.
If you use 
UnityWebRequestAssetBundle.GetAssetBundle
, only those that accept a 
Hash128
or 
uint version
argument use the built-in cache.
When downloading without caching, Unity downloads the AssetBundle into a memory file then loads it. If the downloaded file is in LZMA format then Unity recompresses it into a memory file in LZ4 format and loads that instead.

Location of the AssetBundle cache

The local AssetBundle cache exists at a root folder (for example, 
Application.temporaryCachePath
), with a structure like the following:
RootCacheFolder- BundleName1   - Hash1 __data (AssetBundle content)   - Hash1__info (cache metadata)- BundleName2  - Hash2 __data   - Hash2 __info
During download, Unity uses a temporary directory for the incoming data, and then establishes the recompressed AssetBundle in this structure.
By default, the last component of the download URL is used as the AssetBundle name for the cache. To change the name, you can specify it in the 
CachedAssetBundle.name
structure, which can be passed to some 
UnityWebRequestAssetBundle.GetAssetBundle
signatures. Note that the cache is based on the AssetBundle name, not the full URL.

Cache version hash

The AssetBundle cache uses hash values as the version of an AssetBundle. You can provide a 128-bit hash (
Hash128
) or 32-bit 
uint
value to distinguish versions. This can be a build-generated hash, a numeric version, or a custom value. It's crucial to update this version when a new AssetBundle build is released so devices download the correct new version rather than using a stale cached one.
重要
Unity doesn't automatically perform hash calculations on AssetBundles during download and load to verify content against a provided version hash. The version hash is only an identifier. Cyclic redundancy checks (CRC) are available for content validation.
You can also use 
BuildAssetBundleOptions.ForceRebuildAssetBundle
 to perform a full rebuild, and 
BuildAssetBundleOptions.AssetBundleStripUnityVersion
 to prevent changes to the hash between Unity versions.

Cache clearing

Unity performs cache clearing automatically on desktop systems. It checks the cache on startup, and clears any AssetBundles that haven't been accessed in 
Cache.expirationDelay
 in the last 150 days.
The platform providers for mobile devices maintain their caches. To explicitly clear the cache on mobile platforms use 
Cache.ClearCache
.

Additional resources