file upload in mvc

Create a ViewModel that includes both the collection of FileModel and the document type dropdown. Then, you can bind the dropdown to a property in the ViewModel.

public class FileViewModel
{
    public IEnumerable Files { get; set; }
    public string SelectedDocumentType { get; set; }
}

@model TestCoreAppTest.ViewModels.FileViewModel

@using (Html.BeginForm("UploadFile", "Home", FormMethod.Post, new { enctype = "multipart/form-data" }))
{
    @Html.DropDownListFor(model => model.SelectedDocumentType, listItems, "-- Select Document Type --")

    
    
}

The root cause behind that is, since you defined the @model IEnumerable in the View,  the View is expecting the collection of FileModel, possibly it might not been initialised in controller with list of FileModel items.

The fundamental problem could be the way of definfing the model, again its depends on the requirement and the UI design, if your are trying to upload a single file to server at a time you can simply define the model like below in your .cshtml file, hence your issue will be resolved

@model TestCoreAppTest.Models.FileModel 

Your final code would be like below

@model TestCoreAppTest.Models.FileModel

@{ 
  var listItems = new List 
    { new SelectListItem { Text = "Legal", Value = "Legal" }, 
      new SelectListItem { Text = "Normal", Value = "Normal" } 
    }; 
} 


@Html.DropDownListFor(model => model.DocType, listItems, "-- Select Document Type --")



 public class FileModel
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public string ContentType { get; set; }
        public byte[] Data { get; set; }

        public string DocType{ get; set; }
    }

now the application on start gives this error 

InvalidOperationException: Sequence contains no elements

• System.Linq.ThrowHelper.ThrowNoElementsException()
• System.Linq.Enumerable.First(IEnumerable source)
• lambda_method13(Closure , IEnumerable )
• Microsoft.AspNetCore.Mvc.ViewFeatures.ExpressionMetadataProvider+<>c__DisplayClass0_0.g__modelAccessor|0(object container)
• Microsoft.AspNetCore.Mvc.ViewFeatures.ModelExplorer.get_Model()
• Microsoft.AspNetCore.Mvc.ViewFeatures.DefaultHtmlGenerator.GetCurrentValues(ViewContext viewContext, ModelExplorer modelExplorer, string expression, bool allowMultiple)
• Microsoft.AspNetCore.Mvc.ViewFeatures.DefaultHtmlGenerator.GenerateSelect(ViewContext viewContext, ModelExplorer modelExplorer, string optionLabel, string expression, IEnumerable selectList, bool allowMultiple, object htmlAttributes)
• Microsoft.AspNetCore.Mvc.ViewFeatures.HtmlHelper.GenerateDropDown(ModelExplorer modelExplorer, string expression, IEnumerable selectList, string optionLabel, object htmlAttributes)
• Microsoft.AspNetCore.Mvc.ViewFeatures.HtmlHelper.DropDownListFor(Expression> expression, IEnumerable selectList, string optionLabel, object htmlAttributes)
• Microsoft.AspNetCore.Mvc.Rendering.HtmlHelperSelectExtensions.DropDownListFor(IHtmlHelper htmlHelper, Expression> expression, IEnumerable selectList, string optionLabel)
• AspNetCore.Views_Home_Index.b__15_2() in Index.cshtml +
  1. @Html.DropDownListFor(model => model.First().doctype, listItems, "-- Select Document Type --")

To resolve the issue with the doctype property not being recognized in the Razor view, you need to ensure that the property is correctly defined in the model and accessed in the view. When using @Html.DropDownListFor, the property should be of a type that can hold the selected value from the dropdown, such as a string or an enum.

public class FileModel
{
    public int Id { get; set; }
    public string Name { get; set; }
    public string ContentType { get; set; }
    public byte[] Data { get; set; }
    public string Doctype { get; set; } // Corrected property name to follow C# naming conventions
}

@model IEnumerable

@{
    var listItems = new List
    {
        new SelectListItem { Text = "Legal", Value = "Legal" },
        new SelectListItem { Text = "Normal", Value = "Normal" }
    };
}

@Html.DropDownListFor(model => model.First().Doctype, listItems, "-- Select Document Type --")

By ensuring that the property name in the model matches the one used in the Razor view and providing the correct type for the dropdown selection, you should be able to display and select document types successfully in your project.