UIAlertController在ipad上运行崩溃（ UIAlertController (<UIAlertController: 0x1099a7800>) of style UIAlertControllerStyleActionSheet. The modalPresentationStyle of a UIAlertController with this style is UIMo）

当使用UIAlertController的

UIAlertControllerStyleActionSheet

时在ipad上运行会崩溃，报以下的错误：

 reason: 'Your application has presented a UIAlertController (<UIAlertController: 0x1099a7800>) 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.

意思就是没有设置UIAlertController这个弹出窗口的位置信息，可以通过下面的方式解决，

alertSheetVc.popoverPresentationController.sourceView = self.bgScrollView; 

alertSheetVc.popoverPresentationController.sourceRect =  view.frame;

 或者是通过实现 UIPopoverPresentationControllerDelegate的prepareForPopoverPresentation方法 来设置UIAlertController在当前页面上的位置信息，设置后的显示效果与 iPhone是有区别的不是在屏幕的中间位置弹出而是在你所设置的位置弹出：如下图的界面效果

UIAlertController *alertSheetVc = [UIAlertController alertControllerWithTitle:nil message:nil preferredStyle:UIAlertControllerStyleActionSheet];
    alertSheetVc.popoverPresentationController.sourceView = self.bgScrollView;
    
    alertSheetVc.popoverPresentationController.sourceRect =  view.frame;
    
    UIAlertAction *cancelAction = [UIAlertAction actionWithTitle:@"取消" style:UIAlertActionStyleCancel handler:^(UIAlertAction * _Nonnull action) {
        
    }];
    UIAlertAction *albumAction = [UIAlertAction actionWithTitle:@"去相册选择" style:UIAlertActionStyleDefault handler:^(UIAlertAction * _Nonnull action) {
        [self pushTZImagePickerController];
    }];
    UIAlertAction *cameraAction = [UIAlertAction actionWithTitle:@"拍照" style:UIAlertActionStyleDefault handler:^(UIAlertAction * _Nonnull action) {
        [self takePhoto];
    }];
    [alertSheetVc addAction:cameraAction];
    [alertSheetVc addAction:albumAction];
    [alertSheetVc addAction:cancelAction];
    [self presentViewController:alertSheetVc animated:YES completion:nil];