I am currently writing a form where I needed to highlight and select all text in a textbox when it is selected (onfocus), cause that is what user will be doing: copy and paste, so that in effect requires selecting the whole text string currently in the textbox, to replace it with new value.
I got two answers from my search routing, server side, and client side, and that is coming from a single article.
In Page_Load event, add below code:
The other way is what I tested, and it worked, so I assume above works as well:
Hoe this helps you, as it did me.
Till then. Ciao!
Reference: selectall() property in C# for textbox control