Asp net mvc dropdownlist retain the selected value in the browser after post

ASP.NET MVC is a powerful framework for building web . One requirement in web is to retain the value of a dropdownlist in the after a postback. In this article, we will explore different approaches to achieve this using ASP.NET MVC.

Approach 1: Using ViewBag

One way to retain the selected value of a dropdownlist is by using the ViewBag in ASP.NET MVC. The ViewBag is a dynamic property that allows us to share data between the controller and the view. Here's an example:


// Controller
public  Index()
{
    ViewBag.Fruits = new SelectList(new[]
    {
        new SelectListItem { Value = "1", Text = "Apple" },
        new SelectListItem { Value = "2", Text = "Banana" },
        new SelectListItem { Value = "3", Text = "Orange" }
    }, "Value", "Text");

    return View();
}

[HttpPost]
public ActionResult Index(string selectedFruit)
{
    ViewBag.Fruits = new SelectList(new[]
    {
        new SelectListItem { Value = "1", Text = "Apple" },
        new SelectListItem { Value = "2", Text = "Banana" },
        new SelectListItem { Value = "3", Text = "Orange" }
    }, "Value", "Text", selectedFruit);

    return View();
}

// View
@Html.DropDownList("selectedFruit", ViewBag.Fruits as SelectList)

In this example, we first populate the dropdownlist in the Index action of the controller using the ViewBag. We pass the selectedFruit value to the SelectList constructor to retain the selected value after a postback. In the view, we use the Html.DropDownList helper to render the dropdownlist.

Approach 2: Using Model

approach to retain the selected value of a dropdownlist is by using model binding in ASP.NET MVC. Model binding automatically maps form to model . Here's an example:


// Model
public class FruitViewModel
{
    public string SelectedFruit { get; set; }
    public SelectList Fruits { get; set; }
}

// Controller
public ActionResult Index()
{
    var model = new FruitViewModel
    {
        Fruits = new SelectList(new[]
        {
            new SelectListItem { Value = "1", Text = "Apple" },
            new SelectListItem { Value = "2", Text = "Banana" },
            new SelectListItem { Value = "3", Text = "Orange" }
        }, "Value", "Text")
    };

    return View(model);
}

[HttpPost]
public ActionResult Index(FruitViewModel model)
{
    model.Fruits = new SelectList(new[]
    {
        new SelectListItem { Value = "1", Text = "Apple" },
        new SelectListItem { Value = "2", Text = "Banana" },
        new SelectListItem { Value = "3", Text = "Orange" }
    }, "Value", "Text", model.SelectedFruit);

    return View(model);
}

// View
@Html.DropDownListFor(model => model.SelectedFruit, Model.Fruits)

In this example, we create a FruitViewModel class that contains the selectedFruit property and the Fruits property. We populate the dropdownlist in the Index action of the controller using the FruitViewModel. The selectedFruit property is automatically bound to the dropdownlist value after a postback. In the view, we use the Html.DropDownListFor helper to render the dropdownlist.

Conclusion

Retaining the selected value of a dropdownlist in the browser after a postback is a common requirement in web development. In this article, we explored two approaches to achieve this using ASP.NET MVC. The first approach uses the ViewBag to share data between the controller and the view, while the second approach uses model binding to automatically map form values to model properties. Both approaches are effective and can be used based on the specific requirements of your application.

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