ICustomAttributeProvider.GetCustomAttributes Method

Fully descibed ICustomAttributeProvider Extensions

using System;
using System.Reflection;
namespace Extensions
{
public static class Reflection
{
#region ICustomAttributeProvider
/// <summary>
/// Returns the first custom attributes defined on this member, identified by type T, or null if there are no custom attributes of that type.
/// </summary>
/// <typeparam name="T">Type of the custom attributes to extract.</typeparam>
/// <param name="customAttributeProvider">Provider to extract the custom attribute from.</param>
/// <param name="inherit">When true, look up the hierarchy chain for the inherited custom attribute.</param>
/// <returns>An single custom attributes located on index zero in the custom attribute array, or null.</returns>
/// <remarks>Developered by Paw Jershauge for rapid Custom Attribute extraction.</remarks>
public static T GetCustomAttribute<T>(this ICustomAttributeProvider customAttributeProvider, bool inherit) where T : Attribute
{
T outval = null;
if (TryGetCustomAttribute<T>(customAttributeProvider, inherit, out outval))
return outval;
return null;
}
/// <summary>
/// Returns the first custom attributes defined on this member, identified by type T, or null if there are no custom attributes of that type.
/// </summary>
/// <typeparam name="T">Type of the custom attributes to extract.</typeparam>
/// <param name="customAttributeProvider">Provider to extract the custom attribute from.</param>
/// <returns>An single custom attributes located on index zero in the custom attribute array, or null.</returns>
/// <remarks>Developered by Paw Jershauge for rapid Custom Attribute extraction.</remarks>
public static T GetCustomAttribute<T>(this ICustomAttributeProvider customAttributeProvider) where T : Attribute
{
T outval = null;
if (TryGetCustomAttribute<T>(customAttributeProvider, true, out outval))
return outval;
return null;
}
/// <summary>
/// Returns an array of custom attributes defined on this member, identified by type T, or an empty array if there are no custom attributes of that type.
/// </summary>
/// <typeparam name="T">Type of the custom attributes to extract.</typeparam>
/// <param name="customAttributeProvider">Provider to extract the custom attribute from.</param>
/// <param name="inherit">When true, look up the hierarchy chain for the inherited custom attribute.</param>
/// <returns>An array of custom attributes, or an empty custom attribute array.</returns>
/// <remarks>Developered by Paw Jershauge for rapid Custom Attribute extraction.</remarks>
public static T[] GetCustomAttributes<T>(this ICustomAttributeProvider customAttributeProvider, bool inherit) where T : Attribute
{
T[] outval = null;
if (TryGetCustomAttributes<T>(customAttributeProvider, inherit, out outval))
return outval;
return new T[0];
}
/// <summary>
/// Returns an array of custom attributes defined on this member, identified by type T, or an empty array if there are no custom attributes of that type.
/// </summary>
/// <typeparam name="T">Type of the custom attributes to extract.</typeparam>
/// <param name="customAttributeProvider">Provider to extract the custom attribute from.</param>
/// <returns>An array of custom attributes, or an empty custom attribute array.</returns>
/// <remarks>Developered by Paw Jershauge for rapid Custom Attribute extraction.</remarks>
public static T[] GetCustomAttributes<T>(this ICustomAttributeProvider customAttributeProvider) where T : Attribute
{
T[] outval = null;
if (TryGetCustomAttributes<T>(customAttributeProvider, true, out outval))
return outval;
return new T[0];
}
/// <summary>
/// Extracts the first custom attributes defined on this member, identified by type T, or null if there are no custom attributes of that type.
/// A return value indicates whether the extraction was successfull or failed.
/// </summary>
/// <typeparam name="T">Type of the custom attributes to extract.</typeparam>
/// <param name="customAttributeProvider">Provider to extract the custom attribute from.</param>
/// <param name="inherit">When true, look up the hierarchy chain for the inherited custom attribute.</param>
/// <param name="value">When this method returns, contains the custom attribute value contained in customAttributeProvider, if the extraction succeeded, or null if the extraction failed. 
/// The extraction fails if the customAttributeProvider parameter is null, or customAttributeProvider does not contain the custom attribute.</param>
/// <returns>true if the extraction was successfully; otherwise, false.</returns>
/// <remarks>Developered by Paw Jershauge for rapid Custom Attribute extraction.</remarks>
public static bool TryGetCustomAttribute<T>(this ICustomAttributeProvider customAttributeProvider, bool inherit, out T value) where T : Attribute
{
value = null;
if (customAttributeProvider == null)
return false;
object[] attributes = customAttributeProvider.GetCustomAttributes(typeof(T), inherit);
if (attributes == null)
return false;
if (attributes.Length == 0)
return false;
value = (T)attributes[0];
return true;
}
/// <summary>
/// Extracts the first custom attributes defined on this member, identified by type T, or null if there are no custom attributes of that type.
/// A return value indicates whether the extraction was successfull or failed.
/// </summary>
/// <typeparam name="T">Type of the custom attributes to extract.</typeparam>
/// <param name="customAttributeProvider">Provider to extract the custom attribute from.</param>
/// <param name="value">When this method returns, contains the custom attribute value contained in customAttributeProvider, if the extraction succeeded, or null if the extraction failed. 
/// The extraction fails if the customAttributeProvider parameter is null, or customAttributeProvider does not contain the custom attribute.</param>
/// <returns>true if the extraction was successfully; otherwise, false.</returns>
/// <remarks>Developered by Paw Jershauge for rapid Custom Attribute extraction.</remarks>
public static bool TryGetCustomAttribute<T>(this ICustomAttributeProvider customAttributeProvider, out T value) where T : Attribute
{
return TryGetCustomAttribute<T>(customAttributeProvider, true, out value);
}
/// <summary>
/// Extracts an array of custom attributes defined on this member, identified by type T, or an empty array if there are no custom attributes of that type.
/// A return value indicates whether the extraction was successfull or failed.
/// </summary>
/// <typeparam name="T">Type of the custom attributes to extract.</typeparam>
/// <param name="customAttributeProvider">Provider to extract the custom attribute from.</param>
/// <param name="inherit">When true, look up the hierarchy chain for the inherited custom attribute.</param>
/// <param name="value">When this method returns, contains the custom attribute array contained in customAttributeProvider, if the extraction succeeded, or null if the extraction failed. 
/// The extraction fails if the customAttributeProvider parameter is null, or customAttributeProvider does not contain the custom attribute.</param>
/// <returns>true if the extraction was successfully; otherwise, false.</returns>
/// <remarks>Developered by Paw Jershauge for rapid Custom Attribute extraction.</remarks>
public static bool TryGetCustomAttributes<T>(this ICustomAttributeProvider customAttributeProvider, bool inherit, out T[] value) where T : Attribute
{
value = new T[0];
if (customAttributeProvider == null)
return false;
object[] attributes = customAttributeProvider.GetCustomAttributes(typeof(T), inherit);
if (attributes == null)
return false;
if (attributes.Length == 0)
return false;
value = new T[attributes.Length];
for (int i = 0; i < attributes.Length; i++)
value[i] = attributes[0] as T;
return true;
}
/// <summary>
/// Extracts an array of custom attributes defined on this member, identified by type T, or an empty array if there are no custom attributes of that type.
/// A return value indicates whether the extraction was successfull or failed.
/// </summary>
/// <typeparam name="T">Type of the custom attributes to extract.</typeparam>
/// <param name="customAttributeProvider">Provider to extract the custom attribute from.</param>
/// <param name="value">When this method returns, contains the custom attribute array contained in customAttributeProvider, if the extraction succeeded, or null if the extraction failed. 
/// The extraction fails if the customAttributeProvider parameter is null, or customAttributeProvider does not contain the custom attribute.</param>
/// <returns>true if the extraction was successfully; otherwise, false.</returns>
/// <remarks>Developered by Paw Jershauge for rapid Custom Attribute extraction.</remarks>
public static bool TryGetCustomAttributes<T>(this ICustomAttributeProvider customAttributeProvider, out T[] value) where T : Attribute
{
return TryGetCustomAttributes<T>(customAttributeProvider, true, out value);
}
#endregion
}
}

