Razor Listbox help

Question

User-507786106 posted

I have a listbox I my code below, I need to add the model Values  StudentList is empty, how do I check for empty listbox?

Problem:  Null StudentList fails or causes null error. My code could be constructed incorrectly....

ViewBag.StudentList  <--- has 10 records

List<MessageCenterModel> objData = new List<MessageCenterModel>

foreach (var item in ViewBag.StudentList)

{

       MessageCenterModel  obj = new MessageCenterModel();

      objData.StudentList.Add   <---- I get lost here -- How can I add the values and text here

}

Model Code has

public List<SelectListItem> StudentList {get; set;}

Answer 1

User475983607 posted

One issue is the ViewBag must be cast to the proper type.  

foreach (var item in (List<SelectListItem>)ViewBag.StudentList )

The other issue is, you are trying to add a SelectListItem type to a List<MessageCenterModel>.  

Can you explain what you are trying to do here?  It seems you could just use an Html helper to populate a listbox.

Answer 2

User-1038772411 posted

Hello, Slimbunny

Simply you can use below code for add model data into selectedListitem.

var lst1 = new List<MessageCenterModel>();
lst1.Add(new MessageCenterModel{ Text1= "text1data",  Text2= "text2data" });
//Checking for Model is null or empty
if(lst1 != null && lst1!=""){
 foreach (var item in lst1)
  {
    StudentList.Add(new SelectListItem() { Value = item.valuename, Text = item.textname });
  }
}

public List<SelectListItem> StudentList { get; } = new List<SelectListItem>();

Thanks.

Answer 3

User665608656 posted

Hi slimbunny,

According to your description,I'm not sure about the relationship between objects in your code.

First, you should judge ViewBag.StudentList is not null,then loop it.

Next,you could try to write this on the basis of your code:

            List<SelectListItem> listSelectListItems = new List<SelectListItem>();           
            foreach (var item in ViewBag.StudentList)
            {
                SelectListItem selectList = new SelectListItem()
                {
                    Text = item.Name,
                    Value = item.ID.ToString(),
                    Selected = item.IsSelected
                };
                listSelectListItems.Add(selectList);
            }

Here's an example of listbox binding data in mvc that you could refer to:

https://www.codeproject.com/articles/771999/asp-net-mvc-how-to-create-a-listbox

Best Regards,

YongQing.