iOS 13 报错:[Assert] Unsupported use of UIKit view-customization API off the main thread

萤石摄像头回看，在iOS 11上运行好好，在iOS 13上却报错了，报错如下：

2021-05-11 15:36:38.174462+0800 App-Beta[1141:430280] [Assert] Unsupported use of UIKit view-customization API off the main thread. -setBackgroundColor: sent to <UIPickerTableView: 0x105ab2800; frame = (31 -37.6667; 103 291); clipsToBounds = YES; gestureRecognizers = <NSArray: 0x2811fc4b0>; layer = <CALayer: 0x281e0ed60>; contentOffset: {0, 0}; contentSize: {0, 0}; adjustedContentInset: {0, 0, 291, 0}; dataSource: (null)>
2021-05-11 15:36:38.175889+0800 App-Beta[1141:430280] [Assert] Unsupported use of UIKit view-customization API off the main thread. -_setBackgroundEffects: sent to <UIPickerTableView: 0x105ab2800; frame = (31 -37.6667; 103 291); clipsToBounds = YES; gestureRecognizers = <NSArray: 0x2811fc4b0>; layer = <CALayer: 0x281e0ed60>; contentOffset: {0, 0}; contentSize: {0, 0}; adjustedContentInset: {0, 0, 291, 0}; dataSource: (null)>
2021-05-11 15:36:38.176338+0800 App-Beta[1141:430280] [Assert] Unsupported use of UIKit view-customization API off the main thread. -setSeparatorColor: sent to <UIPickerTableView: 0x105ab2800; frame = (31 -37.6667; 103 291); clipsToBounds = YES; gestureRecognizers = <NSArray: 0x2811fc4b0>; layer = <CALayer: 0x281e0ed60>; contentOffset: {0, 0}; contentSize: {0, 0}; adjustedContentInset: {0, 0, 291, 0}; dataSource: (null)>
2021-05-11 15:36:38.177102+0800 App-Beta[1141:430280] [Assert] Unsupported use of UIKit view-customization API off the main thread. -setSeparatorStyle: sent to <UIPickerTableView: 0x105ab2800; frame = (31 -37.6667; 103 291); clipsToBounds = YES; gestureRecognizers = <NSArray: 0x2811fc4b0>; layer = <CALayer: 0x281e0ed60>; contentOffset: {0, 0}; contentSize: {0, 0}; adjustedContentInset: {0, 0, 291, 0}; dataSource: (null)>
...
2021-05-11 15:36:38.257101+0800 App-Beta[1141:430280] *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Modifications to the layout engine must not be performed from a background thread after it has been accessed from the main thread.'
...

从上面的报错可以看出是由于更新UI不在主线程中导致的。
解决方法也很简单，即把报错的代码放到主队列中执行：

• Modern Swift:

DispatchQueue.main.async {
// Update UI
}

• Older versions of Swift, pre Swift 3.

dispatch_async(dispatch_get_main_queue(){
// code here
})

• Objective-C:

dispatch_async(dispatch_get_main_queue(), ^{
// code here
});

参考：Getting a “This application is modifying the autolayout engine from a background thread” error?

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