对象引用未设置为对象amazon s3的实例

Question

这是我创建的一个简单的类：

public delegate void ChangeEventHandler(object sender, UploadEventArgs e);

public class UploadEventArgs : EventArgs
{
    public string FileName;
    public string OldFileName;
    //public string ThumbnailName;
    public string ContentType;
    public int ContentLength;
}

public class Bucket
{

    #region Events

    public event ChangeEventHandler OnStart;
    public event ChangeEventHandler OnComplete;
    public event ChangeEventHandler OnError;

    #endregion

    #region Fields

    private string _key;
    private string _secret;
    private const string _seviceUrl = "s3-eu-west-1.amazonaws.com";

    #endregion

    #region Properties

    public string BucketName { get; set; }

    #endregion

    #region Constructors

    public Bucket(string key, string secret)
    {
        this._key = key;
        this._secret = secret;
    }

    public Bucket(string key, string secret, string bucketName)
    {
        this._key = key;
        this._secret = secret;
        this.BucketName = bucketName;
    }

    #endregion

    #region Public methods

    /// <summary>
    /// Creates a bucket in the default EUWest1 region endpoint
    /// </summary>
    /// <param name="bucketName">The name of the new bucket</param>
    public void Create(string bucketName)
    {
        Create(bucketName, RegionEndpoint.EUWest1);
    }

    /// <summary>
    /// Creates a bucket in the specified region endpoint
    /// </summary>
    /// <param name="bucketName">The name of the new bucket</param>
    /// <param name="region">The region endpoint of the bucket</param>
    public void Create(string bucketName, RegionEndpoint region)
    {
        using (var client = Amazon.AWSClientFactory.CreateAmazonS3Client(region))
        {
            // Creates the bucket.
            S3DirectoryInfo rootDirectory = new S3DirectoryInfo(client, bucketName);
            rootDirectory.Create();
        }
        this.BucketName = bucketName; // Set our bucketname property
    }

    public string UploadMultipartFile(HttpPostedFile file)
    {
        if (string.IsNullOrEmpty(BucketName))
            throw new Exception("The bucketname must be supplied."); // Throw an exception if the bucketname has not been initiated

        string keyName = Guid.NewGuid().ToString() + Path.GetExtension(file.FileName);

        UploadEventArgs e = new UploadEventArgs()
        {
            FileName = keyName,
            OldFileName = file.FileName,
            ContentType = file.ContentType,
            ContentLength = file.ContentLength
        };

        try
        {
            OnStart(this, e);
        }
        catch (Exception ex)
        {
        }

        var config = new AmazonS3Config()
        {
            ServiceURL = _seviceUrl
        };
        AmazonS3 client = new AmazonS3Client(_key, _secret, config);

        // List to store upload part responses.
        List<UploadPartResponse> uploadResponses = 
            new List<UploadPartResponse>();

        // 1. Initialize.
        InitiateMultipartUploadRequest initiateRequest = 
            new InitiateMultipartUploadRequest()
            .WithBucketName(BucketName)
            .WithKey(keyName);

        InitiateMultipartUploadResponse initResponse =
            client.InitiateMultipartUpload(initiateRequest);

        // 2. Upload Parts.
        long contentLength = file.InputStream.Length;
        long partSize = 5 * (long)Math.Pow(2, 20); // 5 MB

        try
        {
            long filePosition = 0;
            for (int i = 1; filePosition < contentLength; i++)
            {

                // Create request to upload a part.
                var uploadRequest = new UploadPartRequest()
                    .WithBucketName(BucketName)
                    .WithKey(keyName)
                    .WithUploadId(initResponse.UploadId)
                    .WithPartNumber(i)
                    .WithPartSize(partSize)
                    .WithFilePosition(filePosition)
                    .WithInputStream(file.InputStream);

                // Upload part and add response to our list.
                uploadResponses.Add(client.UploadPart((UploadPartRequest)uploadRequest));

                filePosition += partSize;
            }

            // Step 3: complete.
            CompleteMultipartUploadRequest completeRequest = 
                new CompleteMultipartUploadRequest()
                .WithBucketName(BucketName)
                .WithKey(keyName)
                .WithUploadId(initResponse.UploadId)
                .WithPartETags(uploadResponses);

            CompleteMultipartUploadResponse completeUploadResponse =
                client.CompleteMultipartUpload(completeRequest);

            OnComplete(this, e); 
        }
        catch (Exception exception)
        {
            Console.WriteLine("Exception occurred: {0}", exception.Message);
            client.AbortMultipartUpload(new AbortMultipartUploadRequest()
                .WithBucketName(BucketName)
                .WithKey(keyName)
                .WithUploadId(initResponse.UploadId));

            OnError(this, e);
        }

        return keyName;
    }

    #endregion

}

我遇到的问题是，当调用“OnStart”时，我收到一条错误，指出“对象引用未设置为对象的实例。”。 我已将委托更改为只将“UploadEventArgs”作为参数，我遇到了同样的问题。 我注释掉了所有未使用的属性，但我仍然收到错误。

我知道这是非常简单的事情，但我看不到木头的树木......

任何帮助将不胜感激...... / r3plica