iOS开发bug消灭之：Your application has presented a UIAlertController of style ...

Your application has presented a UIAlertController of style UIAlertControllerStyleActionSheet.

swift版本：3.0
Xcode版本：8.0

错误全文：

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.

错误原因：

在页面中设置了actionSheet类型的Alert，在iPhone环境可以正常显示，如下。但是在iPad环境下会报以上错误。原因是iPad上的actionSheet样式会直接转换为popover样式，如果不提前设置好popover样式的话，iPad就不知道如何显示，进而报错

错误源码：

    let optionMenu = UIAlertController(title: nil, message: "请设置头像", preferredStyle: .actionSheet)let getPictureFromLibraryButton = UIAlertAction(title: "打开图库", style: .default, handler: nil )let cancelButton = UIAlertAction(title: "取消", style: .cancel, handler: nil)optionMenu.addAction(getPictureFromLibraryButton)optionMenu.addAction(cancelButton)self.present(optionMenu, animated: true, completion: nil)

修正源码：

方法一：

 let optionMenu = UIAlertController(title: nil, message: "请设置头像", preferredStyle: .actionSheet)let getPictureFromLibraryButton = UIAlertAction(title: "打开图库", style: .default, handler: nil )let cancelButton = UIAlertAction(title: "取消", style: .cancel, handler: nil)optionMenu.addAction(getPictureFromLibraryButton)optionMenu.addAction(cancelButton)// support iPadoptionMenu.popoverPresentationController?.sourceView = self.viewoptionMenu.popoverPresentationController?.sourceRect = (tableView.cellForRow(at: indexPath)?.frame)!self.present(optionMenu, animated: true, completion: nil)</code>

方法二：

 let optionMenu = UIAlertController(title: nil, message: "请设置头像", preferredStyle: .actionSheet)let getPictureFromLibraryButton = UIAlertAction(title: "打开图库", style: .default, handler: nil )let cancelButton = UIAlertAction(title: "取消", style: .cancel, handler: nil)optionMenu.addAction(getPictureFromLibraryButton)optionMenu.addAction(cancelButton)      // support iPadoptionMenu.popoverPresentationController?.barButtonItem = self.saveBarButtomItemself.present(optionMenu, animated: true, completion: nil)

注意事项：

方法一和二必须选定一个
.sourceView 用来指定用来显示popover的view
.sourceRect 用来指定popover的箭头指向哪里，参数是一个矩形。我的源码中是点一个tableView的Cell后弹出Alert，所以我这里传入的就是就是我所点击cell的Rect，效果如下

.barButtonItem只需指定按钮即可，剩下的事系统会自动完成，效果如下