enable/disable a button on the page

I hope someone can help me to figure it out
On my page, I have one FormView and TextBox and a button.
in the FormView, when it is on ItemTemplate, there are a 'Edit' and  a 'Delete' linkedbutton, if I click Edit linkedbutton, FormView changed to EditItemTemplate in which there are two linkedbuttons, 'Update' and 'Cancel'
Outside FormView, I have a TextBox and a Button called 'Add' which can add content of textBox to a database.
Question: When page load, the button 'Add' I set it to disable while FormView is on the ItemTemplate mode, I want to this 'add' button enable after I click the linkedbutton 'Edit' and After I click linkedbutton 'Update' which is in the EditItemTemplate mode in FormView, the 'Add' button on the page will change to disable.
How can I do this?
Thanks.
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