CloudBlob.EndCopyFromBlob Method

static void CopyBlobConditionallyAsync(Uri blobEndpoint, string accountName, string accountKey)
{
    // Create service client for credentialed access to the Blob service.
    CloudBlobClient blobClient = new CloudBlobClient(blobEndpoint, accountName, accountKey);

    // Create a new blob by uploading a file.
    CloudBlob sourceBlob = blobClient.GetBlobReference("mycontainer/sourceblob.txt");
    sourceBlob.UploadFile("C:\\somefile.txt");

    // Get a reference to the destination blob.
    CloudBlob destBlob = blobClient.GetBlobReference("mycontainer/destblob.txt");

    // Establish an access condition, so that the blob will be copied if the source blob
    // has not been changed in the past hour.
    BlobRequestOptions options = new BlobRequestOptions();
    options.CopySourceAccessCondition = AccessCondition.IfNotModifiedSince(DateTime.Now.AddHours(-1));

    destBlob.BeginCopyFromBlob(sourceBlob, options, CopyBlobCallback, destBlob);
}

static void CopyBlobCallback(IAsyncResult result)
{
    CloudBlob blobDest = (CloudBlob)result.AsyncState;

    // End the operation, checking for the exception that indicates the condition was not met.
    try
    {
        blobDest.EndCopyFromBlob(result);
    }
    catch (StorageClientException e)
    {
        if (e.StatusCode == HttpStatusCode.PreconditionFailed)
        {
            Console.WriteLine("Access condition on source blob not met for blob copy operation.");
        }
        else
        {
            Console.WriteLine("Error code: " + e.ErrorCode);
        }
    }
}