Question

我正在尝试创建一个泛型方法，该方法将读取类的属性并在运行时返回该值。我该怎么做？

注意：DomainName属性属于DomainNameAttribute类。

[DomainName("MyTable")]
Public class MyClass : DomainBase
{}

我想要生成的内容：

//This should return "MyTable"
String DomainNameValue = GetDomainName<MyClass>();

Answer 1

public string GetDomainName<T>()
{
    var dnAttribute = typeof(T).GetCustomAttributes(
        typeof(DomainNameAttribute), true
    ).FirstOrDefault() as DomainNameAttribute;
    if (dnAttribute != null)
    {
        return dnAttribute.Name;
    }
    return null;
}

更新：

此方法可以进一步推广使用任何属性：

public static class AttributeExtensions
{
    public static TValue GetAttributeValue<TAttribute, TValue>(
        this Type type, 
        Func<TAttribute, TValue> valueSelector) 
        where TAttribute : Attribute
    {
        var att = type.GetCustomAttributes(
            typeof(TAttribute), true
        ).FirstOrDefault() as TAttribute;
        if (att != null)
        {
            return valueSelector(att);
        }
        return default(TValue);
    }
}

并使用如下：

string name = typeof(MyClass)
    .GetAttributeValue((DomainNameAttribute dna) => dna.Name);

Answer 2

已经有了扩展功能。

namespace System.Reflection
{
    // Summary:
    //     Contains static methods for retrieving custom attributes.
    public static class CustomAttributeExtensions
    {
        public static T GetCustomAttribute<T>(this MemberInfo element, bool inherit) where T : Attribute;
    }
}

所以：

var attr = typeof(MyClass).GetCustomAttribute<DomainNameAttribute>(false);
return attr != null ? attr.DomainName : "";

Answer 3

System.Reflection.MemberInfo info = typeof(MyClass);
object[] attributes = info.GetCustomAttributes(true);

for (int i = 0; i < attributes.Length; i++)
{
    if (attributes[i] is DomainNameAttribute)
    {
        System.Console.WriteLine(((DomainNameAttribute) attributes[i]).Name);
    }   
}

Answer 4

我使用Darin Dimitrov的答案来创建一个通用扩展来获取类中任何成员的成员属性（而不是类的属性）。我在这里发布它是因为其他人可能觉得它很有用：

public static class AttributeExtensions
{
    /// <summary>
    /// Returns the value of a member attribute for any member in a class.
    ///     (a member is a Field, Property, Method, etc...)    
    /// <remarks>
    /// If there is more than one member of the same name in the class, it will return the first one (this applies to overloaded methods)
    /// </remarks>
    /// <example>
    /// Read System.ComponentModel Description Attribute from method 'MyMethodName' in class 'MyClass': 
    ///     var Attribute = typeof(MyClass).GetAttribute("MyMethodName", (DescriptionAttribute d) => d.Description);
    /// </example>
    /// <param name="type">The class that contains the member as a type</param>
    /// <param name="MemberName">Name of the member in the class</param>
    /// <param name="valueSelector">Attribute type and property to get (will return first instance if there are multiple attributes of the same type)</param>
    /// <param name="inherit">true to search this member's inheritance chain to find the attributes; otherwise, false. This parameter is ignored for properties and events</param>
    /// </summary>    
    public static TValue GetAttribute<TAttribute, TValue>(this Type type, string MemberName, Func<TAttribute, TValue> valueSelector, bool inherit = false) where TAttribute : Attribute
    {
        var att = type.GetMember(MemberName).FirstOrDefault().GetCustomAttributes(typeof(TAttribute), inherit).FirstOrDefault() as TAttribute;
        if (att != null)
        {
            return valueSelector(att);
        }
        return default(TValue);
    }
}

用法示例：

//Read System.ComponentModel Description Attribute from method 'MyMethodName' in class 'MyClass'
var Attribute = typeof(MyClass).GetAttribute("MyMethodName", (DescriptionAttribute d) => d.Description);

Answer 5

如果您在http://msdn.microsoft.com/en-us/library/aa288454(VS.71).aspx

之前没有看过，那么这是一个很好的教程

您特别感兴趣的是此处的部分，称为访问属性 http://msdn.microsoft.com/en-us/library/aa288454(VS.71).aspx#vcwlkattributestutorialanchor3

Answer 6

Darin Dimitrov的第一个解决方案的简化版本：

public string GetDomainName<T>()
{
    var dnAttribute = typeof(T).GetCustomAttribute<DomainNameAttribute>(true);
    if (dnAttribute != null)
    {
        return dnAttribute.Name;
    }
    return null;
}

Answer 7

' Simplified Generic version. 
Shared Function GetAttribute(Of TAttribute)(info As MemberInfo) As TAttribute
    Return info.GetCustomAttributes(GetType(TAttribute), _
                                    False).FirstOrDefault()
End Function

' Example usage over PropertyInfo
Dim fieldAttr = GetAttribute(Of DataObjectFieldAttribute)(pInfo)
If fieldAttr IsNot Nothing AndAlso fieldAttr.PrimaryKey Then
    keys.Add(pInfo.Name)
End If

可能就像使用内联泛型函数一样容易。在MyClass类型上使函数通用是没有任何意义的。

string DomainName = GetAttribute<DomainNameAttribute>(typeof(MyClass)).Name
// null reference exception if MyClass doesn't have the attribute.

Answer 8

万一任何人需要一个可为空的结果，并且要使其在Enums，PropertyInfo和类中均有效，这就是我解决的方法。这是对Darin Dimitrov的更新解决方案的修改。

\317\200

用法示例：

public static object GetAttributeValue<TAttribute, TValue>(this object val, Func<TAttribute, TValue> valueSelector) where TAttribute : Attribute
{
    try
    {
        Type t = val.GetType();
        TAttribute attr;
        if (t.IsEnum && t.GetField(val.ToString()).GetCustomAttributes(typeof(TAttribute), true).FirstOrDefault() is TAttribute att)
        {
            // Applies to Enum values
            attr = att;
        }
        else if (val is PropertyInfo pi && pi.GetCustomAttributes(typeof(TAttribute), true).FirstOrDefault() is TAttribute piAtt)
        {
            // Applies to Properties in a Class
            attr = piAtt;
        }
        else
        {
            // Applies to classes
            attr = (TAttribute)t.GetCustomAttributes(typeof(TAttribute), false).FirstOrDefault();
        }
        return valueSelector(attr);
    }
    catch
    {
        return null;
    }
}

Answer 9

然后编写大量代码，只需执行以下操作：

{         
   dynamic tableNameAttribute = typeof(T).CustomAttributes.FirstOrDefault().ToString();
   dynamic tableName = tableNameAttribute.Substring(tableNameAttribute.LastIndexOf('.'), tableNameAttribute.LastIndexOf('\\'));    
}

如何在运行时读取类的属性？

9 个答案: