iOS app error - Can't add self as subview

Question

I received this crash report, but I don't know how to debug it.

Fatal Exception NSInvalidArgumentException
Can't add self as subview
0 ...    CoreFoundation  __exceptionPreprocess + 130
1    libobjc.A.dylib     objc_exception_throw + 38
2    CoreFoundation  -[NSException initWithCoder:]
3    UIKit   -[UIView(Internal) _addSubview:positioned:relativeTo:] + 110
4    UIKit   -[UIView(Hierarchy) addSubview:] + 30
5    UIKit   __53-[_UINavigationParallaxTransition animateTransition:]_block_invoke + 1196
6    UIKit   +[UIView(Animation) performWithoutAnimation:] + 72
7    UIKit   -[_UINavigationParallaxTransition animateTransition:] + 732
8    UIKit   -[UINavigationController _startCustomTransition:] + 2616
9    UIKit   -[UINavigationController _startDeferredTransitionIfNeeded:] + 418
10   UIKit   -[UINavigationController __viewWillLayoutSubviews] + 44
11   UIKit   -[UILayoutContainerView layoutSubviews] + 184
12   UIKit   -[UIView(CALayerDelegate) layoutSublayersOfLayer:] + 346
13   QuartzCore  -[CALayer layoutSublayers] + 142
14   QuartzCore  CA::Layer::layout_if_needed(CA::Transaction*) + 350
15   QuartzCore  CA::Layer::layout_and_display_if_needed(CA::Transaction*) + 16
16   QuartzCore  CA::Context::commit_transaction(CA::Transaction*) + 228
17   QuartzCore  CA::Transaction::commit() + 314
18   QuartzCore  CA::Transaction::observer_callback(__CFRunLoopObserver*, unsigned long, void*) + 56

The iOS version is 7.0.3. Anyone experience this weird crash?

UPDATE:

I don't know where in my code caused this crash, so I can not post the code here, sorry.

Second UPDATE

See the answer below.

Answer 1

I will describe more details about this crash in my app and mark this as answered.

My app has a UINavigationController with the root controller is a UITableViewController that contains a list of note objects. The note object has a content property in html. Select a note will go to the detail controller.

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
    //get note object
    DetailViewController *controller = [[DetailViewController alloc] initWithNote:note];
    [self.navigationController pushViewController:controller animated:YES];
}

Detail controller

This controller has a UIWebView, display the note content passed from the root controller.

- (void)viewDidLoad
{
    ...
    [_webView loadHTMLString:note.content baseURL:nil];
    ...
}

This controller is the delegate of the webview control. If the note contains links, tap a link will go to the in-app web browser.

- (BOOL)webView:(UIWebView *)webView shouldStartLoadWithRequest:(NSURLRequest *)request navigationType:(UIWebViewNavigationType)navigationType
{
    WebBrowserViewController *browserController = [[WebBrowserViewController alloc] init];
    browserController.startupURL = request.URL;
    [self.navigationController pushViewController:webViewController animated:YES];
    return NO;
}

I received the above crash report everyday. I don't know where in my code caused this crash. After some investigates with the help of a user, I was finally able to fix this crash. This html content will cause the crash:

...
<iframe src="http://google.com"></iframe>
...

In the viewDidLoad method of the detail controller, I loaded this html to the webview control, right after that, the above delegate method was called immediately with request.URL is the iframe's source (google.com). This delegate method calls pushViewController method while in viewDidLoad => crash!

I fixed this crash by checking the navigationType:

- (BOOL)webView:(UIWebView *)webView shouldStartLoadWithRequest:(NSURLRequest *)request navigationType:(UIWebViewNavigationType)navigationType
{
    if (navigationType != UIWebViewNavigationTypeOther)
    {
        //go to web browser controller
    }
}

Hope this helps