tvOS 中是否有用于 Focus Engine 调试的隐藏工具？

Question

我最喜欢的 iOS 隐藏调试工具之一是在 UIView 实例上使用 recursiveDescription。例如，这对于排除可能在屏幕外的视图位置的故障非常有用。在 tvOS 上调试 Focus Engine 会带来一系列挑战，尤其是围绕它认为可聚焦的元素。

tvOS 是否有任何隐藏的调试工具来检查 Focus 引擎内部发生的事情？

Answer 1

有两种有用的方法，它们实际上都记录在 App Programming Guide for tvOS。

UIView

如果您尝试将焦点移动到特定视图但不能，UIView 上有一种调试方法可以帮助解释原因：_whyIsThisViewNotFocusable

此方法的输出如下所示：

(lldb) po [(UIView *)0x148db5234 _whyIsThisViewNotFocusable]
ISSUE: This view has userInteractionEnabled set to NO. Views must allow user interaction to be focusable.
ISSUE: This view returns NO from -canBecomeFocused.

UIFocusUpdateContext

UIFocusUpdateContext 对象支持 Xcode 的 QuickLook 功能，因此如果您在调试器中暂停，您可以按空格键（或单击变量旁边的眼球图标）来查看焦点引擎所见内容的图形表示（图片来自 Apple 的文档）：

Answer 2

从 tvOS 11 开始，对无法访问的项目进行故障排除变得更加容易，只需将其添加到问题 ViewController 的 viewDidLoad 中：

 if #available(tvOS 11.0, *) {
  NotificationCenter.default.addObserver(
    forName: NSNotification.Name.UIFocusMovementDidFail
  ) { [weak self] notification in
    let context = notification.userInfo![UIFocusUpdateContextKey] as! UIFocusUpdateContext
    print(context) // If you add a breakpoint here you can quicklook the context in the debugger for more information
    print(UIFocusDebugger.checkFocusability(for: self!.collectionView)) // replace collectionView with the view you want to check
  }
}

这会导致调试输出如下：

<UIFocusUpdateContext: 0x6080000fe800: previouslyFocusedItem=<UIKeyboard 0x7fc597d75610>, nextFocusedItem=(null), focusHeading=Down>

The following issues were found that would prevent this item from being focusable:
- ISSUE: The item is being visually occluded by the following items:
<UIView 0x7fc597c3a9e0>

tvOS 中是否有用于 Focus Engine 调试的隐藏工具？

Are there any hidden tools in tvOS for Focus Engine debugging?

debugging

tvos

UIView

UIFocusUpdateContext