Hi
I think u need learn Asp Page Life cycle.
In btnAdd click event u write btnSave button enable as true,but in page not post back event u again btnSave button enable as false ? why ?
Finally what u get when page open btnSave button is enabled,when u click btnAdd then btnSave button will disabled,bcz u disable save button in page not post back event.
I think ur need is ,when page open need to disable save button and textbox,when click add button need to enable save button and textbox,if yes means,in postback event u add save button and textbox disable code and in not postback event u add save button and textbox enable code
and try update panel for not refresh page
https://msdn.microsoft.com/en-us/library/bb399001.aspx[
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https://msdn.microsoft.com/en-us/library/bb386454.aspx[
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Put ur control inside update panel,then only controls update ,i mean button enable and disable without page refersh