请问一个问题，我在iphone上datepicker弹出来了但是在pad上就崩溃了白了如下的错误，是怎么回事？
2015-11-04 21:04:44.406 JSH[1421:491081] *** Terminating app due to uncaught exception 'NSGenericException', reason: 'Your application has presented a UIAlertController () of style UIAlertControllerStyleActionSheet. The modalPresentationStyle of a UIAlertController with this style is UIModalPresentationPopover. You must provide location information for this popover through the alert controller's popoverPresentationController. You must provide either a sourceView and sourceRect or a barButtonItem. If this information is not known when you present the alert controller, you may provide it in the UIPopoverPresentationControllerDelegate method -prepareForPopoverPresentation.'
*** First throw call stack:
(0x2303167b 0x34c16e17 0x279e11cd 0x27467b3f 0x27465a5f 0x273c60b9 0x273d19eb 0x27113ecd 0x22ff44c9 0x22ff27cd 0x22ff2bff 0x22f46119 0x22f45f05 0x2c0e3ac9 0x27188f15 0x3431a9 0x35385873)
libc++abi.dylib: terminating with uncaught exception of type NSException
