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
{}
我想产生的是:
//This should return "MyTable"
String DomainNameValue = GetDomainName<MyClass>();
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
{}
我想产生的是:
//This should return "MyTable"
String DomainNameValue = GetDomainName<MyClass>();
Answers:
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:
可以进一步推广此方法以使用任何属性:
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);
}
}
并像这样使用:
string name = typeof(MyClass)
.GetAttributeValue((DomainNameAttribute dna) => dna.Name);
const Filed
静态类?
已经存在执行此操作的扩展。
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 : "";
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);
}
}
我使用Darin Dimitrov的答案来创建泛型扩展,以获取类中任何成员的成员属性(而不是类的属性)。我将其发布在这里是因为其他人可能会发现它有用:
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);
}
}
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);
如果您在http://msdn.microsoft.com/zh-cn/library/aa288454(VS.71).aspx之前没有看过它,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/zh-cn/library/aa288454(VS.71).aspx#vcwlkattributestutorialanchor3
' 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
内联泛型函数的主体可能就很容易使用。对我来说,使函数在MyClass类型上通用没有任何意义。
string DomainName = GetAttribute<DomainNameAttribute>(typeof(MyClass)).Name
// null reference exception if MyClass doesn't have the attribute.
如果有人需要可为空的结果,并且该结果可在Enums,PropertyInfo和类中使用,则这是我解决的方法。这是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;
}
}
用法示例:
// 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();
}
而是编写大量代码,只需执行以下操作:
{
dynamic tableNameAttribute = typeof(T).CustomAttributes.FirstOrDefault().ToString();
dynamic tableName = tableNameAttribute.Substring(tableNameAttribute.LastIndexOf('.'), tableNameAttribute.LastIndexOf('\\'));
}
当您具有同名的重写方法时,请使用下面的帮助器
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);