反射 - 获取属性的属性名称和值

使用 typeof(Book).GetProperties() 获取 PropertyInfo 实例的数组。然后在每个 PropertyInfo 上使用 GetCustomAttributes() 以查看其中是否有任何 Author 属性类型。如果是这样，您可以从属性信息中获取属性的名称，并从属性中获取属性值。

沿着这些思路扫描具有特定属性类型的属性的类型并在字典中返回数据（请注意，这可以通过将类型传递到例程中变得更加动态）：

public static Dictionary<string, string> GetAuthors()
{
    Dictionary<string, string> _dict = new Dictionary<string, string>();

    PropertyInfo[] props = typeof(Book).GetProperties();
    foreach (PropertyInfo prop in props)
    {
        object[] attrs = prop.GetCustomAttributes(true);
        foreach (object attr in attrs)
        {
            AuthorAttribute authAttr = attr as AuthorAttribute;
            if (authAttr != null)
            {
                string propName = prop.Name;
                string auth = authAttr.Name;

                _dict.Add(propName, auth);
            }
        }
    }

    return _dict;
}

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要获取字典中属性的所有属性，请使用以下命令：

typeof(Book)
  .GetProperty("Name")
  .GetCustomAttributes(false) 
  .ToDictionary(a => a.GetType().Name, a => a);

如果您还想包含继承的属性，请记住从 false 更改为 true。

---

如果您只想要一个特定的属性值，例如显示属性，您可以使用以下代码：

var pInfo = typeof(Book).GetProperty("Name")
                             .GetCustomAttribute<DisplayAttribute>();
var name = pInfo.Name;

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我通过编写通用扩展属性属性助手解决了类似的问题：

using System;
using System.Linq;
using System.Linq.Expressions;
using System.Reflection;

public static class AttributeHelper
{
    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;
        return attr != null ? valueSelector(attr) : default(TValue);
    }
}

用法：

var author = AttributeHelper.GetPropertyAttributeValue<Book, string, AuthorAttribute, string>(prop => prop.Name, attr => attr.Author);
// author = "AuthorName"

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您可以使用 GetCustomAttributesData() 和 GetCustomAttributes()：

var attributeData = typeof(Book).GetProperty("Name").GetCustomAttributesData();
var attributes = typeof(Book).GetProperty("Name").GetCustomAttributes(false);

---

如果您的意思是“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; }
}

---

private static Dictionary<string, string> GetAuthors()
{
    return typeof(Book).GetProperties()
        .SelectMany(prop => prop.GetCustomAttributes())
        .OfType<AuthorAttribute>()
        .ToDictionary(a => a.GetType().Name.Replace("Attribute", ""), a => a.Name);
}

使用泛型的示例（目标框架 4.5）

using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;

private static Dictionary<string, string> GetAttribute<TAttribute, TType>(
    Func<TAttribute, string> valueFunc)
    where TAttribute : Attribute
{
    return typeof(TType).GetProperties()
        .SelectMany(p => p.GetCustomAttributes())
        .OfType<TAttribute>()
        .ToDictionary(a => a.GetType().Name.Replace("Attribute", ""), valueFunc);
}

用法

var dictionary = GetAttribute<AuthorAttribute, Book>(a => a.Name);

---

public static class PropertyInfoExtensions
{
    public static TValue GetAttributValue<TAttribute, TValue>(this PropertyInfo prop, Func<TAttribute, TValue> value) where TAttribute : Attribute
    {
        var att = prop.GetCustomAttributes(
            typeof(TAttribute), true
            ).FirstOrDefault() as TAttribute;
        if (att != null)
        {
            return value(att);
        }
        return default(TValue);
    }
}

用法：

 //get class properties with attribute [AuthorAttribute]
        var props = typeof(Book).GetProperties().Where(prop => Attribute.IsDefined(prop, typeof(AuthorAttribute)));
            foreach (var prop in props)
            {
               string value = prop.GetAttributValue((AuthorAttribute a) => a.Name);
            }

或者：

 //get class properties with attribute [AuthorAttribute]
        var props = typeof(Book).GetProperties().Where(prop => Attribute.IsDefined(prop, typeof(AuthorAttribute)));
        IList<string> values = props.Select(prop => prop.GetAttributValue((AuthorAttribute a) => a.Name)).Where(attr => attr != null).ToList();

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以下是一些可用于获取 MaxLength 或任何其他属性的静态方法。

