public string this[string columnName]
        {
            get
            {
                if (!IsValidateEnabled)
                {
                    return(string.Empty);                   //未启用验证时不进行验证 add by ljc 2015-08-01
                }
                if (ValidateHelper.GetValidator(this, _type) != null)
                {
                    //先判断有没有FluentValidation错误,有的话直接返回FluentValidation错误(没有的话还按原先的方式验证)add by ljc 2015-07-29
                    var flentValidationErrors = ValidateHelper.GetFluentValidationErrors(this, columnName);
                    if (!string.IsNullOrEmpty(flentValidationErrors))
                    {
                        return(flentValidationErrors);
                    }
                    return(string.Empty);//如果用了FluentValidation,就不再用老的方式验证了 add by ljc 2015-08-03
                }

                //当ViewModel中值发生变化是触发规则验证
                var vc = new ValidationContext(this, null, null)
                {
                    MemberName = columnName
                };
                if (_propertyGetters.ContainsKey(columnName))
                {
                    //不想验证的属性就不进行验证
                    if (ExcludedValidatePropertyNames != null && ExcludedValidatePropertyNames.Contains(columnName))
                    {
                        return(string.Empty);
                    }
                    //获取触发的属性值
                    object value = _propertyGetters[columnName].GetValue(this, null);
                    //在_validators中找到相应的规则,并触发验证,返回错误信息
                    var errors = from v in _validators[columnName]
                                 select v.GetValidationResult(value, vc)
                                 into result
                                     where result != null
                                 select result.ErrorMessage;

                    //更新Error属性
                    //OnPropertyChanged("Error");//这句不能加,否则会与Error属性的Get方法形成死循环
                    return(string.Join(Environment.NewLine, errors));
                }
                //OnPropertyChanged("Error");//这句不能加,否则会与Error属性的Get方法形成死循环
                return(string.Empty);
            }
        }