c# - C#无法查看有关API响应的错误，仅抛出异常以尝试/捕获

Question

我正在编写一个程序来检查凭证编号是否有效，并且发现很难从正在使用的REST API中提取错误消息。
C#对我来说像通常的VB.net一样是很新的东西，但是现在可以覆盖某人。
基本上，我有一个HttpWebReqest和HttpWebResponse对象，使用下面的代码，我成功地发出了请求并得到了很好的响应。
当一切顺利时，就没有问题了，但是例如，如果凭单无效或网站无效，我应该得到答复，就像在 postman 中所做的那样，例如，参见下文。

{
    "message": "The given data was invalid.",
    "errors": {
        "voucher_no": [
            "Sorry, that voucher number is invalid."
        ]
    }
}

相反，我被抛出带有异常的Try/Catch ..

Error Message Error 422 unprocessable entity,

没有进一步的细节或对象来检查上面的真实消息？

try
{
    using (HttpWebResponse response = mywebrequest.GetResponse() as HttpWebResponse)
    {
        if (response.StatusCode != HttpStatusCode.OK)
        {
            // I am unable to get to this part of the Code to process the Error because Try/Catch is executed instead ...
        }
        else
        {
            Stream dataStream1 = response.GetResponseStream();
            StreamReader reader = new StreamReader(dataStream1);
            responseFromServer = reader.ReadToEnd();
        }
    }
}
catch (WebException ex)
{
    msgbox = new MsgBox_UI("Error", "Web Server Returned an Error", "There is a problem with this Voucher. It may be Expired or invalid at this time.", 1, false, 28);
    msgbox.ShowDialog();
    break;
}

如果那里有人对我如何进行这项工作有任何想法，那将是很大的帮助。

Answer 1

首先，最好使用HttpClient类。
此代码应为您工作(如果不让我知道):

private async Task<string> GetExtensionToken()
{
    string url = "https://YourApi.com";
    try
    {
        var httpclient = new HttpClient();
        using (HttpResponseMessage response =  httpclient.GetAsync(url).Result)
        {
            using (HttpContent content = response.Content)
            {
                string result =  content.ReadAsStringAsync().Result;
                string Is_Not_Valid = "invalid";
                if (result.Contains(Is_Not_Valid))
                {
                    string token = "Whatever you want to extract if error page" ;
                    return token;
                }
                else
                {
                    string token = "Whatever you want to extract if succeeded" ; return token;
                }
            }
        }
    }
    catch (Exception ex)
    {
        return "Error from catch ";
    }
}

用法:

private async void button1_Click(object sender, EventArgs e)
{
    richTextBox1.Text = await GetExtensionToken();
}