asp.net mvc - MVC3 EditorFor losing value on postback -

i've created , date editorfor template value getting lost on postback. please can help?

here's date.cshtml stored in 'shared/editortemplates' folder:

    @model datetime  <div class="input-append">     <input type="text" class="input-small datepicker" id="@viewbag.id" name="@viewbag.id" />     <span class="add-on"><i class="icon-th"></i></span> </div> 

here's view:

@html.editorfor(m => m.requiredbydate, new { id = "requiredbydate" }) 

and property on viewmodel:

    [display(name = "required date")] [required(errormessage = "required date required.")] [datatype(datatype.date)] public datetime requiredbydate { get; set; } 

any appreciated.

i've not set value on input. idiot.

<input type="text" class="input-small datepicker" id="@viewbag.id" name="@viewbag.id" value="@model.tostring("dd/mm/yyyy")" />