暂停程序直到获得响应

Question

static string IP_Address = "";
getIPAddress();
MessageBox.Show(IP_Address);

我的功能是这样的：

 public static void getIPAddress()
 {
    Uri uri = new Uri("http://whatismyip.org", UriKind.Absolute);
    WebClient client = new WebClient();

    client.DownloadStringCompleted += (s, e) =>
        {
            var res = e.Result;
            IP_Address = res;
        };
    client.DownloadStringAsync(uri);
 }

我正在使用此代码设置客户端的IP地址。但问题是，当我运行代码时，首先显示的是空字符串IP_Address，然后只显示

client.DownloadStringCompleted += (s, e) =>
        {
            var res = e.Result;
            IP_Address = res;
        };

部分被执行。在显示IP_Address之前运行上述代码块的任何建议。

Answer 1

 getIPAddress((ip) =>
 {
      MessageBox.Show(ip);
 });

 public static void getIPAddress(Action<string> callback)
 {
      Uri uri = new Uri("http://whatismyip.org", UriKind.Absolute);
      WebClient client = new WebClient();

      client.DownloadStringCompleted += (s, e) =>
      {
           var res = e.Result;

           callback(res);
      };
      client.DownloadStringAsync(uri);
 }