如何修复iOS 12.x中[_UIStatusBarDisplayItemState updatePlacement]崩溃问题？

Hey, I’ve run into this exact iOS 12-exclusive crash before, so I can walk you through what’s going on and how to fix it.

First, let’s recap the key details to make sure we’re on the same page:

• Crash triggers in the private framework method [_UIStatusBarDisplayItemState updatePlacement]
• The error message thrown is:

  "The item state should have been data updated before updating its placement"

• This only pops up on iOS 12.x versions—later iOS iterations fixed this internal logic constraint.

Why this happens #

iOS 12 has a stricter order of operations for status bar updates compared to newer iOS versions. The system expects that any status bar item’s data is fully updated before you try to adjust its placement or layout. If your code (or a third-party library you’re using) triggers a layout update for a status bar item before its data is ready, this crash fires.

How to fix it #

Here are actionable steps to resolve this:

• Audit all status bar-related code in your project: This includes custom status bar views, code that modifies status bar style, or KVO observers that watch status bar properties.
• Reorder your update logic: Make sure you complete all data updates for the status bar item first, then trigger any layout-related calls (like setNeedsLayout or layoutIfNeeded). For example, if you’re updating a custom status bar label’s text, set the text before adjusting its frame or layout constraints.
• Check third-party libraries: If the crash comes from a dependency, look for iOS 12-specific fixes in the library’s release notes. If there’s no official patch, you might need to fork the library and adjust the order of data vs. layout updates in its status bar code.
• Delay layout updates to the next runloop: If you can’t easily reorder the code, wrap your layout update calls in DispatchQueue.main.async to ensure they run after any pending data updates on the main thread. Example:

  // First update your data
  customStatusBarItem.data = updatedData
  // Then delay layout to next runloop
  DispatchQueue.main.async {
      customStatusBarItem.setNeedsLayout()
  }
  

After making these changes, be sure to test specifically on an iOS 12 device or simulator to confirm the crash is resolved.

内容的提问来源于stack exchange，提问作者xiaotao Li