c# - 如何在运行时读取类的属性？

Question

我正在尝试创建一个通用方法，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
{}

我要生成的内容：

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

score 266 · Accepted Answer

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：

该方法可以进一步推广到任何属性：

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);
    }
}

并像这样使用：

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

score 61 · Accepted Answer

已经有一个扩展来做到这一点。

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 : "";

score 16 · Accepted Answer

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);
    }   
}

score 6 · Accepted Answer

我使用 Darin Dimitrov 的答案创建了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会觉得它有用：

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);
    }
}

使用示例：

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

score 3 · Accepted Answer

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;
}

score 0 · Accepted Answer

' 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

可能就像使用内联的通用函数体一样容易。在 MyClass 类型上使函数泛型对我来说没有任何意义。

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

score 0 · Accepted Answer

如果有人需要一个可为空的结果，并且它可以跨枚举、PropertyInfo 和类工作，这就是我解决它的方法。这是对 Darin Dimitrov 的更新解决方案的修改。

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;
    }
}

使用示例：

// Class
SettingsEnum.SettingGroup settingGroup = (SettingsEnum.SettingGroup)(this.GetAttributeValue((SettingGroupAttribute attr) => attr.Value) as SettingsEnum.SettingGroup?);

// Enum
DescriptionAttribute desc = settingGroup.GetAttributeValue((DescriptionAttribute attr) => attr) as DescriptionAttribute;

// PropertyInfo       
foreach (PropertyInfo pi in this.GetType().GetProperties())
{
    string setting = ((SettingsEnum.SettingName)(pi.GetAttributeValue((SettingNameAttribute attr) => attr.Value) as SettingsEnum.SettingName?)).ToString();
}

score 0 · Accepted Answer

当您具有相同名称的覆盖方法时使用下面的帮助器

public static TValue GetControllerMethodAttributeValue<T, TT, TAttribute, TValue>(this T type, Expression<Func<T, TT>> exp, Func<TAttribute, TValue> valueSelector) where TAttribute : Attribute
        {
            var memberExpression = exp?.Body as MethodCallExpression;

            if (memberExpression.Method.GetCustomAttributes(typeof(TAttribute), false).FirstOrDefault() is TAttribute attr && valueSelector != null)
            {
                return valueSelector(attr);
            }

            return default(TValue);
        }

用法： var someController = new SomeController(Some params); var str = typeof(SomeController).GetControllerMethodAttributeValue(x => someController.SomeMethod(It.IsAny()), (RouteAttribute routeAttribute) => routeAttribute.Template);

score -1 · Accepted Answer

与其编写大量代码，不如这样做：

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

c# - 如何在运行时读取类的属性？

9 回答 9

Related

Reference