执行后台获取完成处理程序后应用程序崩溃 [英] App Crashes after executing background fetch completionHandler

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本文介绍了执行后台获取完成处理程序后应用程序崩溃的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

我已经为 iOS 7 更新了我们的应用程序并添加了后台获取功能.但是，由于此功能，我注意到一些崩溃.后台获取调用完成后，完成处理程序块将使用新数据/无数据执行.这会导致调用我的自定义导航 NavigationBar 的layoutSubviews"，有时应用程序会因以下堆栈跟踪而崩溃.我自己无法重现这个问题，但不断从我们的用户那里收到这些崩溃日志.任何帮助将不胜感激.

线程 0 崩溃:0 libsystem_platform.dylib 0x39cba486 _platform_memmove$VARIANT$Swift + 1021 基础 0x2fce8f47 -[NSData(NSData) getBytes:range:] + 4192 核心基金会 0x2f30637d CFDataGetBytes + 2053 ImageIO 0x300e7357 CGImageReadGetBytesAtOffset + 2834 ImageIO 0x300e7231 CGImageReadSessionGetBytes + 295 ImageIO 0x3022baeb read_fn + 236 ImageIO 0x300e7189 png_read_sig + 457 ImageIO 0x300e6e0d _cg_png_read_info + 338 ImageIO 0x300ef62f copyImageBlockSetPNG + 11239 ImageIO 0x300eec4b ImageProviderCopyImageBlockSetCallback + 53910 CoreGraphics 0x2f43577d CGImageProviderCopyImageBlockSetWithOptions + 13711 CoreGraphics 0x2f43a145 subImageProviderCopyImageBlockSet + 30512 CoreGraphics 0x2f43577d CGImageProviderCopyImageBlockSetWithOptions + 13713 核心图形 0x2f435433 img_blocks_create + 38314 CoreGraphics 0x2f4286fd img_data_lock + 105315 CoreGraphics 0x2f427ae1 CGSImageDataLock + 8916 libRIP.A.dylib 0x2f774da7 ripc_AcquireImage + 9917 libRIP.A.dylib 0x2f774131 ripc_DrawImage + 60118 CoreGraphics 0x2f4279f3 CGContextDelegateDrawImage + 5119 CoreGraphics 0x2f427879 CGContextDrawImage + 28520 WebCore 0x373120db WebCore::GraphicsContext::drawNativeImage(CGImage*, WebCore::FloatSize const&, WebCore::ColorSpace, WebCore::FloatRect const&, WebCore::FloatRect const&, float, WebCore::CompositeOperator, WebCore::BlendMode、WebCore::ImageOrientation) + 112721 WebCore 0x37310e79 WebCore::BitmapImage::draw(WebCore::GraphicsContext*, WebCore::FloatRect const&, WebCore::FloatRect const&, WebCore::ColorSpace, WebCore::CompositeOperator, WebCore::BlendMode, WebCore::RespectImageOrientationEnum) + 34922 WebCore 0x3735d897 WebCore::BitmapImage::draw(WebCore::GraphicsContext*, WebCore::FloatRect const&, WebCore::FloatRect const&, WebCore::ColorSpace, WebCore::CompositeOperator, WebCore::BlendMode) + 3123 WebCore 0x3735892f WebCore::Image::drawTiled(WebCore::GraphicsContext*, WebCore::FloatRect const&, WebCore::FloatPoint const&, WebCore::FloatSize const&, WebCore::ColorSpace, WebCore::CompositeOperator, WebCore::混合模式) + 49924 WebCore 0x37358735 WebCore::GraphicsContext::drawTiledImage(WebCore::Image*, WebCore::ColorSpace, WebCore::IntRect const&, WebCore::IntPoint const&, WebCore::IntSize const&, WebCore::CompositeOperator, bool,网络核心::混合模式) + 19325 WebCore 0x3728bc11 WebCore::RenderBoxModelObject::paintFillLayerExtended(WebCore::PaintInfo const&, WebCore::Color const&, WebCore::FillLayer const*, WebCore::LayoutRect const&, WebCore::BackgroundBleedAvoidance, WebCore::InlineFlowBox*,WebCore::LayoutSize const&、WebCore::CompositeOperator、WebCore::RenderObject*) + 332126 WebCore 0x3728addd WebCore::RenderBox::paintFillLayers(WebCore::PaintInfo const&, WebCore::Color const&, WebCore::FillLayer