unity2022 下载文件,支持断点续传，支持GUI进度显示

在Unity 2022中实现文件下载并支持断点续传，同时支持GUI进度显示可以使用UnityWebRequest来实现。以下是一个简单的示例：

public class DownloadManager : MonoBehaviour
{
    private UnityWebRequest request;
    private string savePath;
    private long fileSize;
    private long bytesDownloaded;
    private bool isDownloading;

    // GUI进度条相关
    private float progress;
    private Rect progressRect = new Rect(50, 50, 200, 20);

    public void Download(string url, string savePath)
    {
        if (isDownloading)
            return;

        this.savePath = savePath;

        request = UnityWebRequest.Head(url);
        request.SendWebRequest();
        StartCoroutine(GetFileSize());
    }

    IEnumerator GetFileSize()
    {
        while (!request.isDone)
            yield return null;

        if (request.result != UnityWebRequest.Result.Success)
        {
            Debug.LogError("获取文件大小失败！");
            yield break;
        }

        fileSize = long.Parse(request.GetResponseHeader("Content-Length"));

        if (File.Exists(savePath))
        {
            FileInfo fileInfo = new FileInfo(savePath);
            bytesDownloaded = fileInfo.Length;
            request = UnityWebRequest.Get(request.uri.ToString());
            request.SetRequestHeader("Range", "bytes=" + bytesDownloaded + "-");
        }
        else
        {
            request = UnityWebRequest.Get(request.uri.ToString());
        }

        request.downloadHandler = new DownloadHandlerBuffer();

        yield return request.SendWebRequest();

        if (request.result != UnityWebRequest.Result.Success)
        {
            Debug.LogError("下载文件失败！");
            yield break;
        }

        isDownloading = true;

        // 启动协程来写入文件
        StartCoroutine(WriteToFile());
    }

    IEnumerator WriteToFile()
    {
        using (FileStream fs = new FileStream(savePath, FileMode.Append))
        {
            byte[] data = request.downloadHandler.data;
            fs.Write(data, 0, data.Length);
            bytesDownloaded += data.Length;

            while (isDownloading)
            {
                yield return new WaitForSeconds(0.1f);
                data = request.downloadHandler.data;

                if (data != null && data.Length > 0)
                {
                    fs.Write(data, 0, data.Length);
                    bytesDownloaded += data.Length;
                }

                progress = (float)bytesDownloaded / fileSize;

                if (bytesDownloaded >= fileSize)
                {
                    isDownloading = false;
                    Debug.Log("文件下载完成！");
                    yield break;
                }
            }
        }
    }

    void OnGUI()
    {
        GUI.HorizontalScrollbar(progressRect, 0, progress, 0, 1);
    }
}

在这个示例中，我们首先通过发送HEAD请求来获取文件大小，然后设置Range头字段来支持断点续传。我们使用了DownloadHandlerBuffer来下载文件，并使用FileStream来将下载的数据写入文件。我们还使用了一个协程来检查下载进度，并在GUI上显示进度条。如果下载完成，则停止显示进度条。