Checking to see if Html Input textfield has value - asp.net-mvc

Question

On my asp.net web app (mvc), I am wanting to check if the user entered a value in the text field when the button is clicked, and if it is to redirect to the next page. If not, to throw an exception. I looked up on how to do so, and attempted to use it with Html.BeginForm() but for some reason it still does enter my condition statement when I leave the textbox blank and hit the submit button.
ORIGINAL CODE:
SecondController:
[HttpPost]
public IActionResult Insert(String inputF)
{
if (inputF == null)
{
throw new Exception("You did not type anything in the textfield!!!!");
}
else
{
return RedirectToAction("FinalIndex", "Final");
}
}
I wanted it to throw an exception but not stop the program for proceeding like it return a message to the user in the UI but still record the exception that was made.
UPDATED CODE:
My SecondController:
[HttpPost]
public IActionResult Insert(String inputF)
{
if (!ModelState.IsValid || String.IsNullOrWhiteSpace(inputF.Input))
{
return View(inputF);
}
else
{
return RedirectToAction("FinalIndex", "Final");
}
}
It does not let me do String.IsNullOrWhiteSpace(inputF.Input) because it shows the following:
So I then removed the .Input from inputF.Input and it still gave me the the unhandled message in the picture below
My View:
#using CustomerSimulatorApp.Models
#model TextInput
<h2>Second page</h2>
#using (Html.BeginForm("Insert", "Second", FormMethod.Post))
{
#Html.TextBoxFor(r => r.Input);
<input id="Button" type="submit" value="button" />
}
My model:
namespace CustomerSimulatorApp.Models
{
public class TextInput
{
[Required, MinLength(1)]
public String Input { get; set; }
}
}
When I leave the text box empty & hit the button it returns this shown below:
Not sure, if that is what is exactly supposed to happen or if an actual exception was supposed to be thrown. Also, when I just type a single character in the box and hit the button it still allows me to proceed to the redirect and does not throw an exception regardless of my [Required MinLength(2)] on my attribute.
So my objective is to redirect the user to another page (FinalIndex) if the user typed something into the textbox and hits the button. If the user did not type anything in the text box and still hits the button to proceed to the next page, then it needs to throw an exception.
Am I doing something incorrectly? Any suggestions would be greatly appreciated it!

Answer 1

We got this resolved over chat, just had a few naming conventions we changed:
public IActionResult SecIndex(TextInput form)
Was the ultimate fix, instead returning a non-existing view.

Answer 2

You are almost there, but few changes are needed in view and controller side to get it working.
you need to have input button with type submit
#using (Html.BeginForm("Insert", "Second", FormMethod.Post))
{
#Html.TextBoxFor(r => r.Input);
<input id="Button" type="submit" value="button" />
}
and in controller action code should be like:
// this if checks if input textbox value is not present load back page with error
if (!ModelState.IsValid || String.IsNullOrWhiteSpace(inputF.Input))
{
return View(inputF);
}
else
{
// there was value in input redirect to Final controller action
return RedirectToAction("FinalIndex","Final");
}