我有以下自定义属性,可以应用于属性:
[AttributeUsage(AttributeTargets.Property, AllowMultiple = false)]
public class IdentifierAttribute : Attribute
{
}
例如:
public class MyClass
{
[Identifier()]
public string Name { get; set; }
public int SomeNumber { get; set; }
public string SomeOtherProperty { get; set; }
}
还有其他类,可以将 Identifier 属性添加到不同类型的属性中:
public class MyOtherClass
{
public string Name { get; set; }
[Identifier()]
public int SomeNumber { get; set; }
public string SomeOtherProperty { get; set; }
}
然后我需要能够在我的消费类中获取这些信息。 例如:
public class TestClass<T>
{
public void GetIDForPassedInObject(T obj)
{
var type = obj.GetType();
//type.GetCustomAttributes(true)???
}
}
解决这个问题的最佳方法是什么? 我需要获取 [Identifier()] 字段的类型(int、string 等)和实际值,显然是基于类型的。
类似于下面的内容,这将仅使用它遇到的具有该属性的第一个属性,当然您可以将其放置在多个属性上..
public object GetIDForPassedInObject(T obj)
{
var prop = typeof(T).GetProperties(BindingFlags.Public | BindingFlags.Instance)
.FirstOrDefault(p => p.GetCustomAttributes(typeof(IdentifierAttribute), false).Count() ==1);
object ret = prop !=null ? prop.GetValue(obj, null) : null;
return ret;
}
public class TestClass<T>
{
public void GetIDForPassedInObject(T obj)
{
PropertyInfo[] properties =
obj.GetType().GetProperties(BindingFlags.Public | BindingFlags.Instance);
PropertyInfo IdProperty = (from PropertyInfo property in properties
where property.GetCustomAttributes(typeof(Identifier), true).Length > 0
select property).First();
if(null == IdProperty)
throw new ArgumentException("obj does not have Identifier.");
Object propValue = IdProperty.GetValue(entity, null)
}
}
有点晚了,但这是我为枚举(也可以是任何对象)所做的事情,并使用扩展获取描述属性值(这可以是任何属性的通用属性):
public enum TransactionTypeEnum
{
[Description("Text here!")]
DROP = 1,
[Description("More text here!")]
PICKUP = 2,
...
}
获取值:
var code = TransactionTypeEnum.DROP.ToCode();
支持我所有枚举的扩展:
public static string ToCode(this TransactionTypeEnum val)
{
return GetCode(val);
}
public static string ToCode(this DockStatusEnum val)
{
return GetCode(val);
}
public static string ToCode(this TrailerStatusEnum val)
{
return GetCode(val);
}
public static string ToCode(this DockTrailerStatusEnum val)
{
return GetCode(val);
}
public static string ToCode(this EncodingType val)
{
return GetCode(val);
}
private static string GetCode(object val)
{
var attributes = (DescriptionAttribute[])val.GetType().GetField(val.ToString()).GetCustomAttributes(typeof(DescriptionAttribute), false);
return attributes.Length > 0 ? attributes[0].Description : string.Empty;
}
我已经使用接受参数的属性扩展了您的示例,并且可以使用一个属性
[AttributeUsage(AttributeTargets.Property,AllowMultiple = true)]
public class PersonAttribute : Attribute
{
public readonly string FieldName;
public readonly string FieldType;
public PersonAttribute(string name,string type)
{
FieldName = name;
FieldType = type;
}
}
该属性应用于
Person
类,如下所示:
public class Person
{
public string FirstName {get;set;} = "FirstName";
public string LastName {get;set;} = "LastName";
[Person("addressline1","db")]
[Person("new_address1","system")]
public string AddressLine1 {get;set;} = "Banglore";
[Person("addressline2","system")]
public string AddressLine2 {get;set;} = "Karnataka";
[Person("addressline3","dto")]
public string AddressLine3 {get;set;} = "INDIA";
}
我创建了以下通用扩展函数,它将能够从类中读取所有属性和属性值。
public static class AttributesExt
{
public static IEnumerable<PropertyInfo> AllAttributes<T>(this object obj,string name)
{
var allProperties = obj.GetType().GetProperties()
.Where(_ => _.GetCustomAttributes(typeof(T), true).Length >= 1 && _.Name == name);
return allProperties;
}
public static IEnumerable<PropertyInfo> AllAttributes<T>(this object obj)
{
var allProperties = obj.GetType().GetProperties()
.Where(_ => _.GetCustomAttributes(typeof(T), true).Length >= 1);
return allProperties;
}
public static T ReadAttribute<T>(this PropertyInfo propertyInfo)
{
var returnType = propertyInfo.GetCustomAttributes(typeof(T), true)
.Cast<T>().FirstOrDefault();
return returnType;
}
}
现在在 main 方法中如果我们写
void Main()
{
Person p = new Person();
var all = p.AllAttributes<PersonAttribute>().Dump(); //Get All custom attributes
p.AllAttributes<PersonAttribute>("AddressLine3").Dump();
all.First(_=> _.Name == "AddressLine2").ReadAttribute<PersonAttribute>().Dump();
all.First(_=> _.Name == "AddressLine2").ReadAttribute<PersonAttribute>().FieldName.Dump();
}
我们可以按照下面的屏幕截图读取这些值。
这是一个更真实的例子。我们使用扩展方法并检查属性是否包含 FieldMetaDataAttribute (我的源代码库中的自定义属性) 具有有效的主要版本和次要版本。人们普遍感兴趣的是我们使用父类类型和 GetProperties 并检索 ProperyInfo,然后在这种特殊情况下使用 GetCustomAttribute 检索属性 FieldMetaDataAttribute 的部分。使用此代码来获取如何以更通用的方式检索自定义属性的灵感。当然可以对其进行改进,以创建一个通用方法来检索类实例的任何属性的给定属性。
/// <summary>
/// Executes the action if not the field is deprecated
/// </summary>
/// <typeparam name="TProperty"></typeparam>
/// <typeparam name="TForm"></typeparam>
/// <param name="form"></param>
/// <param name="memberExpression"></param>
/// <param name="actionToPerform"></param>
/// <returns>True if the action was performed</returns>
public static bool ExecuteActionIfNotDeprecated<TForm, TProperty>(this TForm form, Expression<Func<TForm, TProperty>> memberExpression, Action actionToPerform)
{
var memberExpressionConverted = memberExpression.Body as MemberExpression;
if (memberExpressionConverted == null)
return false;
string memberName = memberExpressionConverted.Member.Name;
PropertyInfo matchingProperty = typeof(TForm).GetProperties(BindingFlags.Public | BindingFlags.Instance)
.FirstOrDefault(p => p.Name == memberName);
if (matchingProperty == null)
return false; //should not occur
var fieldMeta = matchingProperty.GetCustomAttribute(typeof(FieldMetadataAttribute), true) as FieldMetadataAttribute;
if (fieldMeta == null)
{
actionToPerform();
return true;
}
var formConverted = form as FormDataContract;
if (formConverted == null)
return false;
if (fieldMeta.DeprecatedFromMajorVersion > 0 && formConverted.MajorVersion > fieldMeta.DeprecatedFromMajorVersion)
{
//major version of formConverted is deprecated for this field - do not execute action
return false;
}
if (fieldMeta.DeprecatedFromMinorVersion > 0 && fieldMeta.DeprecatedFromMajorVersion > 0
&& formConverted.MinorVersion >= fieldMeta.DeprecatedFromMinorVersion
&& formConverted.MajorVersion >= fieldMeta.DeprecatedFromMajorVersion)
return false; //the field is expired - do not invoke action
actionToPerform();
return true;
}