c# - There is no ViewData item of type IEnumerable -

i have viewmodel :

public class foundviewmodel {     public string title { get; set; }     public string description { get; set; }     public int city { get; set; }     public int subgroup { get; set; }     public string address { get; set; }     public datetime finddate { get; set; }  } 

and in view add 2 dropdown , fill in actionresult when call get:

var provinces = _provinces.selectall();        viewbag.provinces = new selectlist(provinces,"id","title",provinces.firstordefault().id); 

and in view :

@html.dropdownlist("drpprovince", (selectlist)viewbag.provinces, new { @onchange="javascript:getcity(this.value);"}) 

but when click on button , post , getting error:

there no viewdata item of type 'ienumerable<selectlistitem>' has key 'drpprovince' 

i found similar question on stackover flow can't know .

what's problem ? thanks.

what happens that, @ time of post , reload page show cities according selected province, not generating viewbag again.

the solution initialize viewbag again since lost after postback each call.

example.

public actionresult loadcities () {     /* logic .... */     // here initialize viewbag again view know.     return view (); }