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Lesson 5618 min read

Working with Forms

Learn how to build HTML forms with Tag Helpers and handle form submissions in ASP.NET Core MVC.

Tag Helpers

Tag Helpers let you write HTML-like syntax that generates the correct markup automatically, tied to your model's properties.

Building a Form

@model TaskDto


<form asp-action="Create" method="post">
    <label asp-for="Title"></label>
    <input asp-for="Title" />
    <span asp-validation-for="Title"></span>


    <label asp-for="Priority"></label>
    <input asp-for="Priority" />


    <button type="submit">Save</button>
</form>

Handling the Submission

[HttpGet]
public IActionResult Create() => View();


[HttpPost]
public IActionResult Create(TaskDto dto)
{
    if (!ModelState.IsValid)
    {
        return View(dto); // redisplay the form with errors
    }


    // save the task...
    return RedirectToAction("Index");
}
Two Actions, One Route

A typical MVC form pattern uses a [HttpGet] action to display the empty form and a separate [HttpPost] action (same name) to handle the submission — this is called the "GET/POST pattern".

Displaying Validation Errors

`<span asp-validation-for="Title"></span>` automatically displays any validation error for that specific field, driven by the same data annotations from the Model Binding & Validation lesson.

FAQs

It sends the browser an HTTP redirect to another action — commonly used after a successful form POST, to avoid resubmitting the form if the user refreshes the page (the Post/Redirect/Get pattern).

Summary

  • Tag Helpers (asp-for, asp-action) generate form markup tied to your model.
  • A typical form uses separate GET (display) and POST (handle) actions.
  • RedirectToAction after a successful POST avoids duplicate form submissions.
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Entity Framework Core Introduction