htmlhelper validationmessage ASP.NET MVC

In ASP.NET MVC, the Html.ValidationMessageFor method is used to display validation error messages for a particular model property.

Here's an example of how to use Html.ValidationMessageFor:

1. Create a model class with validation attributes. For example:

public class Person {
   [Required(ErrorMessage = "Please enter your name.")]
   public string Name { get; set; }
   
   [Range(0, 120, ErrorMessage = "Please enter a valid age.")]
   public int Age { get; set; }
}

2. In your controller, create an instance of your model and pass it to the view. For example:

public ActionResult Create() {
   var person = new Person();
   return View(person);
}

[HttpPost]
public ActionResult Create(Person person) {
   if (ModelState.IsValid) {
      // Save person to database
      return RedirectToAction("Index");
   }
   return View(person);
}

3. In your view, use Html.ValidationMessageFor to display validation error messages for each property. For example:

@model Person
@using (Html.BeginForm()) {
   @Html.LabelFor(m => m.Name)
   @Html.TextBoxFor(m => m.Name)
   @Html.ValidationMessageFor(m => m.Name)
   
   @Html.LabelFor(m => m.Age)
   @Html.TextBoxFor(m => m.Age)
   @Html.ValidationMessageFor(m => m.Age)
   
   <input type="submit" value="Save" />
}

The Html.ValidationMessageFor method will automatically generate an error message based on the validation attributes you specified in your model class. If the model validation fails, the error message will be displayed next to the corresponding form field.