const*, WebCore::LayoutRect const&, WebCore::BackgroundBleedAvoidance, WebCore::CompositeOperator, WebCore::渲染对象*) + 44927 WebCore 0x3728ab41 WebCore::RenderBox::paintBackground(WebCore::PaintInfo const&, WebCore::LayoutRect const&, WebCore::BackgroundBleedAvoidance) + 31728 WebCore 0x37289ee5 WebCore::RenderBox::paintBoxDecorations(WebCore::PaintInfo&, WebCore::LayoutPoint const&) + 32929 WebCore 0x3728806f WebCore::RenderBlock::paintObject(WebCore::PaintInfo&, WebCore::LayoutPoint const&) + 5530 WebCore 0x37289c3f WebCore::RenderBlock::paint(WebCore::PaintInfo&, WebCore::LayoutPoint const&) + 18731 WebCore 0x37288cc9 WebCore::RenderBlock::paintFloats(WebCore::PaintInfo&, WebCore::LayoutPoint const&, bool) + 30532 WebCore 0x3728813d WebCore::RenderBlock::paintObject(WebCore::PaintInfo&, WebCore::LayoutPoint const&) + 26133 WebCore 0x37289c3f WebCore::RenderBlock::paint(WebCore::PaintInfo&, WebCore::LayoutPoint const&) + 18734 WebCore 0x37288cfb WebCore::RenderBlock::paintFloats(WebCore::PaintInfo&, WebCore::LayoutPoint const&, bool) + 35535 WebCore 0x3728813d WebCore::RenderBlock::paintObject(WebCore::PaintInfo&, WebCore::LayoutPoint const&) + 26136 WebCore 0x37289c3f WebCore::RenderBlock::paint(WebCore::PaintInfo&, WebCore::LayoutPoint const&) + 18737 WebCore 0x37288861 WebCore::RenderLayer::paintForegroundForFragmentsWithPhase(WebCore::PaintPhase，WTF::Vector<WebCore::LayerFragment，1ul，WTF::CrashOnOverflow>const&，WebCore::GraphicsContext*，WebCore::RenderLayer::constLayer;, unsigned int, WebCore::RenderObject*) + 26938 WebCore 0x372886e7 WebCore::RenderLayer::paintForegroundForFragments(WTF::Vector<WebCore::LayerFragment, 1ul, WTF::CrashOnOverflow> const&, WebCore::GraphicsContext*, WebCore::GraphicsContext*, WebCore::LayoutRect const&,bool, WebCore::RenderLayer::LayerPaintingInfo const&, unsigned int, WebCore::RenderObject*, bool, bool) + 23539 WebCore 0x37286435 WebCore::RenderLayer::paintLayerContents(WebCore::GraphicsContext*, WebCore::RenderLayer::LayerPaintingInfo const&, unsigned int) + 158540 WebCore 0x37285ca9 WebCore::RenderLayer::paintLayer(WebCore::GraphicsContext*, WebCore::RenderLayer::LayerPaintingInfo const&, unsigned int) + 62141 WebCore 0x372885d9 WebCore::RenderLayer::paintList(WTF::Vector<WebCore::RenderLayer*, 0ul, WTF::CrashOnOverflow>*, WebCore::GraphicsContext*, WebCore::RenderLayer::LayerPaintingInfo const&, unsigned int)+ 10142 WebCore 0x3728647f WebCore::RenderLayer::paintLayerContents(WebCore::GraphicsContext*, WebCore::RenderLayer::LayerPaintingInfo const&, unsigned int) + 165943 WebCore 0x37285ca9 WebCore::RenderLayer::paintLayer(WebCore::GraphicsContext*, WebCore::RenderLayer::LayerPaintingInfo const&, unsigned int) + 62144 WebCore 0x372885d9 WebCore::RenderLayer::paintList(WTF::Vector<WebCore::RenderLayer*, 0ul, WTF::CrashOnOverflow>*, WebCore::GraphicsContext*, WebCore::RenderLayer::LayerPaintingInfo const&, unsigned int)+ 10145 WebCore 0x3728647f WebCore::RenderLayer::paintLayerContents(WebCore::GraphicsContext*, WebCore::RenderLayer::LayerPaintingInfo const&, unsigned int) + 165946 