ios程序运行后，异步访问了一个网络请求。
然后在解析了从服务器返回的信息后，直接new了UIAlertView对象，准备弹窗提示，这时候控制台打印了一串异常的信息：
This application is modifying the autolayout engine from a background thread, which can lead to engine corruption and weird crashes. This will cause an exception in a future release.
下面还有一串好长的日志：
This application is modifying the autolayout engine from a background thread, which can lead to engine corruption and weird crashes. This will cause an exception in a future release. Stack:( 0 CoreFoundation 0x004eda84 __exceptionPreprocess + 180 1 libobjc.A.dylib 0x041d8e02 objc_exception_throw + 50 2 CoreFoundation 0x004ed9ad +[NSException raise:format:] + 141 3 Foundation 0x02b0974b _AssertAutolayoutOnMainThreadOnly + 96 4 Foundation 0x02931f49 -[NSISEngine withBehaviors:performModifications:] + 26 5 Foundation 0x029354a4 -[NSISEngine withAutomaticOptimizationDisabled:] + 48 6 UIKit 0x01256d98 -[UIView(UIConstraintBasedLayout) _calculatedSystemLayoutSizeFittingSize:withHorizontalFittingPriority:verticalFittingPriority:hasIntentionallyCollapsedHeight:] + 1194 7 UIKit 0x012587e9 -[UIView(AdditionalLayoutSupport) _systemLayoutSizeFittingSize:withHorizontalFittingPriority:verticalFittingPriority:hasIntentionallyCollapsedHeight:] + 972 8 UIKit 0x01258343 -[UIView(UIConstraintBasedLayout) systemLayoutSizeFittingSize:withHorizontalFittingPriority:verticalFittingPriority:] + 127 9 UIKit 0x0125838f -[UIView(UIConstraintBasedLayout) systemLayoutSizeFittingSize:] + 71 10 UIKit 0x0137b017 -[_UIAlertControllerView _minimumSizeForAllActions] + 589 11 UIKit 0x0137789b -[_UIAlertControllerView _itemSizeForHorizontalLayout:] + 451 12 UIKit 0x01377acf -[_UIAlertControllerView _canLayOutActionsHorizontally] + 108 13 UIKit 0x01377ff7 -[_UIAlertControllerView _actionLayoutDirectionChanged] + 42 14 UIKit 0x0137d13a -[_UIAlertControllerView _updateBackdrop] + 577 15 UIKit 0x0137bf85 -[_UIAlertControllerView _updateStyleForIdiomChange:] + 156 16 UIKit 0x0137beb1 -[_UIAlertControllerView _setVisualStyle:] + 296 17 UIKit 0x00bfebdd -[UIAlertController _updateProvidedStyleWithTraitCollection:] + 525 18 UIKit 0x00bfecd1 -[UIAlertController _updateProvidedStyle] + 68 19 UIKit 0x00bfee39 -[UIAlertController _resolvedStyleChanged] + 35 20 UIKit 0x00bfe30a -[UIAlertController viewDidLoad] + 98 21 UIKit 0x00a42a86 -[UIViewController _sendViewDidLoadWithAppearanceProxyObjectTaggingEnabled] + 44 22 UIKit 0x00a475a6 -[UIViewController loadViewIfRequired] + 1384 23 UIKit 0x00a479c5 -[UIViewController view] + 35 24 UIKit 0x00a63ba2 -[UIViewController _setPresentationController:] + 117 25 UIKit 0x00a5a1c6 -[UIViewController _presentViewController:modalSourceViewController:presentationController:animationController:interactionController:completion:] + 1503 26 UIKit 0x00a5c143 -[UIViewController _presentViewController:withAnimationController:completion:] + 5297 27 UIKit 0x00a5f34b __62-[UIViewController presentViewController:animated:completion:]_block_invoke + 397 28 UIKit 0x00a5f690 -[UIViewController _performCoordinatedPresentOrDismiss:animated:] + 493 29 UIKit 0x00a5f177 -[UIViewController presentViewController:animated:completion:] + 182 30 UIKit 0x013667ff -[_UIAlertControllerShimPresenterWindow presentAlertController:animated:completionBlock:] + 580 31 UIKit 0x01364912 -[_UIAlertControllerShimPresenter _presentAlertControllerAnimated:completion:] + 235 32 UIKit 0x00c11990 -[UIAlertView _showAnimated:] + 276 33 UIKit 0x00c11b76 -[UIAlertView show] + 41 34 心动爱 0x0012997a __37-[MainViewController checkAppVersion]_block_invoke + 762 35 CFNetwork 0x03692b62 __67+[NSURLConnection sendAsynchronousRequest:queue:completionHandler:]_block_invoke_2 + 177 36 Foundation 0x029e4a6b __NSBLOCKOPERATION_IS_CALLING_OUT_TO_A_BLOCK__ + 12 37 Foundation 0x029088ff -[NSBlockOperation main] + 108 38 Foundation 0x028e8d84 -[__NSOperationInternal _start:] + 697 39 Foundation 0x028e8ac4 -[NSOperation start] + 83 40 Foundation 0x028e8902 __NSOQSchedule_f + 245 41 libdispatch.dylib 0x04a2f9cd _dispatch_client_callout + 14 42 libdispatch.dylib 0x04a13650 _dispatch_queue_drain + 2227 43 libdispatch.dylib 0x04a12b04 _dispatch_queue_invoke + 570 44 libdispatch.dylib 0x04a157bb _dispatch_root_queue_drain + 550 45 libdispatch.dylib 0x04a1558e _dispatch_worker_thread3 + 115 46 libsystem_pthread.dylib 0x04d4f270 _pthread_wqthread + 1050 47 libsystem_pthread.dylib 0x04d4cf82 start_wqthread + 34 ) This application is modifying the autolayout engine from a background thread, which can lead to engine corruption and weird crashes. This will cause an exception in a future release. Stack:( 0 CoreFoundation 0x004eda84 __exceptionPreprocess + 180 1 libobjc.A.dylib 0x041d8e02 objc_exception_throw + 50 2 CoreFoundation 0x004ed9ad +[NSException raise:format:] + 141 3 Foundation 0x02b0974b _AssertAutolayoutOnMainThreadOnly + 96 4 Foundation 0x02931561 -[NSISEngine optimize] + 67 5 Foundation 0x02932024 -[NSISEngine withBehaviors:performModifications:] + 245 6 Foundation 0x029354a4 -[NSISEngine withAutomaticOptimizationDisabled:] + 48 7 UIKit 0x01256d98 -[UIView(UIConstraintBasedLayout) _calculatedSystemLayoutSizeFittingSize:withHorizontalFittingPriority:verticalFittingPriority:hasIntentionallyCollapsedHeight:] + 1194 8 UIKit 0x012587e9 -[UIView(AdditionalLayoutSupport) _systemLayoutSizeFittingSize:withHorizontalFittingPriority:verticalFittingPriority:hasIntentionallyCollapsedHeight:] + 972 9 UIKit 0x01258343 -[UIView(UIConstraintBasedLayout) systemLayoutSizeFittingSize:withHorizontalFittingPriority:verticalFittingPriority:] + 127 10 UIKit 0x0125838f -[UIView(UIConstraintBasedLayout) systemLayoutSizeFittingSize:] + 71 11 UIKit 0x0137b017 -[_UIAlertControllerView _minimumSizeForAllActions] + 589 12 UIKit 0x0137789b -[_UIAlertControllerView _itemSizeForHorizontalLayout:] + 451 13 UIKit 0x01377acf -[_UIAlertControllerView _canLayOutActionsHorizontally] + 108 14 UIKit 