报错信息:

Your application has presented a UIAlertController (<UIAlertController: 0x100b790f0>) 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.
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ActionSheet样式弹框:

UIAlertController *alert = [UIAlertController alertControllerWithTitle:@"title" message:@"message" preferredStyle:UIAlertControllerStyleActionSheet];UIAlertAction *action = [UIAlertAction actionWithTitle:@"act1" style:UIAlertActionStyleDefault handler:^(UIAlertAction * _Nonnull action) {}];UIAlertAction *action2 = [UIAlertAction actionWithTitle:@"act2" style:UIAlertActionStyleDefault handler:^(UIAlertAction * _Nonnull action) {}];UIAlertAction *cancle = [UIAlertAction actionWithTitle:@"cancle" style:UIAlertActionStyleCancel handler:^(UIAlertAction * _Nonnull action) {}];[alert addAction:action];[alert addAction:action2];[alert addAction:cancle];[self presentViewController:alert animated:YES completion:nil];
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设置仅在iPhone: 路径: TARGETS -> Development Info -> Devices

上面创建UIAlertControllerStyleActionSheet样式弹框的代码在iPhone手机上运行时没有问题，运行效果如图(四周存在黑边是因为Xcode设置仅在iPhone运行 而模拟器放在了iPad上不适配所致): 此时可看到UIAlertControllerStyleActionSheet运行效果iPhone与iPad效果一致.

设置Universal:

设置机型为Universal(即: 手机和iPad均支持) 在iPhone上运行效果与上一致，而在iPad上运行时 导致崩溃

解决:

UIAlertController *alert = [UIAlertController alertControllerWithTitle:@"title" message:@"message" preferredStyle:UIAlertControllerStyleActionSheet];UIAlertAction *action = [UIAlertAction actionWithTitle:@"act1" style:UIAlertActionStyleDefault handler:^(UIAlertAction * _Nonnull action) {}];UIAlertAction *action2 = [UIAlertAction actionWithTitle:@"act2" style:UIAlertActionStyleDefault handler:^(UIAlertAction * _Nonnull action) {}];UIAlertAction *cancle = [UIAlertAction actionWithTitle:@"cancle" style:UIAlertActionStyleCancel handler:^(UIAlertAction * _Nonnull action) {}];[alert addAction:action];[alert addAction:action2];[alert addAction:cancle];UIPopoverPresentationController *popover = alert.popoverPresentationController;if (popover){popover.sourceView = self.view;popover.sourceRect = CGRectMake(0, 0, 100, 100);popover.permittedArrowDirections = UIPopoverArrowDirectionAny;}[self presentViewController:alert animated:YES completion:nil];
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