public class User
{[Required][StringLength(20)]public string Name { get; set; }[Range(1,120)]public int Age { get; set; }
}

Validator.TryValidateObject(obj,new ValidationContext(obj),results,true);

static void Main(string[] args)
{ICollection<ValidationResult> results = null;User invalidUser = new User{Name = "My name is System.ComponentModel.DataAnnotations",Age = -1,};if(!Validate(invalidUser, out results)){Console.WriteLine(string.Join("\n", results.Select(o=>o.ErrorMessage)));}else{Console.WriteLine("I am a valid object.");}Console.ReadKey();
}static bool Validate<T>(T obj, out ICollection<ValidationResult> results)
{results = new List<ValidationResult>();return Validator.TryValidateObject(obj, new ValidationContext(obj), results, true);
}

public class User
{[Required][StringLength(20, ErrorMessage ="Out of range~")]public string Name { get; set; }[Range(1,120, ErrorMessage ="Not a valid age.")]public int Age { get; set; }
}

User validUser = new User
{Name = "Hellen",Age = 18,
};

class PropertyValidateModel : IDataErrorInfo
{public string this[string columnName]{get{List<ValidationResult> validationResults = new List<ValidationResult>();bool result = Validator.TryValidateProperty(GetType().GetProperty(columnName).GetValue(this),new ValidationContext(this){MemberName = columnName},validationResults);if (result)return null;return validationResults.First().ErrorMessage;}}public string Error{get{return null;}}
}

class User : PropertyValidateModel, INotifyPropertyChanged
{private string _name = string.Empty;private int _age = 0;[Required][StringLength(20)]public string Name{get{return _name;}set{if(_name != value){_name = value;RaisePropertyChanged("Name");}}}[Required][Range(1,120)]public int Age{get{return _age;}set{if(_age != value){_age = value;RaisePropertyChanged("Age");}}}public event PropertyChangedEventHandler PropertyChanged;protected virtual void RaisePropertyChanged(string propertyName){PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));}
}

<StackPanel><TextBlock Text="Name: "/><TextBox Text="{Binding User.Name,UpdateSourceTrigger=PropertyChanged, NotifyOnValidationError=True, ValidatesOnDataErrors=True}" Margin="0,10"><Validation.ErrorTemplate><ControlTemplate><StackPanel><AdornedElementPlaceholder x:Name="textBox" /><TextBlock Text="{Binding [0].ErrorContent}" Foreground="Red"/></StackPanel></ControlTemplate></Validation.ErrorTemplate></TextBox><TextBlock Text="Age" /><TextBox Text="{Binding User.Age, UpdateSourceTrigger=LostFocus, NotifyOnValidationError=True, ValidatesOnDataErrors=True}" Margin="0,10"><Validation.ErrorTemplate><ControlTemplate><StackPanel><AdornedElementPlaceholder x:Name="textBox" /><TextBlock Text="{Binding [0].ErrorContent}" Foreground="Red"/></StackPanel></ControlTemplate></Validation.ErrorTemplate></TextBox>
</StackPanel>

    public class DivisibleBy7Attribute : ValidationAttribute{public DivisibleBy7Attribute():base("{0} value is not divisible by 7"){}protected override ValidationResult IsValid(object value, ValidationContext validationContext){decimal val = (decimal)value;bool vaild = val % 7 == 0;if (vaild)return null;return new ValidationResult(base.FormatErrorMessage(validationContext.MemberName));}}