为什么WebClient

Question

我可以尝试从 url 获取字符串，但是当我执行程序时 GUI 冻结

Answer 1

如果您在 4.5 之前以 .NET 为目标，则没有 async/await - 相反，您可以使用 DownloadStringAsync 的异步版本，它会在下载字符串时引发事件

var client = new WebClient();
client.DownloadStringCompleted += new DownloadStringCompletedEventHandler(DownloadStringCompletedHandler);

for (long i = 1; i < gethow; i++)
{
    string WebAdress = "https://xxxxxx.xxx/web?id=";
    var request = WebAdress + (fromNumber - 1 + i);    

    client.DownloadStringAsync(request);

}

// -- > Elsewhere in your form
void DownloadStringCompletedHandler(object sender, DownloadStringCompletedEventArgs e)
{
    slas = "0" + Convert.ToString((fromNumber - 1 + i));
    if (e.Result == "Test")
    {
        if (!listBox1.Items.Contains(slas))
        {                
             listBox1.Items.Add(slas);
             godn++;
         }
    }
}

如果您的所有代码必须在您的按钮点击中，您可以内联事件处理程序

var client = new WebClient();
client.DownloadStringCompleted += (s,e) => {
    slas = "0" + Convert.ToString((fromNumber - 1 + i));
    if (e.Result == "Test")
    {
        if (!listBox1.Items.Contains(slas))
        {                
             listBox1.Items.Add(slas);
             godn++;
         }
    }
};

for (long i = 1; i < gethow; i++)
{
    string WebAdress = "https://xxxxxx.xxx/web?id=";
    var request = WebAdress + (fromNumber - 1 + i);    

    client.DownloadStringAsync(request);

}

---

编辑：您已将问题中的代码更新为类似于此答案，但您假设 DownloadStringAsync 返回结果 - 它没有。该方法不返回任何内容。字符串在事件处理程序中返回

var client = new WebClient();
client.DownloadStringCompleted += new DownloadStringCompletedEventHandler(DownloadStringCompletedHandler);
result=client.DownloadStringAsync(request); // <-- This line is wrong

应该是

client.DownloadStringAsync(request);

并将DownloadStringCompletedHandler 中的字符串作为e.Result 接收