使用收益率延迟Azure blob存储调用-c#

我目前有一个方法，可以从Azure中提取blob文件名列表。方法如下：

internal async Task<IEnumerable<BlobItem>> GetFiles(CloudBlobContainer container, string directoryName, bool recursive)
{
    var results = new List<BlobItem>();
    BlobContinuationToken continuationToken = null;

    do
    {
        var response = await container.GetDirectoryReference(directoryName).ListBlobsSegmentedAsync(false, BlobListingDetails.None, 100, continuationToken, null, null);

        continuationToken = response.ContinuationToken;
        foreach (var item in response.Results)
        {
            if (item.GetType() != typeof(CloudBlobDirectory))
                results.Add(new BlobItem(item));
            else if (recursive)
                results.AddRange(await GetFiles(container, ((CloudBlobDirectory)item).Prefix, recursive));
        }
    }
    while (continuationToken != null);

    return results;
}

---

编辑2018-11-15 从C#8开始，您将能够使用

IAsyncEnumerable

：

async IAsyncEnumerable<int> GetBigResultsAsync()
{
    await foreach (var result in GetResultsAsync())
    {
        if (result > 20) yield return result; 
    }
}

IAsyncEnumerable<string> GetAsyncAnswers()
{
    return AsyncEnum.Enumerate<string>(async consumer =>
    {
        foreach (var question in GetQuestions())
        {
            string theAnswer = await answeringService.GetAnswer(question);
            await consumer.YieldAsync(theAnswer);
        }
    });
}

---

奇怪的是，使用收益法，执行时间从1分24秒（无收益）显著增加到了4分14秒——假设它将事情推迟到需要的时候。这是一个很棒的答案+非常感谢你，亚历克斯！！！我现在可以选择使用“ToEnumerable”或直接订阅“GetFiles”（可观察）。布里尔！！

using Microsoft.WindowsAzure.Storage;
using Microsoft.WindowsAzure.Storage.Blob;

async IAsyncEnumerable<int> GetBigResultsAsync()
{
    await foreach (var result in GetResultsAsync())
    {
        if (result > 20) yield return result; 
    }
}

IAsyncEnumerable<string> GetAsyncAnswers()
{
    return AsyncEnum.Enumerate<string>(async consumer =>
    {
        foreach (var question in GetQuestions())
        {
            string theAnswer = await answeringService.GetAnswer(question);
            await consumer.YieldAsync(theAnswer);
        }
    });
}

public IEnumerable<BlobItem> GetFilesAsEnumerable(CloudBlobContainer container, string directoryName, bool recursive)
{
    return GetFiles(container, directoryName, recursive).ToEnumerable();
}

public IObservable<BlobItem> GetFiles(CloudBlobContainer container, string directoryName, bool recursive)
{
    return Observable.Create<BlobItem>(async obs =>
        {
            BlobContinuationToken continuationToken = null;

            do
            {
                var response = await container.GetDirectoryReference(directoryName).ListBlobsSegmentedAsync(/*useFlatBlobListing*/ recursive, BlobListingDetails.None, 100, continuationToken, null, null);

                continuationToken = response.ContinuationToken;
                foreach (var item in response.Results)
                {
                    // Only required if recursive == false
                    if (item.GetType() != typeof(CloudBlobDirectory))
                        obs.OnNext(new BlobItem(item));
                }
            }
            while (continuationToken != null);
        });
}