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)
}

如果你在点击UIBarButtonItem时显示UIActivityViewController，请使用以下代码:

activityViewController.popoverPresentationController?.barButtonItem = sender

否则，如果你使用另一个控件，例如UIButton，使用以下代码:

activityViewController.popoverPresentationController?.sourceView = sender
activityViewController.popoverPresentationController?.sourceRect = sender.bounds

从文档到UIPopoverPresentationController:

var barButtonItem: UIBarButtonItem? { get set }

为此属性分配一个值，以将弹出窗口锚定到指定的栏按钮项。显示时，弹出窗口的箭头指向指定的项。或者，您可以使用sourceView和sourceRect属性为弹出窗口指定锚点位置。

Swift = ios7/ ios8

let activityViewController = UIActivityViewController(activityItems: sharingItems, applicationActivities: nil)

//if iPhone
if (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiom.Phone) {
    // go on..
} else {
    //if iPad
    if activityViewController.respondsToSelector(Selector("popoverPresentationController")) {
        // on iOS8
        activityViewController.popoverPresentationController!.barButtonItem = self.shareButtonItem;
    }
}
self.presentViewController(activityViewController, animated: true, completion: nil)

在Swift修复这个iPad，最好的方法是这样做，我发现。

    let things = ["Things to share"]
    let avc = UIActivityViewController(activityItems:things, applicationActivities:nil)
    avc.setValue("Subject title", forKey: "subject")
    avc.completionWithItemsHandler = {
        (s: String!, ok: Bool, items: [AnyObject]!, err:NSError!) -> Void in
    }

    self.presentViewController(avc, animated:true, completion:nil)
    if let pop = avc.popoverPresentationController {
        let v = sender as! UIView // sender would be the button view tapped, but could be any view
        pop.sourceView = v
        pop.sourceRect = v.bounds
    }

迅速:

    let activityViewController = UIActivityViewController(activityItems: sharingItems, applicationActivities: nil)

    //if iPhone
    if (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiom.Phone) {
        self.presentViewController(activityViewController, animated: true, completion: nil)
    } else { //if iPad
        // Change Rect to position Popover
        var popoverCntlr = UIPopoverController(contentViewController: activityViewController)
        popoverCntlr.presentPopoverFromRect(CGRectMake(self.view.frame.size.width/2, self.view.frame.size.height/4, 0, 0), inView: self.view, permittedArrowDirections: UIPopoverArrowDirection.Any, animated: true)

    }

在iPad上，活动视图控制器将显示为一个弹出窗口使用新的UIPopoverPresentationController，它要求你指定一个锚点为弹出窗口的表示使用以下三个属性之一:

栏按钮项 源视图 源矩形

为了指定锚点，你需要获得UIActivityController的UIPopoverPresentationController的引用，并设置其中一个属性如下所示:

if ( [activityViewController respondsToSelector:@selector(popoverPresentationController)] ) { 
// iOS8
 activityViewController.popoverPresentationController.sourceView =
parentView;
 }