我找到了这个解 首先，你呈现弹窗的视图控制器应该实现<UIPopoverPresentationControllerDelegate>协议。

接下来，你需要设置popoverPresentationController的委托。

添加以下功能:

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
// Assuming you've hooked this all up in a Storyboard with a popover presentation style
    if ([segue.identifier isEqualToString:@"showPopover"]) {
        UINavigationController *destNav = segue.destinationViewController;
        PopoverContentsViewController *vc = destNav.viewControllers.firstObject;

        // This is the important part
        UIPopoverPresentationController *popPC = destNav.popoverPresentationController;
        popPC.delegate = self;
    }
}

- (UIModalPresentationStyle)adaptivePresentationStyleForPresentationController: (UIPresentationController *)controller {
    return UIModalPresentationNone;
}

同样的问题也出现在我的项目中，然后我找到了解决方案，在iPad中打开UIActivityViewController，我们必须使用UIPopoverController

下面是在iPhone和iPad上使用它的代码:

//to attach the image and text with sharing 
UIImage *image=[UIImage imageNamed:@"giraffe.png"];
NSString *str=@"Image form My app";
NSArray *postItems=@[str,image];

UIActivityViewController *controller = [[UIActivityViewController alloc] initWithActivityItems:postItems applicationActivities:nil];

//if iPhone
if (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPhone) {
    [self presentViewController:controller animated:YES completion:nil];
}
//if iPad
else {
    // Change Rect to position Popover
    UIPopoverController *popup = [[UIPopoverController alloc] initWithContentViewController:controller];
    [popup presentPopoverFromRect:CGRectMake(self.view.frame.size.width/2, self.view.frame.size.height/4, 0, 0)inView:self.view permittedArrowDirections:UIPopoverArrowDirectionAny animated:YES];
}

对于swift 4.2 / swift 5

func openShareDilog() {
    let text = "share text will goes here"

    // set up activity view controller
    let textToShare = [text]
    let activityViewController = UIActivityViewController(activityItems: textToShare, applicationActivities: nil)
    activityViewController.excludedActivityTypes = [.airDrop]

    if let popoverController = activityViewController.popoverPresentationController {
        popoverController.sourceRect = CGRect(x: UIScreen.main.bounds.width / 2, y: UIScreen.main.bounds.height / 2, width: 0, height: 0)
        popoverController.sourceView = self.view
        popoverController.permittedArrowDirections = UIPopoverArrowDirection(rawValue: 0)
    }

    self.present(activityViewController, animated: true, completion: nil)
}

修复了Swift 2.0

    if UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiom.Phone {
        self.presentViewController(activityVC, animated: true, completion: nil)
    }
    else {
        let popup: UIPopoverController = UIPopoverController(contentViewController: activityVC)
        popup.presentPopoverFromRect(CGRectMake(self.view.frame.size.width / 2, self.view.frame.size.height / 4, 0, 0), inView: self.view, permittedArrowDirections: UIPopoverArrowDirection.Any, animated: true)
    }

对于Swift 2.0。我发现，如果你试图将弹出窗口锚定在iPad上的共享按钮上，这种方法是有效的。这假设您已经在工具栏中为共享按钮创建了一个出口。

func share(sender: AnyObject) {
    let firstActivityItem = "test"

    let activityViewController = UIActivityViewController(activityItems: [firstActivityItem], applicationActivities: nil)

    if UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiom.Phone {
        self.presentViewController(activityViewController, animated: true, completion: nil)
    }
    else {            
        if activityViewController.respondsToSelector("popoverPresentationController") {
            activityViewController.popoverPresentationController!.barButtonItem = sender as? UIBarButtonItem
            self.presentViewController(activityViewController, animated: true, completion: nil)
        }

    }
}

SwiftUI版本

func presentActivityView(items: [Any]){
    let activityController = UIActivityViewController(activityItems: items, applicationActivities: nil)
    if UIDevice.current.userInterfaceIdiom == .pad{
        activityController.popoverPresentationController?.sourceView = UIApplication.shared.windows.first
        activityController.popoverPresentationController?.sourceRect = CGRect(x:  UIScreen.main.bounds.width / 3, y:  UIScreen.main.bounds.height / 1.5, width: 400, height: 400)
    }
    UIApplication.shared.windows.first?.rootViewController?.present(activityController, animated: true, completion: nil)
}

如果你是在iPad上使用swift进行开发，那么你就得小心了，它在调试时可以正常工作，但在发布时就会崩溃。为了让它与testFlight和AppStore一起工作，禁用swift的优化，使用-none进行发布。