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

Question

我使用以下代码警报视图，它在iPhone中工作。但是当我在iPad中运行它时，它会出现以下错误：

由于未捕获的异常“NSGenericeException”而终止应用程序，原因：“您的应用程序已呈现UIAlertControllerStyleActionSheet样式的UIAlertController（）。具有此样式的UIAlertController的modalPresentationStyle为UIModalPresentationPopover。您必须通过警报控制器的popoverPresentationController提供此popover的位置信息。必须提供sourceView和sourceRect或barButtonItem。如果在演示警报控制器时不知道此信息，则可以在UIPopoverPresentationControllerDelegate方法-PrepareForPoverPresentation中提供此信息。”

警报视图代码如下：

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)

请帮帮我。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popover，它要求您为popover的显示指定一个锚点。

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];