wpf - Two way binding to different value than -

is there way in wpf can getb value property display in textbox, when value of textbox updated, update different property on bound object? eg: 2 fields - quantity , newquantity. thinking along lines of imultivalueconverter if try add binding object , "two way binding requires path or xpath error".

the problem i'm using web service, proxy classes autogenerated.

i'm not sure i'd recommend it, because horrible bit of code, could in viewmodel behaviour want:

private string _quantity; private string _newquantity;  //bind public string quantity {     { return _quantity; }     set { _newquantity = value; } }  public string newquantity {     { return _newquantity; } }