WebCore 0x37285ca9 WebCore::RenderLayer::paintLayer(WebCore::GraphicsContext*, WebCore::RenderLayer::LayerPaintingInfo const&, unsigned int) + 62147 WebCore 0x372859b3 WebCore::RenderLayer::paint(WebCore::GraphicsContext*, WebCore::LayoutRect const&, unsigned int, WebCore::RenderObject*, WebCore::RenderRegion*, unsigned int) + 10348 WebCore 0x3728541b WebCore::FrameView::paintContents(WebCore::GraphicsContext*, WebCore::IntRect const&) + 49949 WebKit 0x37c4578d -[WebFrame(WebInternal)_drawRect:contentsOnly:] + 35750 WebKit 0x37c455b9 -[WebHTMLView drawSingleRect:] + 13751 WebKit 0x37c454db -[WebHTMLView drawRect:] + 4352 WebCore 0x37284d93 -[WAKView _drawRect:context:lockFocus:] + 27553 WebCore 0x37284ec7 -[WAKView _drawRect:context:lockFocus:] + 58354 WebCore 0x37284ec7 -[WAKView _drawRect:context:lockFocus:] + 58355 WebCore 0x37284ec7 -[WAKView _drawRect:context:lockFocus:] + 58356 WebCore 0x37284ec7 -[WAKView _drawRect:context:lockFocus:] + 58357 WebCore 0x37284c47 -[WAKView displayRect:] + 5958 WebCore 0x37284c03 -[WAKWindow displayRect:] + 5559 WebCore 0x37284b49 WebCore::TileCache::drawWindowContent(TileLayer*, CGContext*, CGRect) + 67360 WebCore 0x37284525 WebCore::TileCache::drawLayer(TileLayer*, CGContext*) + 50561 QuartzCore 0x317d3813 CABackingStoreUpdate_ + 185962 QuartzCore 0x318ad735 ___ZN2CA5Layer8display_Ev_block_invoke + 5363 QuartzCore 0x317d30c3 x_blame_allocations + 8364 QuartzCore 0x317d2d77 CA::Layer::display_() + 111965 QuartzCore 0x317b6969 CA::Layer::display_if_needed(CA::Transaction*) + 20966 QuartzCore 0x317b6601 CA::Layer::layout_and_display_if_needed(CA::Transaction*) + 2567 QuartzCore 0x317b600d CA::Context::commit_transaction(CA::Transaction*) + 22968 QuartzCore 0x317b5e1f CA::Transaction::commit() + 31569 UIKit 0x31d973c9 _UIWindowUpdateVisibleContextOrder + 20970 UIKit 0x31d9729d +[UIWindow _prepareWindowsPassingTestForAppResume:] + 1371 UIKit 0x31db0ac5 -[UIApplication _updateSnapshotAndStateRestorationArchiveForBackgroundEvent:saveState:exitIfCouldNotRestoreState:] + 20172 UIKit 0x31db0d81 -[UIApplication _replyToBackgroundFetchRequestWithResult:remoteNotificationToken:sequenceNumber:updateApplicationSnapshot:] + 10573 UIKit 0x31db138d __61-[UIApplication _handleOpportunisticFetchWithSequenceNumber:]_block_invoke + 3774 MyApp 0x001456b7 -[获取列表:错误:withBackgroundFetchCompletionHandler:](List.m:421)75 MyApp 0x00144f87 __71-[List fetchFromServerWithBackgroundFetchCompletionHandler:]_block_invoke (List.m:292)76 MyApp 0x0021ed07 APICompletionBlock_block_invoke_6 (APIRequest.m:305)77 libdispatch.dylib 0x39b8c103 _dispatch_call_block_and_release + 1178 libdispatch.dylib 0x39b8c0ef _dispatch_client_callout + 2379 libdispatch.dylib 0x39b8e9a9 _dispatch_main_queue_callback_4CF + 26980 核心基金会 0x2f3785b9 __CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__ + 981 核心基金会 0x2f376e85 __CFRunLoopRun + 130982 核心基金会 0x2f2e1541 CFRunLoopRunSpecific + 52583 核心基金会 0x2f2e1323 CFRunLoopRunInMode + 10784 图形服务 0x340182eb GSEventRunModal + 13985 UIKit 0x31b981e5 UIApplicationMain + 113786 我的应用程序 0x0009f77f 主 (main.m:14)

