DP44/Common/DTS.Common.Utilities/AttributeExtractor.cs

/*
AttributeExtractor.cs

Copyright © 2008
Diversified Technical Systems
All Rights Reserved
*/

using System;
using System.Collections.Generic;
using System.Reflection;

namespace DTS.Common.Utilities
{
    /// <summary>
    /// Class to ease extracting custom attributes from their attached objects.
    /// </summary>
    /// <typeparam name="TAttributeType"></typeparam>
    public class AttributeExtractor<TAttributeType> : Exceptional
    {
        /// <summary>
        /// Extract an attribute of this class' declared type from the specified target.
        /// </summary>
        /// 
        /// <param name="target">
        /// The <see cref="Object"/> to which the sought attribute is attached.
        /// </param>
        /// 
        /// <returns>
        /// The attribute type specified upon AttributeExtractor creation.
        /// </returns>
        /// 
        public TAttributeType ExtractAttachedAttributeFromObject(object target)
        {
            try
            {
                ICustomAttributeProvider info = target.GetType();
                var attributes = info.GetCustomAttributes(typeof(TAttributeType), false) as TAttributeType[];
                if (attributes != null)
                {
                    if (attributes.Length < 1)
                        throw new Exception("attempted to extract non-existent \"" + typeof(TAttributeType) + "\" attribute");
                    if (attributes.Length > 1)
                        throw new Exception("attempted to extract \"" + typeof(TAttributeType) + "\" attribute from object decorated with multiple attributes; there should be only one");
                }
                return attributes[0];
            }

            catch (System.Exception ex)
            {
                string targetString;
                throw new Exception("encountered problem extracting attached \"" + typeof(TAttributeType) + "\"attribute value from object " + (null != (targetString = target.ToString()) ? ("\"" + targetString + "\"") : "<<NULL>>"), ex);
            }
        }

        /// <summary>
        /// Extract a list of attached attributes from the specified property.  An object and property name
        /// must be supplied, for attempts to directly reference the property will result in get/set invocation.
        /// </summary>
        /// 
        /// <param name="propertyContainer">
        /// The <see cref="Object"/> that contains the property under query.
        /// </param>
        /// 
        /// <param name="propertyName">
        /// The <see cref="string"/> name of the property to be queried.
        /// </param>
        /// 
        /// <returns>
        /// A <see cref="T:List"/> of attached attributes of the type specified during the creation
        /// of this instance of AttributeExtractor.
        /// </returns>
        /// 
        public List<TAttributeType> ExtractAttachedAttributesFromProperty(object propertyContainer, string propertyName)
        {
            try
            {
                if (null == propertyContainer)
                    throw new ArgumentNullException("cannot extract property from null property container reference");
                if (string.IsNullOrEmpty(propertyName))
                    throw new ArgumentException("cannot extract property with null/empty string name");
                try
                {
                    return new List<TAttributeType>(propertyContainer.GetType().GetProperty(propertyName).GetCustomAttributes(typeof(TAttributeType), false) as TAttributeType[]);
                }
                catch (NullReferenceException)
                {
                    throw new Exception("attribute does not exist");
                }
            }

            catch (System.Exception ex)
            {
                string propertyContainerString;
                throw new Exception("encountered problem extracting attached XML tag attribute values from property " + (null != propertyName ? ("\"" + propertyName + "\"") : "<<NULL>>") + " on object " + (null != (propertyContainerString = propertyContainer.ToString()) ? ("\"" + propertyContainerString + "\"") : "<<NULL>>"), ex);
            }
        }

        /// <summary>
        /// Extract an attached attributes from the specified property of the type declared during the
        /// creation of this instance of AttributeExtractor.  An object and property name must be supplied,
        /// for attempts to directly reference the property will result in get/set invocation.
        /// </summary>
        /// 
        /// <param name="propertyContainer">
        /// The <see cref="Object"/> that contains the property under query.
        /// </param>
        /// 
        /// <param name="propertyName">
        /// The <see cref="string"/> name of the property to be queried.
        /// </param>
        /// 
        /// <returns>
        /// An attribute of the type specified during the creation of this instance of AttributeExtractor,
        /// if one is attached; null otherwise.
        /// </returns>
        /// 
        public TAttributeType ExtractAttachedAttributeFromProperty(object propertyContainer, string propertyName)
        {
            try
            {
                if (null == propertyContainer)
                    throw new ArgumentNullException("cannot extract property from null property container reference");
                if (string.IsNullOrEmpty(propertyName))
                    throw new ArgumentException("cannot extract property with null/empty string name");
                var attributes = ExtractAttachedAttributesFromProperty(propertyContainer, propertyName);
                if (attributes.Count < 1)
                    throw new Exception("attempted to extract non-existent \"" + typeof(TAttributeType) + "\" attribute");
                if (attributes.Count > 1)
                    throw new Exception("attempted to extract \"" + typeof(TAttributeType) + "\" attribute from object decorated with multiple attributes; there should be only one");
                return attributes[0];
            }

            catch (System.Exception ex)
            {
                string propertyContainerString;
                throw new Exception("encountered problem extracting attached XML tag attribute value from property " + (null != propertyName ? ("\"" + propertyName + "\"") : "<<NULL>>") + " on object " + (null != (propertyContainerString = propertyContainer.ToString()) ? ("\"" + propertyContainerString + "\"") : "<<NULL>>"), ex);
            }
        }
    }
}