It contains information that can be relevant for both the sender (the object that raises the event) and the receiver (the object that handles it) or only one of them,
Sometime, the EventArgs contains information that is created by the sender and is read-only to the receiver. Consider the X and Y arguments of an ImageClickEventArgs class for example. They can't be changed by the receiver.
In other cases, the receiver can change the information on the EventArgs so the sender can do soemthing with that information. For example, event args classes that expose a Cancel property enable the receiver to determine whether the sender should continue with some action or not.
Hope this helps,
Imar
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