c# - Unable to cast object of type 'MS.Internal.NamedObject' to DoctorModel -

i have entity type called doctor have created model can use inotifypropertychange on items in entity. in model called doctormodel, have following function give me exception:

unable cast object of type 'ms.internal.namedobject' doctormodel

    // overloaded methods     public override int gethashcode()     {         return id ^ 7;     }      public override bool equals(object obj)     {         // check null           if (referenceequals(obj, null))             return false;         // check same reference           if (referenceequals(this, obj))             return true;         var model = (doctormodel)obj;   <-- exception here -->         return this.id == model.id;     } 

edit: creating observablecollection of type when try remove element, not remove it. saw article on site showed use technique when tying described. article referring @ following: http://www.c-sharpcorner.com/uploadfile/tirthacs/remove-an-item-form-observable-collection-using-remove/

just posting solution question in case else benefit it.

public override int gethashcode() {   return string.format("doctormodel{0}", this.id.tostring()).gethashcode(); }  public override bool equals(object obj) {    var newobj = obj doctormodel;     if (null != newobj)    {        return this.gethashcode() == newobj.gethashcode();    }    else    {        return base.equals(obj);    } }