c# - Problems setting up databinding with WPF and MVVM -

i have application uses mvvm. i'm trying set databinding combobox connecting properties in viewmodel. when run application error message:

message='provide value on 'system.windows.data.binding' threw exception.' line number '11' , line position '176'. 

the problem occurs line of xaml:

<combobox x:name="schoolcombobox" horizontalalignment="left" margin="25,80,0,0" verticalalignment="top" width="250" fontsize="16" itemssource="{binding locationlist}" selecteditem="{binding source=locationpicked}" /> 

below viewmodel i'm trying use.

using qmac.models; using system; using system.collections.generic; using system.linq; using system.text;  using system.windows;  namespace qmac.viewmodels {   class mainviewmodel : viewmodelbase   {     address address;     location location;     private string _locationpicked;      public mainviewmodel()     {         address = new address();         location = new location();     }      public list<string> locationlist     {         { return location.site; }         set         {             onpropertychanged("locationlist");         }     }      public string locationpicked     {         { return _locationpicked; }         set         {             _locationpicked = value;             messagebox.show(_locationpicked);             onpropertychanged("locationpicked");         }     }   } } 

am setting property incorrectly work databinding?

you not binding selecteditem correctly. need set path on binding , not source. i'm assuming have set datacontext mainviewmodel. since locationpicked property in mainviewmodel don't need set binding.source. change binding set path on selecteditem using {binding locationpicked.