XObject.Changed Event


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Raised when this XObject or any of its descendants have changed.

Namespace:   System.Xml.Linq
Assembly:  System.Xml.Linq (in System.Xml.Linq.dll)

member Changed : IEvent<EventHandler<XObjectChangeEventArgs>,

Events are raised only when an XML tree is modified, not when it is constructed. This is because you have to add an event handler to an event before you can receive events, and you cannot add an event handler before you have a reference to an XObject. You cannot get a reference to an XObject before the XML tree is constructed. This means that during functional construction of an XML tree, you will not receive events.

You should be careful when modifying an XML tree within one of these events, because doing this might lead to unexpected results. For example, if you receive a Changing event, and while the event is being processed you remove the node from the tree, you might not receive the Changed event. When an event is being processed, it is valid to modify an XML tree other than the one that contains the node that is receiving the event; it is even valid to modify the same tree provided the modifications do not affect the specific nodes on which the event was raised. However, if you modify the area of the tree that contains the node receiving the event, the events that you receive and the impact to the tree are undefined.

The following example adds an event handler to the root element of an XML tree. It then modifies the tree, causing LINQ to XML to raise some events.

No code example is currently available or this language may not be supported.

This example produces the following output:

                Changing event raised
  Sender: Child
  ObjectChange: Add
Changed event raised
  Sender: Child
  ObjectChange: Add

Events are useful when you want to maintain some aggregate information in an XML tree. For example, you may want maintain an invoice total that is the sum of the line items of the invoice. This example uses events to maintain the total of all of the child elements under the complex element Items.

No code example is currently available or this language may not be supported.

This code produces the following output:

                Changed System.Xml.Linq.XElement Add
Changed System.Xml.Linq.XElement Add
Changed System.Xml.Linq.XText Remove
Changed System.Xml.Linq.XText Add
Changed System.Xml.Linq.XElement Add
Changed System.Xml.Linq.XElement Remove
Changed System.Xml.Linq.XElement Add

Universal Windows Platform
Available since 8
.NET Framework
Available since 3.5
Portable Class Library
Supported in: portable .NET platforms
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
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