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 的回答的启发。

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虽然上述最受好评的答案肯定有效，但我建议在某些情况下使用稍微不同的方法。

如果您的类有多个属性始终具有相同的属性，并且您希望将这些属性排序到字典中，则方法如下：

var dict = typeof(Book).GetProperties().ToDictionary(p => p.Name, p => p.GetCustomAttributes(typeof(AuthorName), false).Select(a => (AuthorName)a).FirstOrDefault());

这仍然使用强制转换，但确保强制转换始终有效，因为您只会获得“AuthorName”类型的自定义属性。如果您有多个以上答案的属性，则会出现强制转换异常。

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我把它写成一个动态方法，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));

希望这对任何人都有帮助

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死灵术。对于那些仍然需要维护 .NET 2.0 的人，或者那些想要不使用 LINQ 的人：

public static object GetAttribute(System.Reflection.MemberInfo mi, System.Type t)
{
    object[] objs = mi.GetCustomAttributes(t, true);

    if (objs == null || objs.Length < 1)
        return null;

    return objs[0];
}



public static T GetAttribute<T>(System.Reflection.MemberInfo mi)
{
    return (T)GetAttribute(mi, typeof(T));
}


public delegate TResult GetValue_t<in T, out TResult>(T arg1);

public static TValue GetAttributValue<TAttribute, TValue>(System.Reflection.MemberInfo mi, GetValue_t<TAttribute, TValue> value) where TAttribute : System.Attribute
{
    TAttribute[] objAtts = (TAttribute[])mi.GetCustomAttributes(typeof(TAttribute), true);
    TAttribute att = (objAtts == null || objAtts.Length < 1) ? default(TAttribute) : objAtts[0];
    // TAttribute att = (TAttribute)GetAttribute(mi, typeof(TAttribute));

    if (att != null)
    {
        return value(att);
    }
    return default(TValue);
}

示例用法：

System.Reflection.FieldInfo fi = t.GetField("PrintBackground");
wkHtmlOptionNameAttribute att = GetAttribute<wkHtmlOptionNameAttribute>(fi);
string name = GetAttributValue<wkHtmlOptionNameAttribute, string>(fi, delegate(wkHtmlOptionNameAttribute a){ return a.Name;});

或者干脆

string aname = GetAttributValue<wkHtmlOptionNameAttribute, string>(fi, a => a.Name );

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只是在寻找放置这段代码的正确位置。

假设您具有以下属性：

[Display(Name = "Solar Radiation (Average)", ShortName = "SolarRadiationAvg")]
public int SolarRadiationAvgSensorId { get; set; }

并且您想要获取 ShortName 值。你可以做：

((DisplayAttribute)(typeof(SensorsModel).GetProperty(SolarRadiationAvgSensorId).GetCustomAttribute(typeof(DisplayAttribute)))).ShortName;

或使其通用：

internal static string GetPropertyAttributeShortName(string propertyName)
{
    return ((DisplayAttribute)(typeof(SensorsModel).GetProperty(propertyName).GetCustomAttribute(typeof(DisplayAttribute)))).ShortName;
}

---

foreach (var p in model.GetType().GetProperties())
{
   var valueOfDisplay = 
       p.GetCustomAttributesData()
        .Any(a => a.AttributeType.Name == "DisplayNameAttribute") ? 
            p.GetCustomAttribute<DisplayNameAttribute>().DisplayName : 
            p.Name;
}

在此示例中，我使用了 DisplayName 而不是 Author，因为它有一个名为“DisplayName”的字段要显示一个值。

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要从枚举中获取属性，我正在使用：

 public enum ExceptionCodes
 {
  [ExceptionCode(1000)]
  InternalError,
 }

 public static (int code, string message) Translate(ExceptionCodes code)
        {
            return code.GetType()
            .GetField(Enum.GetName(typeof(ExceptionCodes), code))
            .GetCustomAttributes(false).Where((attr) =>
            {
                return (attr is ExceptionCodeAttribute);
            }).Select(customAttr =>
            {
                var attr = (customAttr as ExceptionCodeAttribute);
                return (attr.Code, attr.FriendlyMessage);
            }).FirstOrDefault();
        }

// 使用

 var _message = Translate(code);

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如果您想获取具有自定义属性的属性，请尝试以下操作：

IEnumerable propertyInfos = properties.GetType().GetProperties();

PropertyInfo p = propertyInfos.Where(x => x.GetCustomAttribute() != null);

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