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Common/DTS.Common.Utilities/AttributeExtractor.cs

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+/*
+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);
+            }
+        }
+    }
+}