How to capture the URL input and append it to a text box in razor pages?

Question

I am just starting out in razor pages and I need some help with getting the user's inputted URL on a submit and appending it to a local text file. This is for testing purposes, I know it is not common practice to append to a text file.

Here is my html/razor page

@page
@model UploadModel
@{
    ViewData["Title"] = "Upload a Link";
 }
 <h2>@ViewData["Title"]</h2>
 <h3>@Model.Message</h3>

 <form method="post">
   <div class="textBox">
       <input type="url" data-val="true" data-val-url="The Website field is not a valid fully- 
           qualified http, https, or ftp URL." id="input_URL" name="inputURL" value="" />
    <br />
    <button id="submit" type="submit" value="Submit" onclick="btnSubmit_Click()" 
      class="btn btn-primary" runat="server">Submit</button>
   </div>
 </form>

My C#/backend code

   public class urlClass
{
    [BindProperty]
    public string userInput { get; set; }

    private void OnPost()//btnSubmit_Click(object sender, EventArgs e)
    {
        using (StreamWriter writerURL = new StreamWriter("log.txt"))
        {
            urlClass urlc = new urlClass();
            urlc.userInput = ;
            writerURL.WriteLine(urlc.userInput);
        }
    }
}

}

Answer 1

You can try to change userInput to inputURL.Because .net core bind model with name.And you can change private void OnPost() to public void OnPost().So that it can be triggered.Here is a working demo:

cshtml:

<form method="post">
    <div class="textBox">
        <input type="url" data-val="true" data-val-url="The Website field is not a valid fully-
           qualified http, https, or ftp URL." id="input_URL" name="inputURL" value="" />
        <br />
        <button id="submit" type="submit" value="Submit" 
                class="btn btn-primary" runat="server">
            Submit
        </button>
    </div>
</form>

cshtml.cs:

[BindProperty]
        public string inputURL { get; set; }

        public void OnPost()//btnSubmit_Click(object sender, EventArgs e)
        {
            using (StreamWriter writerURL = new StreamWriter("log.txt"))
            {
                //urlClass urlc = new urlClass();
                //urlc.userInput = ;
                writerURL.WriteLine(inputURL);
            }
        }

result: