Merge pull request #573 from euju-ms/aot

Fix AOT warning with HtmlNode.GetAttributeValue

src/HtmlAgilityPack.Shared/HtmlNode.cs

@@ -1392,7 +1392,7 @@ public string GetAttributeValue(string name, string def)
 
 			return att.Value;
 #else
-			return GetAttributeValue<string>(name, def);
+			return GetAttributeValue<string>(name, def, null);
 #endif
         } 
 
@@ -1430,7 +1430,7 @@ public int GetAttributeValue(string name, int def)
 				return def;
 			}
 #else
-			return GetAttributeValue<int>(name, def);
+			return GetAttributeValue<int>(name, def, int.TryParse);
 #endif
 		}
 
@@ -1468,7 +1468,7 @@ public bool GetAttributeValue(string name, bool def)
 				return def;
 			}
 #else
-			return GetAttributeValue<bool>(name, def);
+			return GetAttributeValue<bool>(name, def, bool.TryParse);
 #endif
 		}
 
@@ -1481,11 +1481,12 @@ public bool GetAttributeValue(string name, bool def)
 		/// <param name="name">The name of the attribute to get. May not be <c>null</c>.</param>
 		/// <param name="def">The default value to return if not found.</param>
 		/// <returns>The value of the attribute if found, the default value if not found.</returns>
+		[Obsolete("Use GetAttributeValue with an explicit custom parser for AOT compatibility")]
 		public T GetAttributeValue<T>(string name, T def) 
 		{
 			if (name == null)
 			{
-				throw new ArgumentNullException("name");
+				throw new ArgumentNullException(nameof(name));
 			}
 
 			if (!HasAttributes)
@@ -1508,6 +1509,51 @@ public T GetAttributeValue<T>(string name, T def)
 				return def;
 			}
 		}
+
+		/// <summary>
+		/// Parser for attribute value.
+		/// </summary>
+		/// <typeparam name="T">The type to parse string value into</typeparam>
+		public delegate bool AttributeValueParser<T>(string value, out T result);
+
+		/// <summary>
+		/// Helper method to get the value of an attribute of this node as type T. If the attribute is not found
+		/// or if the attribute is not parsable to type T, the default value will be returned.
+		/// </summary>
+		/// <param name="name">The name of the attribute to get. May not be <c>null</c>.</param>
+		/// <param name="def">The default value to return if not found.</param>
+		/// <param name="parser">The parser used to convert string attribute value to T.</param>
+		/// <returns>The value of the attribute if found and parsable, the default value otherwise.</returns>
+		public T GetAttributeValue<T>(string name, T def, AttributeValueParser<T> parser)
+		{
+			if (name == null)
+			{
+				throw new ArgumentNullException(nameof(name));
+			}
+
+			if (!HasAttributes)
+			{
+				return def;
+			}
+
+			HtmlAttribute att = Attributes[name];
+			if (att?.Value == null)
+			{
+				return def;
+			}
+
+			if (att.Value is T value)
+			{
+				return value;
+			}
+
+			if (parser != null && parser(att.Value, out T parsedValue))
+			{
+				return parsedValue;
+			}
+
+			return def;
+		}
 #endif
 
 		/// <summary>