C#停止一个无限foreach循环

本文关键字：一个 无限 foreach 循环 | 更新日期: 2023-09-27 18:25:10

这个foreach循环检查网页，看看是否有图像，然后下载它们。我该如何阻止它？当我按下按钮时，它将永远循环。

 private void button1_Click(object sender, EventArgs e)
    {
        WebBrowser browser = new WebBrowser();
        browser.DocumentCompleted +=browser_DocumentCompleted;
        browser.Navigate(textBox1.Text);           
    }
    void browser_DocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e)
    {
        WebBrowser browser = sender as WebBrowser;
        HtmlElementCollection imgCollection = browser.Document.GetElementsByTagName("img");
        WebClient webClient = new WebClient();
        int count = 0; //if available
        int maximumCount = imgCollection.Count;
        try
        {
                foreach (HtmlElement img in imgCollection)
                {
                    string url = img.GetAttribute("src");
                    webClient.DownloadFile(url, url.Substring(url.LastIndexOf('/')));
                     count++;
                     if(count >= maximumCount)
                          break;
                }
        }
        catch { MessageBox.Show("errr"); }
    }

C#停止一个无限foreach循环

使用break;关键字突破循环

您没有无限循环，您有一个异常，它是根据您将文件写入磁盘的方式抛出的

private void button1_Click(object sender, EventArgs e)
{
    WebBrowser browser = new WebBrowser();
    browser.DocumentCompleted += browser_DocumentCompleted;
    browser.Navigate("www.google.ca");
}
void browser_DocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e)
{
    WebBrowser browser = sender as WebBrowser;
    HtmlElementCollection imgCollection = browser.Document.GetElementsByTagName("img");
    WebClient webClient = new WebClient();
    foreach (HtmlElement img in imgCollection)
    {
        string url = img.GetAttribute("src");
        string name = System.IO.Path.GetFileName(url);
        string path = System.IO.Path.Combine(Environment.CurrentDirectory, name);
        webClient.DownloadFile(url, path);
    }
}

该代码在我的环境中运行良好。您似乎遇到的问题是，当您设置DownloadFile filepath时，您将其设置为类似"''myimage.png"的值，而Web客户端找不到路径，因此引发异常。

上面的代码将其放入具有扩展名的当前目录中。

也许是事件浏览器。DocumentCompleted会导致错误，如果页面刷新，则会再次触发事件。您可以尝试取消注册该事件。

void browser_DocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e)
{    
    WebBrowser browser = sender as WebBrowser;
    browser.DocumentCompleted -= browser_DocumentCompleted;
    HtmlElementCollection imgCollection = browser.Document.GetElementsByTagName("img");
    WebClient webClient = new WebClient();
    foreach (HtmlElement img in imgCollection)
    {
        string url = img.GetAttribute("src");
        string name = System.IO.Path.GetFileName(url);
        string path = System.IO.Path.Combine(Environment.CurrentDirectory, name);
        webClient.DownloadFile(url, path);
    }
}
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