Azure 存储 Blob 下载进度指示器

Question

下载 blob 时我需要一个进度指示器。

上传时进度指示器已经工作。我在 BlobUploadOptions 中使用 Progresshandler。

BlobDownloadDetails 似乎有进度状态。但是，我不知道如何集成它以使其工作。

这是我的代码：

IKeyEncryptionKey key;
IKeyEncryptionKeyResolver keyResolver;

// Create the encryption options to be used for upload and download.
ClientSideEncryptionOptions encryptionOptions = new ClientSideEncryptionOptions(ClientSideEncryptionVersion.V1_0)
{
   KeyEncryptionKey = key,
   KeyResolver = keyResolver,
   // string the storage client will use when calling IKeyEncryptionKey.WrapKey()
   KeyWrapAlgorithm = "some algorithm name"
};

// Set the encryption options on the client options
BlobClientOptions options = new SpecializedBlobClientOptions() { ClientSideEncryption = encryptionOptions };

// Get your blob client with client-side encryption enabled.
// Client-side encryption options are passed from service to container clients, and container to blob clients.
// Attempting to construct a BlockBlobClient, PageBlobClient, or AppendBlobClient from a BlobContainerClient
// with client-side encryption options present will throw, as this functionality is only supported with BlobClient.
BlobClient blob = new BlobServiceClient(connectionString, options).GetBlobContainerClient("myContainer").GetBlobClient("myBlob");

        BlobUploadOptions uploadOptions = new BlobUploadOptions();
        uploadOptions.ProgressHandler = new Progress<long>(percent =>
        {
           progressbar.Maximum = 100;
           progressbar.Value = Convert.ToInt32(percent * 100 / file.Length);
        });

// Upload the encrypted contents to the blob.
blob.UploadAsync(content: stream, options: uploadOptions, cancellationToken: CancellationToken.None);

// Download and decrypt the encrypted contents from the blob.
MemoryStream outputStream = new MemoryStream();
blob.DownloadTo(outputStream);

Answer 1

目前，DownloadTo 方法不支持进度监视器。查看源码时，DownloadTo 方法定义在BlobBaseClient 类中，而UploadAsync 方法定义在BlobClient 类中，而BlobClient 类继承自BlobBaseClient 类。所以我认为他们可能会错过基类BlobBaseClient中的这个功能。

但是有一个变通方法，代码如下：

class Program
{
    static void Main(string[] args)
    {
        var connectionString = "DefaultEndpointsProtocol=https;AccountName=xx;AccountKey=xxx;EndpointSuffix=core.windows.net";
        BlobServiceClient blobServiceClient = new BlobServiceClient(connectionString);
        BlobContainerClient blobContainerClient = blobServiceClient.GetBlobContainerClient("xxx");
        BlobClient blobClient = blobContainerClient.GetBlobClient("xxx");

        var blobToDownload = blobClient.Download().Value;
        
        MemoryStream outputStream = new MemoryStream();

        var downloadBuffer = new byte[81920];
        int bytesRead;
        int totalBytesDownloaded = 0;

        while ((bytesRead = blobToDownload.Content.Read(downloadBuffer, 0, downloadBuffer.Length)) != 0)
        {
            outputStream.Write(downloadBuffer, 0, bytesRead);
            totalBytesDownloaded += bytesRead;
            Console.WriteLine(GetProgressPercentage(blobToDownload.ContentLength, totalBytesDownloaded));
        }

        Console.WriteLine("**completed**");
        Console.ReadLine();
    }

    private static double GetProgressPercentage(double totalSize, double currentSize)
    {
        return (currentSize / totalSize) * 100;
    }
}

这里是reference doc。