macOS 上的 iOS 应用程序不显示 UIAlertController

Question

我有一个 iOS 应用程序，在 macOS 上运行时会显示警报以响应用户操作。

let alertController = UIAlertController(title: "Choose an action", message: nil, preferredStyle: .actionSheet)

alertController.addAction(UIAlertAction(title: "Cancel", style: .cancel) { _ in
    // ...
})
alertController.addAction(UIAlertAction(title: "Action 1", style: .default, handler: { _ in
    // ...
}))
alertController.addAction(UIAlertAction(title: "Action 2", style: .default, handler: { _ in
    // ...
}))

present(alertController, animated: true, completion: nil)

这会因错误而崩溃：

您的应用程序已呈现来自ExampleViewController () 的UIAlertControllerStyleActionSheet 样式的UIAlertController ()。具有此样式的 UIAlertController 的 modalPresentationStyle 是 UIModalPresentationPopover。您必须通过警报控制器的 popoverPresentationController 提供此弹出窗口的位置信息。您必须提供 sourceView 和 sourceRect 或 barButtonItem。如果在呈现警报控制器时不知道此信息，您可以在 UIPopoverPresentationControllerDelegate 方法 -prepareForPopoverPresentation 中提供它。

在 iOS 或 iPadOS 上运行时，不需要在 popoverPresentationController 上设置属性，因为它使用 actionSheet 样式。此视图控制器无法访问 UIBarButtonItem，因此无法设置 barButtonItem 属性。如果我设置了 sourceView 和 sourceRect 属性（如下所示），它会记录自动布局错误并且不显示警报：

if #available(iOS 14.0, *), ProcessInfo.processInfo.isiOSAppOnMac {
    alertController.popoverPresentationController?.sourceView = view
    alertController.popoverPresentationController?.sourceRect = view.bounds
}

[LayoutConstraints] Unable to simultaneously satisfy constraints.
    Probably at least one of the constraints in the following list is one you don't want. 
    Try this: 
        (1) look at each constraint and try to figure out which you don't expect; 
        (2) find the code that added the unwanted constraint or constraints and fix it. 
    (Note: If you're seeing NSAutoresizingMaskLayoutConstraints that you don't understand, refer to the documentation for the UIView property translatesAutoresizingMaskIntoConstraints) 
(
    "<NSAutoresizingMaskLayoutConstraint:0x600003a1a3a0 h=--& v=--& UIView:0x12914af30.height == 13   (active)>",
    "<NSLayoutConstraint:0x600003a1f750 UIView:0x129067d90.height >= 44   (active)>",
    "<NSLayoutConstraint:0x600003a1fed0 _UIAlertControllerView:0x1290677a0'Choose an action'.height == UIView:0x129067d90.height   (active)>",
    "<NSLayoutConstraint:0x600003a19040 UIView:0x12914af30.height == _UIAlertControllerView:0x1290677a0'Choose an action'.height   (active)>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x600003a1f750 UIView:0x129067d90.height >= 44   (active)>

Make a symbolic breakpoint at UIViewAlertForUnsatisfiableConstraints to catch this in the debugger.
The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKitCore/UIView.h> may also be helpful.

[LayoutConstraints] Unable to simultaneously satisfy constraints.
    Probably at least one of the constraints in the following list is one you don't want. 
    Try this: 
        (1) look at each constraint and try to figure out which you don't expect; 
        (2) find the code that added the unwanted constraint or constraints and fix it. 
    (Note: If you're seeing NSAutoresizingMaskLayoutConstraints that you don't understand, refer to the documentation for the UIView property translatesAutoresizingMaskIntoConstraints) 
(
    "<NSAutoresizingMaskLayoutConstraint:0x600003a1a350 h=--& v=--& UIView:0x12914af30.width == 0   (active)>",
    "<NSLayoutConstraint:0x600003a4e0d0 UIView:0x129067d90.width == 270   (active)>",
    "<NSLayoutConstraint:0x600003a1fe80 _UIAlertControllerView:0x1290677a0'Choose an action'.width >= UIView:0x129067d90.width   (active)>",
    "<NSLayoutConstraint:0x600003a18ff0 UIView:0x12914af30.width == _UIAlertControllerView:0x1290677a0'Choose an action'.width   (active)>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x600003a4e0d0 UIView:0x129067d90.width == 270   (active)>

Make a symbolic breakpoint at UIViewAlertForUnsatisfiableConstraints to catch this in the debugger.
The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKitCore/UIView.h> may also be helpful.

How can I use UIAlertController 在 macOS 上运行的 iOS 应用程序中？请注意：这不是 Catalyst 应用程序，这是在 Apple Silicon Mac 上本地运行的 iOS 应用程序。