从 url 下载文件并转换为 base64 异步 (C#)

Question

我有需要下载文件并转换为 Base64 字符串的 url

我写了这段代码来做到这一点

private string GetImageAsBase64(string url)
    {
        using (var client = new WebClient())
        {
            var bytes = client.DownloadData(url);
            var base64String = Convert.ToBase64String(bytes);
            return base64String;
        }
    }

如何使其异步使用返回类型Task<string>？

Answer 1

你就快到了，使用GetByteArrayAsync：

private async Task<string> GetImageAsBase64Async(string url) // return Task<string>
{
    using (var client = new HttpClient())
    {
        var bytes = await client.GetByteArrayAsync(url); // there are other methods if you want to get involved with stream processing etc
        var base64String = Convert.ToBase64String(bytes);
        return base64String;
    }
}

UPD

正如@Fildor指出的，您希望实例化HttpClient一次并将其注入到函数中。一个非常简单的方法是使用扩展方法：

void Main()
{
    HttpClient client = new HttpClient(); // can reuse
    client.GetImageAsBase64("...");
    client.GetImageAsBase64("...");
    client.GetImageAsBase64("...");
}

static class HttpclientExtensions
{
    public static async Task<string> GetImageAsBase64(this HttpClient client, string url)
    {
        var bytes = await client.GetByteArrayAsync(url);
        return Convert.ToBase64String(bytes);
    }
}