UIWebDocumentView _updateSubviewCaches在iOS10中崩溃

Question

我在iOS10中更加严重地在HockeyApp中发生以下崩溃。请找到下面给出的崩溃日志。

主题4毁损：

0 libobjc.A.dylib 0x0000000187242f30 objc_msgSend + 16 
1 UIKit 0x000000018e86e914 -[UIWebDocumentView _updateSubviewCaches] + 36 
2 UIKit 0x000000018e69093c -[UIWebDocumentView subviews] + 88 
3 UIKit 0x000000018e941bd4 -[UIView(CALayerDelegate) _wantsReapplicationOfAutoLayoutWithLayoutDirtyOnEntry:] + 68 
4 UIKit 0x000000018e63d770 -[UIView(CALayerDelegate) layoutSublayersOfLayer:] + 1248 
5 QuartzCore 0x000000018bb0640c -[CALayer layoutSublayers] + 144 
6 QuartzCore 0x000000018bafb0e8 CA::Layer::layout_if_needed(CA::Transaction*) + 288 
7 QuartzCore 0x000000018bafafa8 CA::Layer::layout_and_display_if_needed(CA::Transaction*) + 28 
8 QuartzCore 0x000000018ba77c64 CA::Context::commit_transaction(CA::Transaction*) + 248 
9 QuartzCore 0x000000018ba9f0d0 CA::Transaction::commit() + 508 
10 QuartzCore 0x000000018ba9faf0 CA::Transaction::observer_callback(__CFRunLoopObserver*, unsigned long, void*) + 116 
11 CoreFoundation 0x00000001887a57dc __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__ + 28 
12 CoreFoundation 0x00000001887a340c __CFRunLoopDoObservers + 368 
13 CoreFoundation 0x00000001886d2068 CFRunLoopRunSpecific + 472 
14 WebCore 0x000000018d273a2c RunWebThread(void*) + 452 
15 libsystem_pthread.dylib 0x000000018788b860 _pthread_body + 236 
16 libsystem_pthread.dylib 0x000000018788b770 _pthread_start + 280 
17 libsystem_pthread.dylib 0x0000000187888dbc thread_start + 0 

任何想法是怎么回事？ 看起来像下面的崩溃组也是相关的。

崩溃组1

[UIWebBrowserView _collectAdditionalSubviews] 
objc_msgSend() selector name: autorelease 

崩溃组2

[UIWebDocumentView subviews] 
objc_msgSend() selector name: arrayByAddingObjectsFromArray: 

Answer 1

我回答我自己的问题，因为我能复制这个问题，并找到了根源。

请注意以下几点。

1.我正在使用一个UIWebView。首先，这不被推荐。

2.以下执行方式导致此问题。我在这里编写伪代码来演示问题。

@implementation MyViewController 

    - (void)loadView { 

     //creating UIWebView Here 
     self.webView = [[UIWebView alloc] initWithFrame:_some_frame]; 

     //setting the web view properties here. 

     //Adding to the view 
     [self.view addSubView: self.webView]; 

     [self populateWebView]; 
    } 

    - (void) populateWebView { 
     [self.webView loadHTMLString:_some_html 
          baseURL:[NSURL fileURLWithPath:_some_path]]; 
    } 


    - (void)viewDidLayoutSubviews { 
     [super viewDidLayoutSubviews]; 

     if (self.webView) { 
      //The following two lines causing this issue. 
      self.webView.scrollView.contentInset = _some_insets; 
      self.webView.scrollView.scrollIndicatorInsets = _some_insets; 
     } 
    } 

@end 

3.将溶液在下面给出。

@implementation MyViewController 

    - (void)loadView { 

     //creating UIWebView Here 
     self.webView = [[UIWebView alloc] initWithFrame:_some_frame]; 

     //setting the web view properties here. 

     //Adding to the view 
     [self.view addSubView: self.webView]; 

     [self populateWebView]; 
    } 

    - (void) populateWebView { 
     [self.webView loadHTMLString:_some_html 
          baseURL:[NSURL fileURLWithPath:_some_path]]; 
    } 


    - (void)viewDidLayoutSubviews { 
     [super viewDidLayoutSubviews]; 
    } 

    - (void)webViewDidFinishLoad:(UIWebView *)webView { 
     webView.scrollView.contentInset = _some_insets; 
     webView.scrollView.scrollIndicatorInsets = _some_insets; 
    } 

@end 

在我实际的代码，我在这里使用自定义的WebView类通过继承UIWebView的。不认为这会造成一些问题。根本原因是设置“contentInset”和“scrollIndicatorInsets”in viewDidLayoutSubviews这不是一个好主意。当我把折点，“viewDidLayoutSubviews”多次调用并最终导致App崩溃。

作为解决方案，我将以下代码部分移至“webViewDidFinishLoad”，只有在加载完成后WebView已准备好时才会调用该代码。因此，在此委托方法下添加此代码是有意义的。

webView.scrollView.contentInset = _some_insets; 
webView.scrollView.scrollIndicatorInsets = _some_insets;