csharp ASP.NET MVC中的DropDownList #dropdownlist #selectlist

Posted 2021-05-12

@model Dropdowns.Models.SignUpModel

@{ ViewBag.Title = "Sign up"; }

<div class="row">
    <div class="col-sm-4 col-sm-offset-4">

        <h1>Sign up</h1>

        <div class="panel panel-default">
            <div class="panel-body">
                @using (Html.BeginForm("SignUp", "SignUp", FormMethod.Post, new { role = "form" })) {

                    @* Name textbox *@
                    <div class="form-group">
                        @Html.LabelFor(m => m.Name)
                        @Html.TextBoxFor(m => m.Name, new { @class = "form-control" })
                    </div>

                    @* State selection dropdown *@
                    <div class="form-group">
                        @Html.LabelFor(m => m.State)
                        @Html.DropDownListFor(m => m.State, // 1. Store selected value in Model.State;
                                                            // when page is rendered after postback,
                                                            // take selected value from Model.State.

                                              // 2. Take list of values from Model.States
                                              Model.States, 

                                              // 3. Text for the first 'default' option
                                              "- Please select a state -", 

                                              //4. A class name to assign to <select> tag
                                              new { @class = "form-control" })
                    </div>

                    <button type="submit" class="btn btn-primary">Sign up</button>
                }
            </div>
        </div>
    </div>
</div>

public class SignUpController : Controller
{
	//
    // 1. Action method for displaying 'Sign Up' page
    //
    public ActionResult SignUp()
    {
    	// Let's get all states that we need for a DropDownList
        var states = GetAllStates();
        
        var model = new SignUpModel();

		// Create a list of SelectListItems so these can be rendered on the page
        model.States = GetSelectListItems(states);

		return View(model);
     }

    //
    // 2. Action method for handling user-entered data when 'Sign Up' button is pressed.
    //
    [HttpPost]
    public ActionResult SignUp(SignUpModel model)
    {
        // Get all states again
        var states = GetAllStates();

        // Set these states on the model. We need to do this because
        // only the selected value from the DropDownList is posted back, not the whole
        // list of states.
        model.States = GetSelectListItems(states);

        // In case everything is fine - i.e. both "Name" and "State" are entered/selected,
        // redirect user to the "Done" page, and pass the user object along via Session
        if (ModelState.IsValid)
        {
            Session["SignUpModel"] = model;
            return RedirectToAction("Done");
        }

        // Something is not right - so render the registration page again,
        // keeping the data user has entered by supplying the model.
        return View("SignUp", model);
    }

    //
    // 3. Action method for displaying 'Done' page
    //
    public ActionResult Done()
    {
        // Get Sign Up information from the session
        var model = Session["SignUpModel"] as SignUpModel;

        // Display Done.html page that shows Name and selected state.
        return View(model);
    }

    // Just return a list of states - in a real-world application this would call
    // into data access layer to retrieve states from a database.
    private IEnumerable<string> GetAllStates()
    {
        return new List<string>
        {
            "ACT",
            "New South Wales",
            "Northern Territories",
            "Queensland",
            "South Australia",
            "Victoria",
            "Western Australia",
        };
    }

    // This is one of the most important parts in the whole example.
    // This function takes a list of strings and returns a list of SelectListItem objects.
    // These objects are going to be used later in the SignUp.html template to render the
    // DropDownList.
    private IEnumerable<SelectListItem> GetSelectListItems(IEnumerable<string> elements)
    {
        // Create an empty list to hold result of the operation
        var selectList = new List<SelectListItem>();

        // For each string in the 'elements' variable, create a new SelectListItem object
        // that has both its Value and Text properties set to a particular value.
        // This will result in MVC rendering each item as:
        //     <option value="State Name">State Name</option>
        foreach (var element in elements)
        {
            selectList.Add(new SelectListItem
            {
                Value = element,
                Text = element
            });
        }

        return selectList;
    }
}

public class SignUpModel
{
  [Required]
  [Display(Name="Name")]
  public string Name { get; set; }

  // This property will hold a state, selected by user
  [Required]
  [Display(Name="State")]
  public string State { get; set; }

  // This property will hold all available states for selection
  public IEnumerable<SelectListItem> States { get; set; }
}