I have a label(that's actually a button) named "Register". Users who click on the label are taken to a page in the PowerApp where they type their first and last name in the textbox. When they click the Submit button, it creates a item(row) in SharePoint. I want to make sure they can only write to this list once.
I was thinking that maybe "If (lookup, SPlist, User().FullName = "SPlist".Title", false, true)" should be in the Visible property for the label. "If their is a First and Last name in the Title field already in the Sharepoint List that matches the logged in user (User().FullName), the Register button isnt available"
You could also store the user's ID in the SharePoint list to make this a little more straightforward.
Also, just a thought, instead of altering the Visible property, you could make it do something like this on the registration button's OnSelect() function, which is a little more user friendly. It will notify the user that they have already registered instead of the control just disappearing.
If(LookUp(Splist,User().FullName=SPlist.Title,Title)<>Blank(), Navigate(YourRegistrationForm), Notify("You have already registered.",NotificationType.Information))