SFDataForm and binding

I have a SFDataForm declared in xaml and bound to an Item in my ViewModel. In the ViewModel when i set the value like Item.Number = "123456" (see SomeMethod) in the ViewModel, the SFDataForm doesn't update the value on the user interface. Can you please advise how I can update the field on the SFDataForm  to reflect the new value. 

public class DataFormViewModel      {          private DataFormModel _item;          public DataFormModel Item          {              get { return _item; }              set              {                  _item = value;              }          }          public void SomeMethod()          {              this.Item.Number = "123456";          }          public DataFormViewModel()          {              this._item = new DataFormModel();              this.SomeMethod();          }      }

Yes it does work on initial initialization. I modified your sample to do what I'm trying to do. I added a button. Button changes the Number to "hello World". Notice its not updated on the SfDataForm.
Attachment: DataForm_4e1390ad.zip

[XAML]      <dataForm:SfDataForm Grid.Row="1" x:Name="dataForm" DataObject="{Binding Item}" NotifyPropertyChanges="True"/>

[C#]              public DataFormModel Item      {              get { return _item; }              set              {                  _item = value;                  this.RaisePropertyChanged("Item");              }       }

Thanks so much that solved a lot of problems. Wish the property NotifyPropertyChanges="True" would of been documented below: