Open multiple pages in WebBrowser and send a command to all of them

Question

I have a winform app with the following functionality:

1. Has a multiline textbox that contain one URL on each line - about 30 URLs (each URL is different but the webpage is the same (just the domain is different);
2. I have another textbox in which I can write a command and a button that sends that command to an input field from the webpage.
3. I have a WebBrowser controller ( I would like to do all the things in one controller )

The webpage consist of a textbox and a button which I want to be clicked after I insert a command in that textbox.

My code so far:

//get path for the text file to import the URLs to my textbox to see them
private void button1_Click(object sender, EventArgs e)
{
    OpenFileDialog fbd1 = new OpenFileDialog();
    fbd1.Title = "Open Dictionary(only .txt)";
    fbd1.Filter = "TXT files|*.txt";
    fbd1.InitialDirectory = @"M:\";
    if (fbd1.ShowDialog(this) == DialogResult.OK)
        path = fbd1.FileName;
}

//import the content of .txt to my textbox
private void button2_Click(object sender, EventArgs e)
{
    textBox1.Lines = File.ReadAllLines(path);
}

//click the button from webpage
private void button3_Click(object sender, EventArgs e)
{
    this.webBrowser1.Document.GetElementById("_act").InvokeMember("click");
}

//parse the value of the textbox and press the button from the webpage
private void webBrowser1_DocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e)
{
    newValue = textBox2.Text;
    HtmlDocument doc = this.webBrowser1.Document;
    doc.GetElementById("_cmd").SetAttribute("Value", newValue);     
}

Now, how can I add all those 30 URLs from my textbox in the same webcontroller so that I can send the same command to all of the textboxes from all the webpages and then press the button for all of them ?

---

//EDIT 1 So, I have adapted @Setsu method and I've created the following:

public IEnumerable<string> GetUrlList()
{
    string f = File.ReadAllText(path); ;
    List<string> lines = new List<string>();

    using (StreamReader r = new StreamReader(f))
    {
        string line;
        while ((line = r.ReadLine()) != null)
            lines.Add(line);
    }
    return lines;
}

Now, is this returning what it should return, in order to parse each URL ?

Answer 1

If you want to keep using just 1 WebBrowser control, you'd have to sequentially navigate to each URL. Note, however, that the Navigate method of the WebBrowser class is asynchronous, so you can't just naively call it in a loop. Your best bet is to implement an async/await pattern detailed in this answer here.

Alternatively, you CAN have 30 WebBrowser controls and have each one navigate on its own; this is roughly equivalent to having 30 tabs open in modern browsers. Since each WebBrowser is doing identical work, you can just have 1 DocumentCompleted event written to handle a single WebBrowser, and then hook up the others to the same event. Do note that the WebBrowser control has a bug that will cause it to gradually leak memory, and the only way to solve this is to restart the application. Thus, I would recommend going with the async/await solution.

UPDATE:

Here's a brief code sample of how to do the 30 WebBrowsers way (untested as I don't have access to VS right now):

List<WebBrowser> myBrowsers = new List<WebBrowser>();

public void btnDoWork(object sender, EventArgs e)
{
    //This method starts navigation.
    //It will call a helper function that gives us a list 
    //of URLs to work with, and naively create as many
    //WebBrowsers as necessary to navigate all of them

    IEnumerable<string> urlList = GetUrlList();
    //note: be sure to sanitize the URLs in this method call

    foreach (string url in urlList)
    {
        WebBrowser browser = new WebBrowser();
        browser.DocumentCompleted += webBrowserDocumentCompleted;
        browser.Navigate(url);
        myBrowsers.Add(browser);
    }
}

private void webBrowserDocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e)
{
    //check that the full document is finished
    if (e.Url.AbsolutePath != (sender as WebBrowser).Url.AbsolutePath) 
        return;

    //get our browser reference
    WebBrowser browser = sender as WebBrowser;

    //get the string command from form TextBox
    string command = textBox2.Text;

    //enter the command string
    browser.Document.GetElementById("_cmd").SetAttribute("Value", command);

    //invoke click
    browser.Document.GetElementById("_act").InvokeMember("click");

    //detach the event handler from the browser
    //note: necessary to stop endlessly setting strings and clicking buttons
    browser.DocumentCompleted -= webBrowserDocumentCompleted;
    //attach second DocumentCompleted event handler to destroy browser
    browser.DocumentCompleted += webBrowserDestroyOnCompletion;
}

private void webBrowserDestroyOnCompletion(object sender, WebBrowserDocumentCompletedEventArgs e)
{
    //check that the full document is finished
    if (e.Url.AbsolutePath != (sender as WebBrowser).Url.AbsolutePath) 
        return;

    //I just destroy the WebBrowser, but you might want to do something
    //with the newly navigated page

    WebBrowser browser = sender as WebBrowser;
    browser.Dispose();
    myBrowsers.Remove(browser);
}