VB.net TextChanged event does not fire on keypress

I am creating a website and I have a textbox that is filled from a DB. I want to lock the contents so to speak but allow the user to add data to the text box but not edit the original text. I thought I would use the textcahnged event but it does not fire until you are leaving the page?

Is there no way to do this at the textbox does not have any other usable events that I can see. I know how I want to do it just not where.

 

Thanks,

Ty
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