解决方案

当您将应用程序置于后台时，它会将当前视图的快照保存到内存中，以便在您双击主页按钮时显示.使用iOS7后台刷新功能((void)application:(UIApplication *)application didReceiveRemoteNotification:(NSDictionary *)userInfo fetchCompletionHandler:(void (^)(UIBackgroundFetchResult result))completionHandler)，你必须执行completionHandler 执行完获取请求后的函数.

该函数的执行还会触发 UI 的更新 - [UIApplication _updateSnapshotAndStateRestorationArchiveForBackgroundEvent:saveState:exitIfCouldNotRestoreState:]，在您的情况下，它会触发从 背景计算 UIWebView 的框架线程.UIWebView 只能从 UIThread 更新，所以为了克服这个崩溃，我建议将 completionHandler 包装在主线程上执行:

<前>- (void)application:(UIApplication *)application didReceiveRemoteNotification:(NSDictionary *)userInfo fetchCompletionHandler:(void (^)(UIBackgroundFetchResult result))completionHandler{void (^safeHandler)(UIBackgroundFetchResult) = ^(UIBackgroundFetchResult 结果){dispatch_async(dispatch_get_main_queue(),^{完成处理程序(结果)；});};[someInstance doSomethingInBackground:userInfo withHandler:safeHandler];}

而且您将不再需要担心从哪里调用 completionHandler(现在是 safeHandler).

I have updated our app for iOS 7 and added the background fetch functionality. However, i'm noticing some crashes because of this feature. After background fetch call is completed, the completion handler block is executed with either new/no data. This results in a call to 'layoutSubviews' of my custom navigation NavigationBar and sometimes app is crashing with the following stack trace. I could not reproduce this issue myself but constantly receiving these crash logs from our users. Any help would be appreciated.

