“这个应用程序正在从后台线程修改自动布局引擎”的主要问题是，它似乎在实际问题发生后很长一段时间才被记录下来，这可能会使它很难排除故障。

我设法通过创建三个符号断点来解决这个问题。

调试>断点>创建符号断点…

断点1:

符号:-[UIView setNeedsLayout] 条件:!(BOOL)[NSThread是主线程]

断点2:

符号:-[UIView layoutIfNeeded] 条件:!(BOOL)[NSThread是主线程]

断点3:

符号:-[UIView updateConstraintsIfNeeded] 条件:!(BOOL)[NSThread是主线程]

使用这些断点，您可以很容易地在非主线程上错误地调用UI方法的实际行中获得断点。

对我来说，这个错误消息来自Admob SDK的一个横幅。

我可以通过设置一个条件断点来跟踪原点到“WebThread”。

然后我就可以通过封装Banner的创建来摆脱这个问题:

dispatch_async(dispatch_get_main_queue(), ^{
   _bannerForTableFooter = [[GADBannerView alloc] initWithAdSize:kGADAdSizeSmartBannerPortrait];
   ...
}

我不知道为什么这有帮助，因为我看不出这段代码是如何从一个非主线程调用的。

希望它能帮助到任何人。

在不使用'dispatch_async'的情况下调试print语句时会得到类似的错误消息 因此，当您得到错误消息时，就可以使用了

斯威夫特4

DispatchQueue.main.async { //code }

斯威夫特3

DispatchQueue.main.async(){ //code }

早期的Swift版本

dispatch_async(dispatch_get_main_queue()){ //code }

“这个应用程序正在从后台线程修改自动布局引擎”的主要问题是，它似乎在实际问题发生后很长一段时间才被记录下来，这可能会使它很难排除故障。

我设法通过创建三个符号断点来解决这个问题。

调试>断点>创建符号断点…

断点1:

符号:-[UIView setNeedsLayout] 条件:!(BOOL)[NSThread是主线程]

断点2:

符号:-[UIView layoutIfNeeded] 条件:!(BOOL)[NSThread是主线程]

断点3:

符号:-[UIView updateConstraintsIfNeeded] 条件:!(BOOL)[NSThread是主线程]

使用这些断点，您可以很容易地在非主线程上错误地调用UI方法的实际行中获得断点。

You already have the correct code answer from @Mark but, just to share my findings: The issue is that you are requesting a change in the view and assuming that it will happen instantly. In reality, the loading of a view depends on the available resources. If everything loads quickly enough and there are no delays then you don't notice anything. In scenarios, where there is any delay due to the process thread being busy etc, the application runs into a situation where it is supposed to display something even though its not ready yet. Hence, it is advisable to dispatch these requests in a asynchronous queues so, they get executed based on the load.

I also encountered this problem, seeing a ton of these messages and stack traces being printed in the output, when I resized the window to a smaller size than its initial value. Spending a long time figuring out the problem, I thought I'd share the rather simple solution. I had once enabled Can Draw Concurrently on an NSTextView through IB. That tells AppKit that it can call the view's draw(_:) method from another thread. After disabling it, I no longer got any error messages. I didn't experience any problems before updating to macOS 10.14 Beta, but at the same time, I also started modifying the code to perform work with the text view.