Pre-download remote content

When you distribute content remotely, you can improve performance by downloading dependencies in advance of when your application needs them. For example, you can download essential content on start up when your application is launched for the first time to make sure that users don't have to wait for content in the middle of gameplay.

Create a pre-download script

Use the Addressables.DownloadDependenciesAsync method to pre-download content so that it's cached on disk and faster to access when the application needs it. This method downloads an Addressable entity and any dependencies as a background task.


string key = "assetKey";

// Check the download size
AsyncOperationHandle<long> getDownloadSize = Addressables.GetDownloadSizeAsync(key);
yield return getDownloadSize;

//If the download size is greater than 0, download all the dependencies.
if (getDownloadSize.Result > 0)
{
    AsyncOperationHandle downloadDependencies = Addressables.DownloadDependenciesAsync(key);
    yield return downloadDependencies;
    if(downloadDependencies.Status == AsyncOperationStatus.Failed)
        Debug.LogError("Failed to download dependencies for " + key);

    // we need to release the download handle so the assets can be loaded
    downloadDependencies.Release();
}

Calling the Addressables.DownloadDependenciesAsync method loads the dependencies for the address or label that you pass in. Typically, this is the AssetBundle.

Tip

If you have a set of assets that you want to pre-download, you can assign the same label, such as preload, to the assets and use that label as the key when calling Addressables.DownloadDependenciesAsync. Addressables downloads all the AssetBundles containing an asset with that label if not already available, along with any AssetBundles containing the assets' dependencies.

Monitor download progress

An AsyncOperationHandle instance provides the following ways to get progress updates:

  • AsyncOperationHandle.PercentComplete: Reports the percentage of sub operations that have finished. For example, if an operation uses six sub operations to perform its task, the PercentComplete indicates the entire operation is 50% complete when three of those operations have finished (it doesn't matter how much data each operation loads).
  • AsyncOperationHandle.GetDownloadStatus: Returns a DownloadStatus struct that reports the percentage of total download size. For example, if an operation has six sub operations, but the first operation represented 50% of the total download size, then GetDownloadStatus indicates the operation is 50% complete when the first operation finishes.

The following example illustrates how you can use GetDownloadStatus to check the status and dispatch progress events during the download:


using System.Collections;
using UnityEngine;
using UnityEngine.AddressableAssets;
using UnityEngine.Events;
using UnityEngine.ResourceManagement.AsyncOperations;

internal class PreloadWithProgress : MonoBehaviour
{
    public string preloadLabel = "preload";
    public UnityEvent<float> ProgressEvent;
    public UnityEvent<bool> CompletionEvent;
    private AsyncOperationHandle downloadHandle;

    IEnumerator Start()
    {
        downloadHandle = Addressables.DownloadDependenciesAsync(preloadLabel, false);
        float progress = 0;

        while (downloadHandle.Status == AsyncOperationStatus.None)
        {
            float percentageComplete = downloadHandle.GetDownloadStatus().Percent;
            if (percentageComplete > progress * 1.1) // Report at most every 10% or so
            {
                progress = percentageComplete; // More accurate %
                ProgressEvent.Invoke(progress);
            }

            yield return null;
        }

        CompletionEvent.Invoke(downloadHandle.Status == AsyncOperationStatus.Succeeded);
        downloadHandle.Release(); //Release the operation handle
    }
}

To discover how much data you need to download to load one or more assets, you can call Addressables.GetDownloadSizeAsync:


AsyncOperationHandle<long> getDownloadSize =
    Addressables.GetDownloadSizeAsync(key);

The Result of the completed operation is the number of bytes that must be downloaded. If Addressables has already cached all the required AssetBundles, then Result is zero.

Always release the download operation handle after you have read the Result object. If you don't need to access the results of the download operation, you can automatically release the handle by setting the autoReleaseHandle parameter to true, as shown in the following example:


using System.Collections;
using UnityEngine;
using UnityEngine.AddressableAssets;

internal class Preload : MonoBehaviour
{
    public IEnumerator Start()
    {
        yield return Addressables.DownloadDependenciesAsync("preload", true);
    }
}
Note

On the WebGL platform, this API always returns the size of the AssetBundle, even if the AssetBundle has been cached. Cached AssetBundles aren't stored on the local file system, but persisted as part of the IndexedDB of the browser. WebGL Caching

Clear the dependency cache

If you want to clear any AssetBundles cached by Addressables, call Addressables.ClearDependencyCacheAsync. This method clears the cached AssetBundles containing the assets identified by a key along with any AssetBundles containing those assets' dependencies.

ClearDependencyCacheAsync only clears AssetBundles related to the specified key. If you updated the content catalog so the key no longer exists or it no longer depends on the same AssetBundles, then these AssetBundles remain in the cache until they expire based on cache settings.

To clear all AssetBundles, you can use the methods in the UnityEngine.Caching class.

If you want to ask the user for consent before download, use Addressables.GetDownloadSizeAsync to return how much space is needed to download the content from a given address or label. Note that this takes into account any previously downloaded AssetBundles that are still in Unity's AssetBundle cache.

When to download on demand

While it can be advantageous to download assets for your application in advance, there are instances where you might choose not to do so. For example:

  • If your application has a large amount of online content, and you expect users to only ever interact with some of it.
  • Your application must be connected online to function. If all your application's content is in small AssetBundles, you might choose to download content as needed.

Additional resources