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[英]Custom Validation Attribute: Comparing one property to another property's inner property
[英]Custom validation attribute that compares the value of my property with another property's value in my model class
我想創建一個自定義驗證屬性,我想在其中將my屬性的值與我的模型類中的另一個屬性值進行比較。 例如我在我的模型類中:
...
public string SourceCity { get; set; }
public string DestinationCity { get; set; }
我想創建一個自定義屬性來像這樣使用它:
[Custom("SourceCity", ErrorMessage = "the source and destination should not be equal")]
public string DestinationCity { get; set; }
//this wil lcompare SourceCity with DestinationCity
我要怎么去那兒?
以下是獲取其他屬性值的方法:
public class CustomAttribute : ValidationAttribute
{
private readonly string _other;
public CustomAttribute(string other)
{
_other = other;
}
protected override ValidationResult IsValid(object value, ValidationContext validationContext)
{
var property = validationContext.ObjectType.GetProperty(_other);
if (property == null)
{
return new ValidationResult(
string.Format("Unknown property: {0}", _other)
);
}
var otherValue = property.GetValue(validationContext.ObjectInstance, null);
// at this stage you have "value" and "otherValue" pointing
// to the value of the property on which this attribute
// is applied and the value of the other property respectively
// => you could do some checks
if (!object.Equals(value, otherValue))
{
// here we are verifying whether the 2 values are equal
// but you could do any custom validation you like
return new ValidationResult(this.FormatErrorMessage(validationContext.DisplayName));
}
return null;
}
}
請看下面我的例子:
Model類實現了INotifyPropertyChanged
public class ModelClass : INotifyPropertyChanged
{
private string destinationCity;
public string SourceCity { get; set; }
public ModelClass()
{
PropertyChanged += CustomAttribute.ThrowIfNotEquals;
}
[Custom("SourceCity", ErrorMessage = "the source and destination should not be equal")]
public string DestinationCity
{
get
{
return this.destinationCity;
}
set
{
if (value != this.destinationCity)
{
this.destinationCity = value;
NotifyPropertyChanged("DestinationCity");
}
}
}
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void NotifyPropertyChanged(string info)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(info));
}
}
}
屬性類還包含事件hendler。
internal sealed class CustomAttribute : Attribute
{
public CustomAttribute(string propertyName)
{
PropertyName = propertyName;
}
public string PropertyName { get; set; }
public string ErrorMessage { get; set; }
public static void ThrowIfNotEquals(object obj, PropertyChangedEventArgs eventArgs)
{
Type type = obj.GetType();
var changedProperty = type.GetProperty(eventArgs.PropertyName);
var attribute = (CustomAttribute)changedProperty
.GetCustomAttributes(typeof(CustomAttribute), false)
.FirstOrDefault();
var valueToCompare = type.GetProperty(attribute.PropertyName).GetValue(obj, null);
if (!valueToCompare.Equals(changedProperty.GetValue(obj, null)))
throw new Exception("the source and destination should not be equal");
}
}
用法
var test = new ModelClass();
test.SourceCity = "1";
// Everything is ok
test.DestinationCity = "1";
// throws exception
test.DestinationCity ="2";
為了簡化代碼,我決定省略驗證。
執行此操作的最佳方法是使用IValidatableObject。 請參閱http://msdn.microsoft.com/en-us/data/gg193959.aspx
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