ios - UIAlertController 中的 UIPickerView 仅在 iPad 中给出错误，而在 iPhone 中正确？

Question

我使用以下代码进行警报 View ，它在 iPhone 中工作。但是当我在 iPad 上运行它时，出现以下错误:

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.'

警报 View 的代码如下:

let alertView = UIAlertController(title: "Select Launguage", message: "\n\n\n\n\n\n\n\n\n\n", preferredStyle: UIAlertControllerStyle.ActionSheet);

   pickerView.center.x = self.view.center.x

    alertView.view.addSubview(pickerView)

    let action = UIAlertAction(title: "OK", style: UIAlertActionStyle.Default, handler: nil)

    alertView.addAction(action)
    presentViewController(alertView, animated: true, completion: nil)

请帮助我。为什么它不能在 iPad 上运行...

Answer 1

在 iPad 上，警报将使用 UIPopoverPresentationController 显示为弹出窗口，它要求您指定用于呈现弹出窗口的 anchor 。

UIViewController *self; // code assumes you're in a view controller
UIButton *button; // the button you want to show the popup sheet from

UIAlertController *alertController;
UIAlertAction *destroyAction;
UIAlertAction *otherAction;

alertController = [UIAlertController alertControllerWithTitle:nil
                                                      message:nil
                           preferredStyle:UIAlertControllerStyleActionSheet];
destroyAction = [UIAlertAction actionWithTitle:@"Remove All Data"
                                         style:UIAlertActionStyleDestructive
                                       handler:^(UIAlertAction *action) {
                                           // do destructive stuff here
                                       }];
otherAction = [UIAlertAction actionWithTitle:@"Blah"
                                       style:UIAlertActionStyleDefault
                                     handler:^(UIAlertAction *action) {
                                         // do something here
                                     }];
// note: you can control the order buttons are shown, unlike UIActionSheet
[alertController addAction:destroyAction];
[alertController addAction:otherAction];
[alertController setModalPresentationStyle:UIModalPresentationPopover];

UIPopoverPresentationController *popPresenter = [alertController 
                                              popoverPresentationController];
popPresenter.sourceView = button;
popPresenter.sourceRect = button.bounds;
[self presentViewController:alertController animated:YES completion:nil];