c# - Interface IDataErrorInfo isn't working -

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i have following class have implemented idataerrorinfo interface doesn't work i.e doesn't validation. code seems perfect. dont know why. put break point , doesn't enter idataerrorinfo members region.

product class

[datacontract()] public class product : idataerrorinfo {     [datamember()]     public string name{get;set;}     [datamember()]     public string code{get;set;}      #region idataerrorinfo members      public string error     {                 {             return null;         }     }      public string this[string property]     {                 {             switch (property)             {                 case "name":                     if (string.isnullorempty(name))                         return "name required";                     break;                 case "code":                     if (string.isnullorempty(code))                         return "code required";                     break;                 default:                     break;             }             return null;         }     }      #endregion      public product(string name, string code)     {         name = name;         code = code;     }  }

xaml binding textbox

<textbox grid.column="1"                           horizontalalignment="left"                           height="23"                           margin="24,9,0,0"                           textwrapping="wrap"                           verticalalignment="top"                           width="148" x:name="txtname"                           text="{binding name,mode=twoway,validatesondataerrors=true}"                           maxlength="50"/>

you need make object observable using inotifypropertychanged along idataerrorinfo in order the binding know properties have changed , check if there errors when validatesondataerrors=true

public class product : idataerrorinfo, inotifypropertychanged {     string _name;     [datamember()]     public string name{         { return _name; }         set {             _name = value;             notifypropertychanged("name");         }     }      //...other code removed brevity      public event propertychangedeventhandler propertychanged;      protected void notifypropertychanged(string propertyname) {         propertychangedeventhandler handler = propertychanged;         if (handler != null) {             handler(this, new propertychangedeventargs(propertyname));         }     } }

you move property changed functionality out base class reuse so

public abstract class propertychangedbase: inotifypropertychanged {      public event propertychangedeventhandler propertychanged;      protected void notifypropertychanged(string propertyname) {         propertychangedeventhandler handler = propertychanged;         if (handler != null) {             handler(this, new propertychangedeventargs(propertyname));         }     } }

and use 

public class product : propertychangedbase, idataerrorinfo {     //code removed brevity }

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