When I click Submit button in form tag, values I have collected in variables when page loaded first are getting erased. I am using In .Net Core MVC.

This is my code

public IActionResult Index(string cap)
{
    var rnumber = ViewData["captcha"];
    if (cap == rnumber)
    {
      Isvisble = "visible";
    }
    randnumber = RandomString(6);
    ViewData["captcha"] = randnumber;
    return View();
}

This is my cshtml code

<form method="get" asp-action="Index">
    <div >
        <h1 >Welcome</h1>
        <label for="captcha"><b>Enter chaptcha -  </b></label>
        <label id="lblCapval" for="captchasym"><b>@ViewData["captcha"]</b></label>
        <input id="txtCapValue" type="text" placeholder="Enter captcha" name="cap" required>
        <br />
        <button  type="submit">Login</button>
    </div>
</form>

Here when I click on submit button, randnumber and ViewData["captcha"] both are null in Index method. How can I retain those values ?

CodePudding user response：

ViewData itself cannot be used to send data from View to Controller. You can use Session instead:

Controller:

public class HomeController : Controller
{
    private readonly ILogger<HomeController> _logger;
    private readonly IHttpContextAccessor _httpContextAccessor;
    private readonly ISession _memorySession;

    public HomeController(ILogger<HomeController> logger, IHttpContextAccessor httpContextAccessor)
    {
        _logger = logger;
        _httpContextAccessor = httpContextAccessor;
        _memorySession = _httpContextAccessor.HttpContext.Session;
    }

    public IActionResult Index(string cap)
    { 
        var rnumber = _memorySession.GetString("captcha");
        if (cap == rnumber)
        {
            Isvisble = "visible";
        }
        string randnumber = RandomString(6);
        _memorySession.SetString("captcha", randnumber);
        return View();
    }
}

View:

@using Microsoft.AspNetCore.Http
@inject IHttpContextAccessor httpContextAccessor
@{
    ViewData["Title"] = "Home Page";
}

<form method="get" asp-action="Index">
    <div >
        <h1 >Welcome</h1>
        <label for="captcha"><b>Enter chaptcha -  </b></label>
        <label id="lblCapval" for="captchasym"><b>@httpContextAccessor.HttpContext.Session.GetString("captcha")</b></label>
        <input id="txtCapValue" type="text" placeholder="Enter captcha" name="cap" required>
        <br />
        <button  type="submit">Login</button>
    </div>
</form>

Don't forget to register services and middleware:

builder.Services.AddSession();
builder.Services.AddSingleton<IHttpContextAccessor, HttpContextAccessor>();
app.UseSession();

Test Result:

In addition, you need to pay attention that your Index method will enter the RandomString method every time, if you want to save the randnumber, you need to add a judgment condition. For example, the RandomString method is only entered when rnumber==null.

You can also use input to pass ViewData back to the controller as a string:

<input type="hidden" name="captcha" value="@ViewData["captcha"]" />

And your controller:

public IActionResult Index(string cap ,string captcha)
{
    var rnumber = captcha;
}