Serializing/Deserializing an ArrayList to be an XML file

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C#

Hi, I am writing a windows form application with C#.

There is one ArrayList which includes several objects. And I successfully wrote code to serialize this ArrayList to be an XML file, and can deserialize this XML to back to ArrayList.

However, the above process is based on the assumption that I know the length(number) of objects when doing serialization or deserialization.

The question and problem now is :
How can I know the length(number) of objects in an exited XML file (including serialized ArrayList) before I would first deserialize it ? Since the instruction below need a DataType to match the length of objects ?

Type[ ] DataType = new Type[ ? ]  // how can I know the lenght ?
XmlSerializer xs_load = new XmlSerializer(typeof(ArrayList), DataType);