Removing Attributes from an Element Node in the DOM
There are many ways to remove attributes. One technique is to remove them from the attribute collection. To do this, the following steps are performed:
- Get the attribute collection from the element using
XmlAttributeCollection attrs = elem.Attributes;. - Remove the attribute from the attribute collection using one of three methods:
- Use XmlAttributeCollection.Remove Method to remove a specific attribute.
- Use XmlAttributeCollection.RemoveAll Method to remove all attributes from the collection and leave the element with no attributes.
- Use XmlAttributeCollection.RemoveAt Method to remove an attribute from the attribute collection by using its index number.
The following methods remove attributes from the element node.
- Use XmlElement.RemoveAllAttributes to remove the attribute collection.
- Use XmlElement.RemoveAttribute Method to remove a single attribute by name from the collection.
- Use XmlElement.RemoveAttributeAt to remove a single attribute by index number from the collection.
One more alternative is to get the element, get the attribute from the attribute collection, and remove the attribute node directly. To get the attribute from the attribute collection, you can use a name, XmlAttribute attr = attrs["attr_name"];, an index XmlAttribute attr = attrs[0];, or by fully qualifying the name with the namespace XmlAttribute attr = attrs["attr_localName", "attr_namespace"].
Regardless of the method used to remove attributes, there are special limitations on removing attributes that are defined as default attributes in the DTD. Default attributes cannot be removed unless the element they belong to is removed. Default attributes are always be present for elements that have default attributes declared. Removing a default attribute from an XmlAttributeCollection or from the XmlElement results in a replacement attribute inserted into the XmlAttributeCollection of the element, initialized to the default value that was declared. If you have an element defined as <book att1="1" att2="2" att3="3"></book>, then you have a book element with three default attributes declared. The DOM implementation guarantees that as long as this book element exists, it will have these three default attributes of att1, att2, and att3.
When called with an XmlAttribute, the RemoveAll sets the value of the attribute to String.Empty, as an attribute cannot exist without a value.