Hi,
When the FileValidating be fired, the file data have been uploaded completely.
You can validate the file data and do something there.
The difference between FileValidating and FileUploaded,
Is that FileValidating is in another page life cycle and any UI changes would not take effects.
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In the FileValidating or FileUploaded,
You can use the argument 'args' to get the temp path of the file, and you can also get the filename.
Regards,
Terry