ModelState (System.Web.Mvc) with example

ModelState refers to a set of name and value pairs submitted to the server during a post. This allows you to save the value submitted to the server and check for errors associated with each value. Let's see how this works with an example.

The following is a sample model code. It has three properties: MovieID, Movie and Release Year.

SampleViewModel.cs

public class SampleViewModel
{
    public int MovieID { get; set; }
    public string Movie { get; set; }
    public int ReleaseYear { get; set; }
}

Below is an index view code. Here you can see how the model properties are bonded to the TagHelpers.

Index.cshtml

@{
    ViewData["Title"] = "ModelState Example";
    Layout = null;
}

@model SampleViewModel

<form action="/Home/index"  method="post">
    <div>
        <div>
            <label for="MovieID">Movie ID:</label>
            <input id="MovieID" name="MovieID" type="text">
        </div>
        <div>
            <label for="Movie">Movie:</label>
            <input id="Movie" name="Movie" type="text">
        </div>
        <div>
            <label for="ReleaseYear">Release Year:</label>
            <input id="ReleaseYear" name="ReleaseYear" type="text">
        </div>
        <div>
            <input type="submit" value="Save">
        </div>
    </div>
</form>

The following is a controller code. There are two actions involved. The first action passes the SampleViewModel to view, the second obtain a ViewModel with values.

HomeController.cs

public IActionResult Index()
{
    SampleViewModel model = new SampleViewModel();
    return View(model);
}

[HttpPost]
public IActionResult Index(SampleViewModel model)
{
    if (!ModelState.IsValid)
    {
        return View(model);
    }
    return RedirectToAction("Sample");
}

The following screenshot is taken while running the app through the breakpoint in ModelState. In the picture, you can see the properties of the ModelState.

Count: It shows the number of properties in the ModelState. In the screenshot, it has three (MovieIT, Movie and Release Year).

ErrorCount: The number of error added to the ModelState

HasReachedMaxErrors: This is a Boolean value. If ModelState reaches the maximum error it will return to true. That would be true when Microsoft.AspNetCore.Mvc.ModelBinding.TooManyModelErrorsException throws.

IsValid: This is a Boolean. This indicates whether the ModelState values are valid or not.

Keys: It contains the key sequence.

MaxAllowedError: This allows ModelStateDictionary to obtain or set the maximum allowable ModelState errors in this instance. The default value is 200.

Root: It is a root entry for ModelStateDictionary.

Values: It helps to set the value sequence.

I hope this article is helpful to you. Keep coding.