wpf controls - WPF Validation On StartDate and EndDate (StartDate less than Enddate) -

i achieving function "wpf validation on startdate , enddate (startdate less enddate)", write code in code behind throw exception if enddate less startdate, , works. met problem validation on startdate , enddate fileds. since these 2 properties compulsory fields in database, save button should disabled unless fill these 2 fields. startdate , enddate fileds not compulsory. attaching codes. can please spare few minutes @ code , provide suggestions? many thanks.

code behind

public partial class organisationtypesview : usercontrol {      organisationtypeviewmodel _datacontext = new organisationtypeviewmodel();     public organisationtypesview()     {         initializecomponent();       this.datacontext = _datacontext;          _datacontext.accountstartdate = datetime.now;         _datacontext.accountenddate = datetime.now.addmonths(1);         this.loaded += new routedeventhandler(organisationtypesview_loaded);     }      void organisationtypesview_loaded(object sender, routedeventargs e)     {      }  } 

xmal

<wpftoolkit:datepicker grid.column="1" grid.row="4" name="dpaccstart" verticalalignment="top"          selecteddate="{binding accountstartdate, mode=twoway, updatesourcetrigger=propertychanged, validatesondataerrors=true, notifyonvalidationerror=true}" />  <wpftoolkit:datepicker grid.column="1" grid.row="5" name="dpaccend" verticalalignment="top"          selecteddate="{binding accountenddate, mode=twoway, updatesourcetrigger=propertychanged, validatesondataerrors=true, notifyonvalidationerror=true}"/> 

viewmodel

    private datetime? _accountstartdate;     private datetime? _accountenddate;             public event propertychangedeventhandler propertychanged;       [required(errormessage = "account start date required field.")]     public datetime? accountstartdate     {         { return _accountstartdate; }         set         {              if (_accountstartdate != datetime.minvalue && accountenddate != datetime.minvalue)             {                  if (value > _accountenddate)                 {                                             messagebox.show("start date must less end date");                     value = this.accountstartdate;                                     }              }             _accountstartdate = value;             if (propertychanged != null)             {                 propertychanged(this, new propertychangedeventargs("accountstartdate"));             }         }     }      [required(errormessage = "account end date required field.")]     public datetime? accountenddate     {         { return _accountenddate; }         set         {             if (_accountstartdate != datetime.minvalue && accountenddate != datetime.minvalue)             {                 if (_accountstartdate > value)                 {                     messagebox.show("end date must after start date");                     value = this.accountenddate;                 }             }              _accountenddate = value;              if (propertychanged != null)             {                 propertychanged(this, new propertychangedeventargs("accountenddate"));             }       }     } 

what want validation rule based on completness of bound class. let viewmodel implement inotifydataerrorinfo interface , implement geterrors, haserrors, etc.

finally add

validatesonnotifydataerrors=true  

to binding.

this allows check consistency of entire model, not single properties.