Thread 0 Crashed:
0   libsystem_platform.dylib            0x39cba486 _platform_memmove$VARIANT$Swift + 102
1   Foundation                          0x2fce8f47 -[NSData(NSData) getBytes:range:] + 419
2   CoreFoundation                      0x2f30637d CFDataGetBytes + 205
3   ImageIO                             0x300e7357 CGImageReadGetBytesAtOffset + 283
4   ImageIO                             0x300e7231 CGImageReadSessionGetBytes + 29
5   ImageIO                             0x3022baeb read_fn + 23
6   ImageIO                             0x300e7189 png_read_sig + 45
7   ImageIO                             0x300e6e0d _cg_png_read_info + 33
8   ImageIO                             0x300ef62f copyImageBlockSetPNG + 1123
9   ImageIO                             0x300eec4b ImageProviderCopyImageBlockSetCallback + 539
10  CoreGraphics                        0x2f43577d CGImageProviderCopyImageBlockSetWithOptions + 137
11  CoreGraphics                        0x2f43a145 subImageProviderCopyImageBlockSet + 305
12  CoreGraphics                        0x2f43577d CGImageProviderCopyImageBlockSetWithOptions + 137
13  CoreGraphics                        0x2f435433 img_blocks_create + 383
14  CoreGraphics                        0x2f4286fd img_data_lock + 1053
15  CoreGraphics                        0x2f427ae1 CGSImageDataLock + 89
16  libRIP.A.dylib                      0x2f774da7 ripc_AcquireImage + 99
17  libRIP.A.dylib                      0x2f774131 ripc_DrawImage + 601
18  CoreGraphics                        0x2f4279f3 CGContextDelegateDrawImage + 51
19  CoreGraphics                        0x2f427879 CGContextDrawImage + 285
20  WebCore                             0x373120db WebCore::GraphicsContext::drawNativeImage(CGImage*, WebCore::FloatSize const&, WebCore::ColorSpace, WebCore::FloatRect const&, WebCore::FloatRect const&, float, WebCore::CompositeOperator, WebCore::BlendMode, WebCore::ImageOrientation) + 1127
21  WebCore                             0x37310e79 WebCore::BitmapImage::draw(WebCore::GraphicsContext*, WebCore::FloatRect const&, WebCore::FloatRect const&, WebCore::ColorSpace, WebCore::CompositeOperator, WebCore::BlendMode, WebCore::RespectImageOrientationEnum) + 349
22  WebCore                             0x3735d897 WebCore::BitmapImage::draw(WebCore::GraphicsContext*, WebCore::FloatRect const&, WebCore::FloatRect const&, WebCore::ColorSpace, WebCore::CompositeOperator, WebCore::BlendMode) + 31
23  WebCore                             0x3735892f WebCore::Image::drawTiled(WebCore::GraphicsContext*, WebCore::FloatRect const&, WebCore::FloatPoint const&, WebCore::FloatSize const&, WebCore::ColorSpace, WebCore::CompositeOperator, WebCore::BlendMode) + 499
24  WebCore                             0x37358735 WebCore::GraphicsContext::drawTiledImage(WebCore::Image*, WebCore::ColorSpace, WebCore::IntRect const&, WebCore::IntPoint const&, WebCore::IntSize const&, WebCore::CompositeOperator, bool, WebCore::BlendMode) + 193
25  WebCore                             0x3728bc11 WebCore::RenderBoxModelObject::paintFillLayerExtended(WebCore::PaintInfo const&, WebCore::Color const&, WebCore::FillLayer const*, WebCore::LayoutRect const&, WebCore::BackgroundBleedAvoidance, WebCore::InlineFlowBox*, WebCore::LayoutSize const&, WebCore::CompositeOperator, WebCore::RenderObject*) + 3321
26  WebCore                             0x3728addd WebCore::RenderBox::paintFillLayers(WebCore::PaintInfo const&, WebCore::Color const&, WebCore::FillLayer const*, WebCore::LayoutRect const&, WebCore::BackgroundBleedAvoidance, WebCore::CompositeOperator, WebCore::RenderObject*) + 449
27  WebCore                             0x3728ab41 WebCore::RenderBox::paintBackground(WebCore::PaintInfo const&, WebCore::LayoutRect const&, WebCore::BackgroundBleedAvoidance) + 317
28  WebCore                             0x37289ee5 WebCore::RenderBox::paintBoxDecorations(WebCore::PaintInfo&, WebCore::LayoutPoint const&) + 329
29  WebCore                             0x3728806f WebCore::RenderBlock::paintObject(WebCore::PaintInfo&, WebCore::LayoutPoint const&) + 55
30  WebCore                             0x37289c3f WebCore::RenderBlock::paint(WebCore::PaintInfo&, WebCore::LayoutPoint const&) + 187
31  WebCore                             0x37288cc9 WebCore::RenderBlock::paintFloats(WebCore::PaintInfo&, WebCore::LayoutPoint const&, bool) + 305
32  WebCore                             0x3728813d WebCore::RenderBlock::paintObject(WebCore::PaintInfo&, WebCore::LayoutPoint const&) + 261
33  WebCore                             0x37289c3f WebCore::RenderBlock::paint(WebCore::PaintInfo&, WebCore::LayoutPoint const&) + 187
34  WebCore                             0x37288cfb WebCore::RenderBlock::paintFloats(WebCore::PaintInfo&, WebCore::LayoutPoint const&, bool) + 355
35  WebCore                             0x3728813d WebCore::RenderBlock::paintObject(WebCore::PaintInfo&, WebCore::LayoutPoint const&) + 261
36  WebCore                             0x37289c3f WebCore::RenderBlock::paint(WebCore::PaintInfo&, WebCore::LayoutPoint const&) + 187
37  WebCore                             0x37288861 WebCore::RenderLayer::paintForegroundForFragmentsWithPhase(WebCore::PaintPhase, WTF::Vector<WebCore::LayerFragment, 1ul, WTF::CrashOnOverflow> const&, WebCore::GraphicsContext*, WebCore::RenderLayer::LayerPaintingInfo const&, unsigned int, WebCore::RenderObject*) + 269
38  WebCore                             0x372886e7 WebCore::RenderLayer::paintForegroundForFragments(WTF::Vector<WebCore::LayerFragment, 1ul, WTF::CrashOnOverflow> const&, WebCore::GraphicsContext*, WebCore::GraphicsContext*, WebCore::LayoutRect const&, bool, WebCore::RenderLayer::LayerPaintingInfo const&, unsigned int, WebCore::RenderObject*, bool, bool) + 235
