c# - ItemSource in DataGrid Error: Exception has been thrown by the target of an invocation -

when call headersdatagrid.itemssource application throws exception. can please me debug , determine error is? thanks

code

public static list<item> getheaders()     {         item i1 = new item();         i1.label = "tst";         i1.description = "this header testing";         item i2 = new item();         i2.label = "ts2";         i2.description = "this second header , used testing purposes :)";         item i3 = new item();         i3.label = "ts3";         i3.description = "this third header , used testing purposes :d";         list<item> headers = new list<item>();         headers.add(i1);         headers.add(i2);         headers.add(i3);         return headers;     }        public mainwindow()     {         displayheaders();         initializecomponent();     }      /// <summary>     /// purpose of method display of headers     /// </summary>     public void displayheaders()     {         //list<item> headers = database.getheaders();          // testing purposes         list<item> headers = testingclass.getheaders();          // handle headers         headersdatagrid.itemssource = headers;               } 

xml

            <grid name="grid_headers" background="honeydew">                 <datagrid x:name="headersdatagrid" autogeneratecolumns="true"></datagrid>             </grid> 

the error indicates headersdatagrid null. try moving displayheaders method post initialize component call.