modal windows – Do you need a close button to dismiss iPhone sheets?

In iPhone, you can dismiss a sheet (popup) by swiping down on it. Is adding a close button (x on a corner) also necessary? Do you think iPhone users will know that that’s how you dismiss it?

I have a few sheets on my app, most have a “Save” type button at the bottom that saves changes and dismisses the sheet, but if you pull down on it and dismiss it, the changes are lost (kind of a cancel mechanism). I’m not sure if people will know that they can dismiss the sheet by pulling it as a sort of cancel button.

I guess adding the button wouldn’t hurt, but I also don’t want to be redundant.