> ## Documentation Index
> Fetch the complete documentation index at: https://docs.appcharge.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Implement the Callbacks

To implement the Auto Update SDK, include the following callback methods:

| Method                    | Description                                                                                                                                                                                                                                       |
| ------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `OnInitializationSuccess` | Triggered when SDK initialization is successful.                                                                                                                                                                                                  |
| `OnUpdateStatus`          | Triggered when a new version of the app is available, and immediately after invoking the `checkForUpdate()` method.                                                                                                                               |
| `OnDownloadStarted`       | Triggered when permission to install has been granted by the player, and the download process begins. The SDK will attempt to download the new app version.                                                                                       |
| `OnProgress`              | Triggered when the download is initiated and when every new byte or packet is downloaded thereafter. You may use it to show download progression in real-time.                                                                                    |
| `OnDownloadEnded`         | Triggered when the download process is complete.                                                                                                                                                                                                  |
| `OnInstallationReady`     | Triggered when the SDK is ready to start the installation process.                                                                                                                                                                                |
| `OnError`                 | Triggered when an error occurs during the update process, including initialization failures. Follow the instructions in the [Unity Auto Update SDK troubleshooting](./troubleshooting) article and try to re-initialize again based on the error. |

## Example code

Below is the example code for the implementation:

```csharp theme={"system"}
using Appcharge.Updater;
using Appcharge.Updater.Interfaces;
using Appcharge.Updater.Models;
using UnityEngine;
using UnityEngine.UI;

public class Sample : MonoBehaviour, IUpdateCallback
{
    [SerializeField] private Text _logger;
    [SerializeField] private Button _btnCheckForUpdate;
    [SerializeField] private Button _btnInstallUpdate;

    private UpdateStatusModel _status;

    private void Start()
    {
        UpdateController.Instance.Init("sandbox", "checkoutPublicKey", "customerId", this);
    }

    #region Interface Callback Methods

    public void OnInitializationSuccess()
    {
        _logger.text = "Initialization successful.";
        _btnCheckForUpdate.gameObject.SetActive(true);
    }

    public void OnUpdateStatus(UpdateStatusModel status)
    {
        _status = status;
        _logger.text = $"A new version of your app is available: {status.Message}";
        _btnInstallUpdate.gameObject.SetActive(true);
    }

    public void OnDownloadStarted()
    {
        _logger.text = "Downloading the new app version.";
    }

    public void OnProgress(int progress)
    {
        _logger.text = $"Progress: {progress}%";
    }

    public void OnDownloadEnded()
    {
        _logger.text = "The new app version has been downloaded.";
    }

    public void OnInstallationReady()
    {
        _logger.text = "The new app version has been downloaded and is ready to install.";
    }

    public void OnError(int errorCode)
    {
        _logger.text = $"Error: {errorCode}";
    }

    #endregion

    public void CheckForUpdates()
    {
        UpdateController.Instance.CheckForUpdates();
    }

    public void InstallUpdate()
    {
        if (_status == null)
        {
            _logger.text = "No status";
            return;
        }

        if (_status.IsUpdateAvailable)
        {
            UpdateController.Instance.InstallUpdate();
        }
    }
}
```