39  WebCore                             0x37286435 WebCore::RenderLayer::paintLayerContents(WebCore::GraphicsContext*, WebCore::RenderLayer::LayerPaintingInfo const&, unsigned int) + 1585
40  WebCore                             0x37285ca9 WebCore::RenderLayer::paintLayer(WebCore::GraphicsContext*, WebCore::RenderLayer::LayerPaintingInfo const&, unsigned int) + 621
41  WebCore                             0x372885d9 WebCore::RenderLayer::paintList(WTF::Vector<WebCore::RenderLayer*, 0ul, WTF::CrashOnOverflow>*, WebCore::GraphicsContext*, WebCore::RenderLayer::LayerPaintingInfo const&, unsigned int) + 101
42  WebCore                             0x3728647f WebCore::RenderLayer::paintLayerContents(WebCore::GraphicsContext*, WebCore::RenderLayer::LayerPaintingInfo const&, unsigned int) + 1659
43  WebCore                             0x37285ca9 WebCore::RenderLayer::paintLayer(WebCore::GraphicsContext*, WebCore::RenderLayer::LayerPaintingInfo const&, unsigned int) + 621
44  WebCore                             0x372885d9 WebCore::RenderLayer::paintList(WTF::Vector<WebCore::RenderLayer*, 0ul, WTF::CrashOnOverflow>*, WebCore::GraphicsContext*, WebCore::RenderLayer::LayerPaintingInfo const&, unsigned int) + 101
45  WebCore                             0x3728647f WebCore::RenderLayer::paintLayerContents(WebCore::GraphicsContext*, WebCore::RenderLayer::LayerPaintingInfo const&, unsigned int) + 1659
46  WebCore                             0x37285ca9 WebCore::RenderLayer::paintLayer(WebCore::GraphicsContext*, WebCore::RenderLayer::LayerPaintingInfo const&, unsigned int) + 621
47  WebCore                             0x372859b3 WebCore::RenderLayer::paint(WebCore::GraphicsContext*, WebCore::LayoutRect const&, unsigned int, WebCore::RenderObject*, WebCore::RenderRegion*, unsigned int) + 103
48  WebCore                             0x3728541b WebCore::FrameView::paintContents(WebCore::GraphicsContext*, WebCore::IntRect const&) + 499
49  WebKit                              0x37c4578d -[WebFrame(WebInternal) _drawRect:contentsOnly:] + 357
50  WebKit                              0x37c455b9 -[WebHTMLView drawSingleRect:] + 137
51  WebKit                              0x37c454db -[WebHTMLView drawRect:] + 43
52  WebCore                             0x37284d93 -[WAKView _drawRect:context:lockFocus:] + 275
53  WebCore                             0x37284ec7 -[WAKView _drawRect:context:lockFocus:] + 583
54  WebCore                             0x37284ec7 -[WAKView _drawRect:context:lockFocus:] + 583
55  WebCore                             0x37284ec7 -[WAKView _drawRect:context:lockFocus:] + 583
56  WebCore                             0x37284ec7 -[WAKView _drawRect:context:lockFocus:] + 583
57  WebCore                             0x37284c47 -[WAKView displayRect:] + 59
58  WebCore                             0x37284c03 -[WAKWindow displayRect:] + 55
59  WebCore                             0x37284b49 WebCore::TileCache::drawWindowContent(TileLayer*, CGContext*, CGRect) + 673
60  WebCore                             0x37284525 WebCore::TileCache::drawLayer(TileLayer*, CGContext*) + 505
61  QuartzCore                          0x317d3813 CABackingStoreUpdate_ + 1859
62  QuartzCore                          0x318ad735 ___ZN2CA5Layer8display_Ev_block_invoke + 53
63  QuartzCore                          0x317d30c3 x_blame_allocations + 83
64  QuartzCore                          0x317d2d77 CA::Layer::display_() + 1119
65  QuartzCore                          0x317b6969 CA::Layer::display_if_needed(CA::Transaction*) + 209
66  QuartzCore                          0x317b6601 CA::Layer::layout_and_display_if_needed(CA::Transaction*) + 25
67  QuartzCore                          0x317b600d CA::Context::commit_transaction(CA::Transaction*) + 229
68  QuartzCore                          0x317b5e1f CA::Transaction::commit() + 315
69  UIKit                               0x31d973c9 _UIWindowUpdateVisibleContextOrder + 209
70  UIKit                               0x31d9729d +[UIWindow _prepareWindowsPassingTestForAppResume:] + 13
71  UIKit                               0x31db0ac5 -[UIApplication _updateSnapshotAndStateRestorationArchiveForBackgroundEvent:saveState:exitIfCouldNotRestoreState:] + 201
72  UIKit                               0x31db0d81 -[UIApplication _replyToBackgroundFetchRequestWithResult:remoteNotificationToken:sequenceNumber:updateApplicationSnapshot:] + 105
73  UIKit                               0x31db138d __61-[UIApplication _handleOpportunisticFetchWithSequenceNumber:]_block_invoke + 37
74  MyApp                               0x001456b7 -[List fetched:error:withBackgroundFetchCompletionHandler:] (List.m:421)
75  MyApp                               0x00144f87 __71-[List fetchFromServerWithBackgroundFetchCompletionHandler:]_block_invoke (List.m:292)
76  MyApp                               0x0021ed07 APICompletionBlock_block_invoke_6 (APIRequest.m:305)
77  libdispatch.dylib                   0x39b8c103 _dispatch_call_block_and_release + 11
78  libdispatch.dylib                   0x39b8c0ef _dispatch_client_callout + 23
79  libdispatch.dylib                   0x39b8e9a9 _dispatch_main_queue_callback_4CF + 269
80  CoreFoundation                      0x2f3785b9 __CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__ + 9
81  CoreFoundation                      0x2f376e85 __CFRunLoopRun + 1309
82  CoreFoundation                      0x2f2e1541 CFRunLoopRunSpecific + 525
83  CoreFoundation                      0x2f2e1323 CFRunLoopRunInMode + 107
84  GraphicsServices                    0x340182eb GSEventRunModal + 139
85  UIKit                               0x31b981e5 UIApplicationMain + 1137
86  MyApp                               0x0009f77f main (main.m:14)

