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If you set the text for the cancel button in the initializer, iOS will take care of this for you.
As the Human Interface Guidelines say:
In a two-button alert that proposes a potentially risky action, the button that cancels the action should be on the right (and light-colored).
Although, in practice, you may be labeling your buttons with something other than the generic label. (I have Yes/No) alerts in many circumstances. As your example from Apple shows, this part of the HIG won't be a deal breaker for your app.