Fix: Unity Addressables Download Progress Callback Not Firing

Here is how to fix Unity Addressables download progress that never updates between 0 and 100. Your loading screen freezes at 0%, then jumps directly to complete. Or you call handle.PercentComplete and get values that bear no resemblance to actual bytes downloaded. The Addressables API exposes two different progress sources, and only one of them is what you actually want for a download UI.

The Symptom

You start a content download with Addressables.DownloadDependenciesAsync(label). Your UI subscribes to handle.Completed hoping for incremental progress, but only gets a single callback at the end. You try handle.PercentComplete and observe values like 0, 0, 0, 1 with nothing between. Players see a stuck progress bar even though the network is clearly active.

What Causes This

Completed is a one-shot event. AsyncOperationHandle exposes a Completed callback, not a progress callback. It fires exactly once when the entire operation finishes. There is no built-in per-frame event for progress.

PercentComplete averages internal stages. The PercentComplete property tracks the operation through several phases (initialization, dependency resolution, download, load). For a content-only download, the value can spike from 0 to 1 because most stages are instant.

Asset is already cached. If the bundle is already on disk, no download happens and the progress is meaningless. Always check GetDownloadSizeAsync first to determine if a download is even necessary.

autoReleaseHandle dropping the handle early. If you call DownloadDependenciesAsync with autoReleaseHandle: true and store the handle, the handle becomes invalid as soon as the operation completes. Polling it for progress after that throws or returns nonsense.

The Fix

Step 1: Use GetDownloadStatus and poll. Spin a coroutine that updates the UI every frame.

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

public class ContentDownloader : MonoBehaviour
{
    [SerializeField] private string downloadLabel = "dlc_pack_1";
    [SerializeField] private UnityEngine.UI.Slider progressBar;

    public IEnumerator DownloadAndTrack()
    {
        AsyncOperationHandle sizeHandle = Addressables.GetDownloadSizeAsync(downloadLabel);
        yield return sizeHandle;

        long totalBytes = (long)sizeHandle.Result;
        if (totalBytes == 0) yield break;  // Cached, nothing to download

        AsyncOperationHandle handle = Addressables.DownloadDependenciesAsync(
            downloadLabel, autoReleaseHandle: false);

        while (!handle.IsDone)
        {
            DownloadStatus status = handle.GetDownloadStatus();
            progressBar.value = status.Percent;
            yield return null;
        }

        Addressables.Release(handle);
    }
}

Step 2: Use bytes for accurate UI text. Showing “42 MB / 120 MB” reads more clearly than “35%”.

DownloadStatus s = handle.GetDownloadStatus();
label.text = $"{s.DownloadedBytes / 1048576}MB / {s.TotalBytes / 1048576}MB";

Step 3: Disable autoReleaseHandle when polling. If you want to read the handle after completion, pass autoReleaseHandle: false and release manually.

Step 4: Handle errors gracefully. Network drops are common on mobile. Watch for handle.Status == AsyncOperationStatus.Failed and surface a retry option.

if (handle.Status == AsyncOperationStatus.Failed)
{
    Debug.LogError($"Download failed: {handle.OperationException}");
    Addressables.Release(handle);
    ShowRetryButton();
}

Why GetDownloadStatus and Not PercentComplete

GetDownloadStatus walks the dependency tree and sums up only the download bytes for assets that are actually being fetched. PercentComplete divides total operations into stages with implementation-defined weights. The two values can disagree by 30% or more during a real download. For a player-facing UI, always use GetDownloadStatus.

“Poll the handle. Use bytes. Release manually. Network failures need a retry path.”

Related Issues

For other Addressables download problems, see Addressables Failed To Load and Remote Catalog Update Failing.

PercentComplete lies. GetDownloadStatus does not.