解决方案

When you leave your app to the background, it saves the snapshot of the current view to the memory so it could be shown when you double-click the home button. With the iOS7 background refresh feature ((void)application:(UIApplication *)application didReceiveRemoteNotification:(NSDictionary *)userInfo fetchCompletionHandler:(void (^)(UIBackgroundFetchResult result))completionHandler), you must execute the completionHandler function after you finish executing your fetch request.

The execution of that function also triggers updates to the UI - [UIApplication _updateSnapshotAndStateRestorationArchiveForBackgroundEvent:saveState:exitIfCouldNotRestoreState:], and in your case it triggers calculating the frame for a UIWebView from a background thread. UIWebView can be updated only from the UIThread, so to overcome this crash I would suggest to wrap the completionHandler with execution on the main thread:

- (void)application:(UIApplication *)application didReceiveRemoteNotification:(NSDictionary *)userInfo fetchCompletionHandler:(void (^)(UIBackgroundFetchResult result))completionHandler
{
    void (^safeHandler)(UIBackgroundFetchResult) = ^(UIBackgroundFetchResult result){
        dispatch_async(dispatch_get_main_queue(), ^{
            completionHandler(result);
        });
    };
    [someInstance doSomethingInBackground:userInfo withHandler:safeHandler];
}

And you will no longer have to worry where you invoke the completionHandler (now safeHandler) from.

这篇关于执行后台获取完成处理程序后应用程序崩溃的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！

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