反射 - 获取属性的属性名称和值

Question

我有一个类，让我们用名为Name的属性调用它。使用该属性，我有一个与之关联的属性。

public class Book
{
    [Author("AuthorName")]
    public string Name
    {
        get; private set; 
    }
}

在我的main方法中，我正在使用反射并希望为每个属性获取每个属性的键值对。所以在这个例子中，我希望看到属性名称为“Author”，属性值为“AuthorName”。

问题：如何使用Reflection？

获取属性的属性名称和值

Answer 1

使用typeof(Book).GetProperties()获取PropertyInfo个实例数组。然后在每个GetCustomAttributes()上使用PropertyInfo查看其中是否有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。

沿着这些行扫描类型以查找具有特定属性类型的属性并在字典中返回数据（请注意，通过将类型传递到例程中可以使其更加动态化）：

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;
}

Answer 2

要获取字典中属性的所有属性，请使用：

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

如果您想要包含继承属性，请记住将false更改为true。

Answer 3

如果您只想要一个特定的属性值对于实例显示属性，您可以使用以下代码：

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

Answer 4

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

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

Answer 5

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"

Answer 6

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; }
}

Answer 7

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

Answer 8

Necromancing。
对于那些仍然需要维护.NET 2.0的人，或那些想要在没有LINQ的情况下继续维护的人：

SELECT
  TOP 1 WITH TIES 
    *
FROM <yourtable>
ORDER BY
  row_number()over
    (partition by dateadd(hour, datediff(hour, 0, Date_time),0) ORDER BY Date_time)

使用示例：

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);
}

或只是

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

Answer 9

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：

 //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();

Answer 10

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，我使用了DisplayName而不是Author，因为它有一个名为'DisplayName'的字段，用一个值显示。

Answer 11

以下是一些静态方法，可用于获取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全静态方法（例如StringLength）...

var length = AttributeHelpers.GetPropertyAttributeValue<Player,string,StringLengthAttribute,Int32>(prop => prop.PlayerName,attr => attr.MaximumLength);

受Mikael Engver的回答启发。

Answer 12

从enum获取属性，我使用：

 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);

Answer 13

只是在寻找合适的位置放置这段代码。

假设您具有以下属性：

DEBUG [DataFeederThread] (HttpOutput.java:224) - 
org.eclipse.jetty.io.EofException: null
        at org.eclipse.jetty.server.HttpConnection$SendCallback.reset(HttpConnection.java:704) ~[jetty-server.jar:9.4.8.v20171121]
        at org.eclipse.jetty.server.HttpConnection$SendCallback.access$300(HttpConnection.java:668) ~[jetty-server.jar:9.4.8.v20171121]
        at org.eclipse.jetty.server.HttpConnection.send(HttpConnection.java:526) ~[jetty-server.jar:9.4.8.v20171121]
        at org.eclipse.jetty.server.HttpChannel.sendResponse(HttpChannel.java:778) ~[jetty-server.jar:9.4.8.v20171121]
        at org.eclipse.jetty.server.HttpChannel.write(HttpChannel.java:834) ~[jetty-server.jar:9.4.8.v20171121]
        at org.eclipse.jetty.server.HttpOutput.write(HttpOutput.java:234) [jetty-server.jar:9.4.8.v20171121]
        at org.eclipse.jetty.server.HttpOutput.write(HttpOutput.java:218) [jetty-server.jar:9.4.8.v20171121]
        at org.eclipse.jetty.server.HttpOutput.flush(HttpOutput.java:392) [jetty-server.jar:9.4.8.v20171121]
        at com.example.QueuePollServlet$QueueWriteListener.writeImpl()
        at com.example.QueuePollServlet$QueueWriteListener.dataArrived()


DEBUG [DataFeederThread] (QueuePollServlet.java:217) - messageArrived exception
org.eclipse.jetty.io.EofException: Closed
        at org.eclipse.jetty.server.HttpOutput.write(HttpOutput.java:476) ~[jetty-server.jar:9.4.8.v20171121]
        at com.example.QueuePollServlet$QueueWriteListener.writeImpl()
        at com.example.QueuePollServlet$QueueWriteListener.dataArrived()

您想获取ShortName值。您可以这样做：

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

或者更笼统地说：

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

Answer 14

虽然以上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。

如果您的类具有始终具有相同属性的多个属性，并且您希望将这些属性排序到字典中，请按以下步骤操作：

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

这仍然使用强制类型转换，但是确保强制转换将始终有效，因为您只会获得类型为“ AuthorName”的自定义属性。 如果您在上述属性中具有多个属性，则答案将强制转换。

Answer 15

由于我在整个应用程序中使用了许多属性，因此我将其写为动态方法。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