我有一个类，叫它Book，它的属性叫Name。有了这个属性，我就有了一个与之关联的属性。
public class Book
{
[Author("AuthorName")]
public string Name
{
get; private set;
}
}
在我的主要方法中，我使用反射，并希望获得每个属性的每个属性的键值对。因此，在本例中，我希望看到属性名为“Author”，属性值为“AuthorName”。
问:如何使用反射获取属性上的属性名和值?
当前回答
这里有一些静态方法，可以用来获取MaxLength或任何其他属性。
using System;
using System.Linq;
using System.Reflection;
using System.ComponentModel.DataAnnotations;
using System.Linq.Expressions;
public static class AttributeHelpers {
public static Int32 GetMaxLength<T>(Expression<Func<T,string>> propertyExpression) {
return GetPropertyAttributeValue<T,string,MaxLengthAttribute,Int32>(propertyExpression,attr => attr.Length);
}
//Optional Extension method
public static Int32 GetMaxLength<T>(this T instance,Expression<Func<T,string>> propertyExpression) {
return GetMaxLength<T>(propertyExpression);
}
//Required generic method to get any property attribute from any class
public static TValue GetPropertyAttributeValue<T, TOut, TAttribute, TValue>(Expression<Func<T,TOut>> propertyExpression,Func<TAttribute,TValue> valueSelector) where TAttribute : Attribute {
var expression = (MemberExpression)propertyExpression.Body;
var propertyInfo = (PropertyInfo)expression.Member;
var attr = propertyInfo.GetCustomAttributes(typeof(TAttribute),true).FirstOrDefault() as TAttribute;
if (attr==null) {
throw new MissingMemberException(typeof(T).Name+"."+propertyInfo.Name,typeof(TAttribute).Name);
}
return valueSelector(attr);
}
}
使用静态方法…
var length = AttributeHelpers.GetMaxLength<Player>(x => x.PlayerName);
或者在实例上使用可选的扩展方法…
var player = new Player();
var length = player.GetMaxLength(x => x.PlayerName);
或者对任何其他属性使用完整的静态方法(例如StringLength)…
var length = AttributeHelpers.GetPropertyAttributeValue<Player,string,StringLengthAttribute,Int32>(prop => prop.PlayerName,attr => attr.MaximumLength);
受到Mikael Engver回答的启发。
其他回答
foreach (var p in model.GetType().GetProperties())
{
var valueOfDisplay =
p.GetCustomAttributesData()
.Any(a => a.AttributeType.Name == "DisplayNameAttribute") ?
p.GetCustomAttribute<DisplayNameAttribute>().DisplayName :
p.Name;
}
在这个例子中，我使用DisplayName而不是Author，因为它有一个名为“DisplayName”的字段要显示一个值。
如果你的意思是“对于带有一个参数的属性，列出属性名称和参数值”，那么在。net 4.5中通过CustomAttributeData API会更容易:
using System.Collections.Generic;
using System.ComponentModel;
using System.Reflection;
public static class Program
{
static void Main()
{
PropertyInfo prop = typeof(Foo).GetProperty("Bar");
var vals = GetPropertyAttributes(prop);
// has: DisplayName = "abc", Browsable = false
}
public static Dictionary<string, object> GetPropertyAttributes(PropertyInfo property)
{
Dictionary<string, object> attribs = new Dictionary<string, object>();
// look for attributes that takes one constructor argument
foreach (CustomAttributeData attribData in property.GetCustomAttributesData())
{
if(attribData.ConstructorArguments.Count == 1)
{
string typeName = attribData.Constructor.DeclaringType.Name;
if (typeName.EndsWith("Attribute")) typeName = typeName.Substring(0, typeName.Length - 9);
attribs[typeName] = attribData.ConstructorArguments[0].Value;
}
}
return attribs;
}
}
class Foo
{
[DisplayName("abc")]
[Browsable(false)]
public string Bar { get; set; }
}
我把它写进一个动态方法中，因为我在整个应用程序中使用了很多属性。方法:
public static dynamic GetAttribute(Type objectType, string propertyName, Type attrType)
{
//get the property
var property = objectType.GetProperty(propertyName);
//check for object relation
return property.GetCustomAttributes().FirstOrDefault(x => x.GetType() == attrType);
}
用法:
var objectRelAttr = GetAttribute(typeof(Person), "Country", typeof(ObjectRelationAttribute));
var displayNameAttr = GetAttribute(typeof(Product), "Category", typeof(DisplayNameAttribute));
希望这对大家有所帮助
这里有一些静态方法，可以用来获取MaxLength或任何其他属性。
using System;
using System.Linq;
using System.Reflection;
using System.ComponentModel.DataAnnotations;
using System.Linq.Expressions;
public static class AttributeHelpers {
public static Int32 GetMaxLength<T>(Expression<Func<T,string>> propertyExpression) {
return GetPropertyAttributeValue<T,string,MaxLengthAttribute,Int32>(propertyExpression,attr => attr.Length);
}
//Optional Extension method
public static Int32 GetMaxLength<T>(this T instance,Expression<Func<T,string>> propertyExpression) {
return GetMaxLength<T>(propertyExpression);
}
//Required generic method to get any property attribute from any class
public static TValue GetPropertyAttributeValue<T, TOut, TAttribute, TValue>(Expression<Func<T,TOut>> propertyExpression,Func<TAttribute,TValue> valueSelector) where TAttribute : Attribute {
var expression = (MemberExpression)propertyExpression.Body;
var propertyInfo = (PropertyInfo)expression.Member;
var attr = propertyInfo.GetCustomAttributes(typeof(TAttribute),true).FirstOrDefault() as TAttribute;
if (attr==null) {
throw new MissingMemberException(typeof(T).Name+"."+propertyInfo.Name,typeof(TAttribute).Name);
}
return valueSelector(attr);
}
}
使用静态方法…
var length = AttributeHelpers.GetMaxLength<Player>(x => x.PlayerName);
或者在实例上使用可选的扩展方法…
var player = new Player();
var length = player.GetMaxLength(x => x.PlayerName);
或者对任何其他属性使用完整的静态方法(例如StringLength)…
var length = AttributeHelpers.GetPropertyAttributeValue<Player,string,StringLengthAttribute,Int32>(prop => prop.PlayerName,attr => attr.MaximumLength);
受到Mikael Engver回答的启发。
如果你只想要一个特定的属性值，例如Display Attribute，你可以使用以下代码:
var pInfo = typeof(Book).GetProperty("Name")
.GetCustomAttribute<DisplayAttribute>();
var name = pInfo.Name;
