UIWebDocumentView _updateSubviewCache crash in iOS10

Question

In iOS10, I take HockeyApp crash more seriously. Please find the crash log as shown below.

Thread 4 Crashed:

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

Any idea what is going on here? The following failure groups also seem to be related.

Crash Group 1

[UIWebBrowserView _collectAdditionalSubviews]
objc_msgSend() selector name: autorelease

Crash Group 2

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

Answer 1

I answer my question, as I can reproduce this problem and found the root cause.

Pay attention to the following.

1. I am using UIWebView. First of all, it is not recommended.

2. The following implementation method causes this problem. Here I write pseudo code to demonstrate the problem.

@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. The solution is given below.

@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

WebView, UIWebView. , . contentInset "" scrollIndicatorInsets " viewDidLayoutSubviews, . ," viewDidLayoutSubviews" , , .

" webViewDidFinishLoad", , WebView . .

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