As most of the Reflection classes, such as Type, MemberInfo, and ParameterInfo, all implement ICustomAttributeProvider, you can add some extension methods (new to C# 3.0 and Visual Basic 9.0) to extend this interface to make retrieving attributes a little easier.

For example:

[C#]

using System;
using System.Reflection;

public static class CustomAttributeProviderExtensions
{
    public static T[] GetCustomAttributes<T>(this ICustomAttributeProvider provider) where T : Attribute
    {
        return GetCustomAttributes<T>(provider, true);
    }

    public static T[] GetCustomAttributes<T>(this ICustomAttributeProvider provider, bool inherit) where T : Attribute
    {
        if (provider == null)
            throw new ArgumentNullException("provider");

        T[] attributes = provider.GetCustomAttributes(typeof(T), inherit) as T[];
        if (attributes == null)
        {   // WORKAROUND: Due to a bug in the code for retrieving attributes
            // from a dynamic generated parameter, GetCustomAttributes can return
            // an instance of an object[] instead of T[], hence the cast above
            // will return null.

            return new T[0];
        }

        return attributes;
    }
}

This allows you to do the following:

[C#]

[Serializable]
class Program
{
    static void Main(string[] args)
    {
        SerializableAttribute[] attributes = typeof(Program).GetCustomAttributes<SerializableAttribute>();

        foreach (var attribute in attributes)
        {
            Console.WriteLine(attribute);
        }
    }
}

Which outputs the following:

SerializableAttribute