我如何向用户报告问题，并且问题正在再次尝试？并且我应该像现在那样重新设置所有内容并再次调用Init（）来执行此操作，还是应该使用计时器并等待几秒钟再尝试一次？
在课堂上我做了：
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.IO;
using System.Net;
using System.Xml;
using HtmlAgilityPack;
using System.ComponentModel;
namespace TestingDownloads
{
class ExtractImages
{
static WebClient client;
static string htmltoextract;
public static List<string> countriescodes = new List<string>();
public static List<string> countriesnames = new List<string>();
public static List<string> DatesAndTimes = new List<string>();
public static List<string> imagesUrls = new List<string>();
static string firstUrlPart = "http://www.sat24.com/image2.ashx?region=";
static string secondUrlPart = "&time=";
static string thirdUrlPart = "&ir=";
public class ProgressEventArgs : EventArgs
{
public int Percentage { get; set; }
public string StateText { get; set; }
}
public event EventHandler<ProgressEventArgs> ProgressChanged;
public void Init()
{
object obj = null;
int index = 0;
ExtractCountires();
foreach (string cc in countriescodes)
{
// raise event here
ProgressChanged?.Invoke(obj,new ProgressEventArgs{ Percentage = 100 * index / countriescodes.Count, StateText = cc });
ExtractDateAndTime("http://www.sat24.com/image2.ashx?region=" + cc);
index +=1;
}
ImagesLinks();
}
public void ExtractCountires()
{
try
{
htmltoextract = "http://sat24.com/en/?ir=true";//"http://sat24.com/en/";// + regions;
client = new WebClient();
client.DownloadFile(htmltoextract, @"c:\temp\sat24.html");
client.Dispose();
string tag1 = "<li><a href=\"/en/";
string tag2 = "</a></li>";
string s = System.IO.File.ReadAllText(@"c:\temp\sat24.html");
s = s.Substring(s.IndexOf(tag1));
s = s.Substring(0, s.LastIndexOf(tag2) + tag2.ToCharArray().Length);
s = s.Replace("\r", "").Replace("\n", "").Replace(" ", "");
string[] parts = s.Split(new string[] { tag1, tag2 }, StringSplitOptions.RemoveEmptyEntries);
string tag3 = "<li><ahref=\"/en/";
for (int i = 0; i < parts.Length; i++)
{
if (i == 17)
{
//break;
}
string l = "";
if (parts[i].Contains(tag3))
l = parts[i].Replace(tag3, "");
string z1 = l.Substring(0, l.IndexOf('"'));
if (z1.Contains("</ul></li><liclass="))
{
z1 = z1.Replace("</ul></li><liclass=", "af");
}
countriescodes.Add(z1);
countriescodes.GroupBy(n => n).Any(c => c.Count() > 1);
string z2 = parts[i].Substring(parts[i].LastIndexOf('>') + 1);
if (z2.Contains("&"))
{
z2 = z2.Replace("&", " & ");
}
countriesnames.Add(z2);
countriesnames.GroupBy(n => n).Any(c => c.Count() > 1);
}
}
catch (Exception e)
{
if (countriescodes.Count == 0)
{
countriescodes = new List<string>();
countriesnames = new List<string>();
DatesAndTimes = new List<string>();
imagesUrls = new List<string>();
Init();
}
}
}
public void ExtractDateAndTime(string baseAddress)
{
try
{
var wc = new WebClient();
wc.BaseAddress = baseAddress;
HtmlDocument doc = new HtmlDocument();
var temp = wc.DownloadData("/en");
doc.Load(new MemoryStream(temp));
var secTokenScript = doc.DocumentNode.Descendants()
.Where(e =>
String.Compare(e.Name, "script", true) == 0 &&
String.Compare(e.ParentNode.Name, "div", true) == 0 &&
e.InnerText.Length > 0 &&
e.InnerText.Trim().StartsWith("var region")
).FirstOrDefault().InnerText;
var securityToken = secTokenScript;
securityToken = securityToken.Substring(0, securityToken.IndexOf("arrayImageTimes.push"));
securityToken = secTokenScript.Substring(securityToken.Length).Replace("arrayImageTimes.push('", "").Replace("')", "");
var dates = securityToken.Trim().Split(new string[] { ";" }, StringSplitOptions.RemoveEmptyEntries);
var scriptDates = dates.Select(x => new ScriptDate { DateString = x });
foreach (var date in scriptDates)
{
DatesAndTimes.Add(date.DateString);
}
}
catch
{
countriescodes = new List<string>();
countriesnames = new List<string>();
DatesAndTimes = new List<string>();
imagesUrls = new List<string>();
this.Init();
}
}
public class ScriptDate
{
public string DateString { get; set; }
public int Year
{
get
{
return Convert.ToInt32(this.DateString.Substring(0, 4));
}
}
public int Month
{
get
{
return Convert.ToInt32(this.DateString.Substring(4, 2));
}
}
public int Day
{
get
{
return Convert.ToInt32(this.DateString.Substring(6, 2));
}
}
public int Hours
{
get
{
return Convert.ToInt32(this.DateString.Substring(8, 2));
}
}
public int Minutes
{
get
{
return Convert.ToInt32(this.DateString.Substring(10, 2));
}
}
}
public void ImagesLinks()
{
int cnt = 0;
foreach (string countryCode in countriescodes)
{
cnt++;
for (; cnt < DatesAndTimes.Count(); cnt++)
{
string imageUrl = firstUrlPart + countryCode + secondUrlPart + DatesAndTimes[cnt] + thirdUrlPart + "true";
imagesUrls.Add(imageUrl);
if (cnt % 10 == 0) break;
}
}
}
}
}
在我使用try和catch的两种情况下，如果要捕获，我将通过重置Lists并再次调用Init（）来尝试整个操作。
然后在form1中
ExtractImages ei = new ExtractImages();
public Form1()
{
InitializeComponent();
ProgressBar1.Minimum = 0;
ProgressBar1.Maximum = 100;
backgroundWorker1.RunWorkerAsync();
}
背景工作者的事件
private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
{
if (backgroundWorker1.CancellationPending == true)
{
e.Cancel = true;
return; // this will fall to the finally and close everything
}
else
{
ei.ProgressChanged += (senders, eee) => backgroundWorker1.ReportProgress(eee.Percentage, eee.StateText);
ei.Init();
}
}
private void backgroundWorker1_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
ProgressBar1.Value = e.ProgressPercentage;
label7.Text = e.UserState.ToString();
label8.Text = e.ProgressPercentage + "%";
}
private void backgroundWorker1_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
if (e.Error == null)
{
ProgressBar1.Value = 100;
}
else
{
}
}
另一件事不确定是否有问题。当类没有问题时，我会在label7的form1中看到所有从头到尾运行的代码。但是progressBar1.Value和label8都只达到了97％，所以我需要在完成的事件中添加progressBar1.Value = 100;。可以吗？班上的报告计算是否有问题？
对于第一个问题：更好地在客户端捕获异常并显示错误消息，因为当某事出错时，您可能需要控制程序的行为。考虑一下：根据您的代码，如果页面的DOM结构更改了，您的程序可能会抛出期望，每个异常都被捕获client.DownloadFile一次，如果发生这种情况，您将需要知道出了什么问题，如果您不更改代码行为，则此类高频率客户端。DownloadFile执行将导致网站的防火墙阻止ip一段时间。我认为在客户端添加计时器是一个好主意。
对于第二个问题：您是否定义了如何处理RunWorkerCompleted事件？
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我来说两句