0x01377ff7 -[_UIAlertControllerView _actionLayoutDirectionChanged] + 42 15 UIKit 0x0137d13a -[_UIAlertControllerView _updateBackdrop] + 577 16 UIKit 0x0137bf85 -[_UIAlertControllerView _updateStyleForIdiomChange:] + 156 17 UIKit 0x0137beb1 -[_UIAlertControllerView _setVisualStyle:] + 296 18 UIKit 0x00bfebdd -[UIAlertController _updateProvidedStyleWithTraitCollection:] + 525 19 UIKit 0x00bfecd1 -[UIAlertController _updateProvidedStyle] + 68 20 UIKit 0x00bfee39 -[UIAlertController _resolvedStyleChanged] + 35 21 UIKit 0x00bfe30a -[UIAlertController viewDidLoad] + 98 22 UIKit 0x00a42a86 -[UIViewController _sendViewDidLoadWithAppearanceProxyObjectTaggingEnabled] + 44 23 UIKit 0x00a475a6 -[UIViewController loadViewIfRequired] + 1384 24 UIKit 0x00a479c5 -[UIViewController view] + 35 25 UIKit 0x00a63ba2 -[UIViewController _setPresentationController:] + 117 26 UIKit 0x00a5a1c6 -[UIViewController _presentViewController:modalSourceViewController:presentationController:animationController:interactionController:completion:] + 1503 27 UIKit 0x00a5c143 -[UIViewController _presentViewController:withAnimationController:completion:] + 5297 28 UIKit 0x00a5f34b __62-[UIViewController presentViewController:animated:completion:]_block_invoke + 397 29 UIKit 0x00a5f690 -[UIViewController _performCoordinatedPresentOrDismiss:animated:] + 493 30 UIKit 0x00a5f177 -[UIViewController presentViewController:animated:completion:] + 182 31 UIKit 0x013667ff -[_UIAlertControllerShimPresenterWindow presentAlertController:animated:completionBlock:] + 580 32 UIKit 0x01364912 -[_UIAlertControllerShimPresenter _presentAlertControllerAnimated:completion:] + 235 33 UIKit 0x00c11990 -[UIAlertView _showAnimated:] + 276 34 UIKit 0x00c11b76 -[UIAlertView show] + 41 35 心动爱 0x0012997a __37-[MainViewController checkAppVersion]_block_invoke + 762 36 CFNetwork 0x03692b62 __67+[NSURLConnection sendAsynchronousRequest:queue:completionHandler:]_block_invoke_2 + 177 37 Foundation 0x029e4a6b __NSBLOCKOPERATION_IS_CALLING_OUT_TO_A_BLOCK__ + 12 38 Foundation 0x029088ff -[NSBlockOperation main] + 108 39 Foundation 0x028e8d84 -[__NSOperationInternal _start:] + 697 40 Foundation 0x028e8ac4 -[NSOperation start] + 83 41 Foundation 0x028e8902 __NSOQSchedule_f + 245 42 libdispatch.dylib 0x04a2f9cd _dispatch_client_callout + 14 43 libdispatch.dylib 0x04a13650 _dispatch_queue_drain + 2227 44 libdispatch.dylib 0x04a12b04 _dispatch_queue_invoke + 570 45 libdispatch.dylib 0x04a157bb _dispatch_root_queue_drain + 550 46 libdispatch.dylib 0x04a1558e _dispatch_worker_thread3 + 115 47 libsystem_pthread.dylib 0x04d4f270 _pthread_wqthread + 1050 48 libsystem_pthread.dylib 0x04d4cf82 start_wqthread + 34 )
什么意思呢？翻译过来大概是指说在一个异步线程修改了应用程序的布局，将会引起崩溃异常。。。。
然后反省了一下，记起以前师傅说过的话：耗时操作放在异步线程上，更新UI要放在主线程上。
我这里出现这个原因应该是：我在异步访问了一个网络请求后，解析从服务器返回的信息，然后马上就new了一个UIAlertView对象，准备弹窗提示，
这相当于在一个异步线程里面对UI进行了更新，所以导致出现了异常警告。
正确的作法是，异步访问了网络请求后， 如果想new个UIAlertView进行弹窗提示，应该去主线程进行。。。这样就OK了