AjaxFileUpload

I need to save the file uploaded using AjaxFileUpload on button click only. How can I pass an object of the fileUploader to the Button click function on the aspx.cs page..??

We can save the file uploaded using AjaxFileUpload on the function called by the uploader on its UploadComplete. I know that and I know how it works. 

But I want to save the file uploaded only on my button click. Whenever i put the file save code on the button click event on aspx.cs file, am getting an error, "Object reference not set to an instance of an object"

Please help me. Am stuck on this part for nearly 3 weeks.