@Html.TextBoxFor with @Value

Question

I am in the process of learning some ASP.NET and now I have a problem that is not helping me despite intensive searching...

I have a view in which I generate a textbox (See My View): Basically, no value is displayed in the text box... even with “@Value = ‘Example’ it remains empty... However, the property @databaseSetup.DatabaseName contains “Test Database”.

Does anyone have any advice on what I am doing wrong?

My View:

@using TestProject.Models
@model DatabaseSetup;
@{
    DatabaseSetup databaseSetup = new();
}
<h1>Database Setup</h1>
@using (Html.BeginForm("DatabaseSetup", "Administration", FormMethod.Post))
{
    <span>Database-Name:</span> 
    
    @Html.TextBoxFor(
        databaseSetup => databaseSetup.DatabaseName,
            new
            {
                @Value = databaseSetup.DatabaseName ?? "127.0.0.1",
                placeholder = "PLACEHOLDER"
            }
    )

My Controller: namespace TestProject.Controllers { public class AdministrationController : Controller {

    public ActionResult DatabaseSetup()
    {
        return View();
    }
    [HttpPost]
    public ActionResult DatabaseSetup(DatabaseSetup u)
    {
        return View(u);
    }
}

}

My Model: namespace TestProject.Models { public class DatabaseSetup { public string DatabaseName { get; set; } = "Test Database"; } }

Even if I proceed in this way, the text box remains empty i.e. the placeholder is displayed...

    @Html.TextBoxFor(
        databaseSetup => databaseSetup.DatabaseName,
            new
            {
                @Value = "Write something",
                placeholder = "PLACEHOLDER"
            }
    )

Answer 1

Model-binding in asp.net-core is not simply searching everywhere for model. It maps the http request data through actions. So in your code you are binding a model initialized in view instead of passed from controller.

Html-Helper works like Tag-Helper that they both retrieve data from model state first. So even if your properties is not empty in the view, it is empty in the model state. https://www.exceptionnotfound.net/modelstate-values-override-model-values-in-htmlhelpers/ https://learn.microsoft.com/en-us/aspnet/core/mvc/views/working-with-forms?view=aspnetcore-8.0#the-input-tag-helper

You need to pass the data from controller to make it work.

@Html.TextBoxFor(
    model => model.DatabaseName,
        new
        {
            //Value = "Write something",
            placeholder = "PLACEHOLDER"
        }
)

Controller

public IActionResult DatabaseSetup()
{
    DatabaseSetup model = new DatabaseSetup();
    return View(model);
    //return View();
}