override this function in UITextView subclass.override func canPerformAction(_ action: Selector, withSender sender: Any?) -> Bool {
switch action {
case #selector(UIResponderStandardEditActions.paste(_:)),
#selector(UIResponderStandardEditActions.select(_:)),
#selector(UIResponderStandardEditActions.selectAll(_:)),
#selector(UIResponderStandardEditActions.copy(_:)),
#selector(UIResponderStandardEditActions.cut(_:)),
#selector(UIResponderStandardEditActions.delete(_:)) :
return false
default:
return true
}
return false
}