iOS UIWebView TextField - Application crash on hitting Done button on keyboard after entering text

I have several webviews in my app. Few of the webviews will have a textfield in them.

When running the app initially, on entering some text in the textfield and hitting the 'Done' button on the keyboard causes the app to crash. If I relaunch the app and try the same scenario, it works fine.

I am running few Javascript files as well in the WebView.

This is the error thrown:

EXC_BAD_ACCESS mh_execute_header
Attempted to dereference null pointer.

This is the trace I got from the crash details:

/usr/lib/libobjc.A.dylib:0objc_msgSend  
Frameworks/UIKit.framework/UIKit:0-[_UIWebViewScrollViewDelegateForwarder forwardInvocation:]   
Frameworks/CoreFoundation.framework/CoreFoundation:0___forwarding___    
Frameworks/CoreFoundation.framework/CoreFoundation:0__forwarding_prep_0___  
Frameworks/UIKit.framework/UIKit:0-[UIScrollView _getDelegateZoomView]  
Frameworks/UIKit.framework/UIKit:0-[UIScrollView _zoomScaleFromPresentationLayer:]  
Frameworks/UIKit.framework/UIKit:0-[UIWebDocumentView _zoomedDocumentScale] 
Frameworks/UIKit.framework/UIKit:0-[UIWebDocumentView _layoutRectForFixedPositionObjects]   
Frameworks/UIKit.framework/UIKit:0-[UIWebDocumentView _updateFixedPositionedObjectsLayoutRectUsingWebThread:synchronize:]   
Frameworks/UIKit.framework/UIKit:0-[UIWebDocumentView _updateFixedPositioningObjectsLayoutAfterScroll]  
Frameworks/UIKit.framework/UIKit:0-[UIWebBrowserView _updateFixedPositioningObjectsLayoutAfterScroll]   
Frameworks/CoreFoundation.framework/CoreFoundation:0__CFNOTIFICATIONCENTER_IS_CALLING_OUT_TO_AN_OBSERVER__  
Frameworks/CoreFoundation.framework/CoreFoundation:0_CFXRegistrationPost    
Frameworks/CoreFoundation.framework/CoreFoundation:0___CFXNotificationPost_block_invoke 
Frameworks/CoreFoundation.framework/CoreFoundation:0-[_CFXNotificationRegistrar find:object:observer:enumerator:]   
Frameworks/CoreFoundation.framework/CoreFoundation:0_CFXNotificationPost    
Frameworks/Foundation.framework/Foundation:0-[NSNotificationCenter postNotificationName:object:userInfo:]   
Frameworks/UIKit.framework/UIKit:0-[UIInputWindowController postEndNotifications:withInfo:] 
Frameworks/UIKit.framework/UIKit:0__77-[UIInputWindowController moveFromPlacement:toPlacement:starting:completion:]_block_invoke_2896   
Frameworks/UIKit.framework/UIKit:0-[UIInputWindowController performWithSafeTransitionFrames:]   
Frameworks/UIKit.framework/UIKit:0__77-[UIInputWindowController moveFromPlacement:toPlacement:starting:completion:]_block_invoke887 
Frameworks/UIKit.framework/UIKit:0-[UIViewAnimationBlockDelegate _didEndBlockAnimation:finished:context:]   
Frameworks/UIKit.framework/UIKit:0-[UIViewAnimationState sendDelegateAnimationDidStop:finished:]    
Frameworks/UIKit.framework/UIKit:0-[UIViewAnimationState animationDidStop:finished:]    
Frameworks/QuartzCore.framework/QuartzCore:0<redacted>  
/usr/lib/system/libdispatch.dylib:0_dispatch_client_callout 
/usr/lib/system/libdispatch.dylib:0_dispatch_main_queue_callback_4CF    
Frameworks/CoreFoundation.framework/CoreFoundation:0__CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__  
Frameworks/CoreFoundation.framework/CoreFoundation:0__CFRunLoopRun  
Frameworks/CoreFoundation.framework/CoreFoundation:0CFRunLoopRunSpecific    
PrivateFrameworks/GraphicsServices.framework/GraphicsServices:0GSEventRunModal  
Frameworks/UIKit.framework/UIKit:0-[UIApplication runModal:]    
Frameworks/UIKit.framework/UIKit:0-[UIAlertView _showAnimated:] 
Frameworks/UIKit.framework/UIKit:0-[UIWebView webView:runJavaScriptAlertPanelWithMessage:initiatedByFrame:] 
Frameworks/CoreFoundation.framework/CoreFoundation:0__invoking___   
Frameworks/CoreFoundation.framework/CoreFoundation:0-[NSInvocation invoke]  
Frameworks/CoreFoundation.framework/CoreFoundation:0-[NSInvocation invokeWithTarget:]   
PrivateFrameworks/WebKitLegacy.framework/WebKitLegacy:0<redacted>   
Frameworks/CoreFoundation.framework/CoreFoundation:0___forwarding___    
Frameworks/CoreFoundation.framework/CoreFoundation:0__forwarding_prep_0___  
PrivateFrameworks/WebKitLegacy.framework/WebKitLegacy:0<redacted>   
PrivateFrameworks/WebCore.framework/WebCore:0<redacted> 
PrivateFrameworks/WebCore.framework/WebCore:0<redacted> 
Frameworks/JavaScriptCore.framework/JavaScriptCore:0<redacted>  
Frameworks/JavaScriptCore.framework/JavaScriptCore:0<redacted>  
Frameworks/JavaScriptCore.framework/JavaScriptCore:0<redacted>  
Frameworks/JavaScriptCore.framework/JavaScriptCore:0<redacted>  
Frameworks/JavaScriptCore.framework/JavaScriptCore:0<redacted>  
Frameworks/JavaScriptCore.framework/JavaScriptCore:0<redacted>  
Frameworks/JavaScriptCore.framework/JavaScriptCore:0<redacted>  
Frameworks/JavaScriptCore.framework/JavaScriptCore:0JSC::call(JSC::ExecState*, JSC::JSValue, JSC::CallType, JSC::CallData const&, JSC::JSValue, JSC::ArgList const&, WTF::NakedPtr<JSC::Exception>&)    
PrivateFrameworks/WebCore.framework/WebCore:0<redacted> 
PrivateFrameworks/WebCore.framework/WebCore:0<redacted> 
PrivateFrameworks/WebCore.framework/WebCore:0<redacted> 
PrivateFrameworks/WebCore.framework/WebCore:0<redacted> 
PrivateFrameworks/WebCore.framework/WebCore:0<redacted> 
PrivateFrameworks/WebCore.framework/WebCore:0<redacted> 
PrivateFrameworks/WebCore.framework/WebCore:0WebCore::EventHandler::keyEvent(WebCore::PlatformKeyboardEvent const&) 
PrivateFrameworks/WebCore.framework/WebCore:0WebCore::EventHandler::keyEvent(WebEvent*) 
Frameworks/CoreFoundation.framework/CoreFoundation:0__invoking___   
Frameworks/CoreFoundation.framework/CoreFoundation:0-[NSInvocation invoke]  
Frameworks/CoreFoundation.framework/CoreFoundation:0-[NSInvocation invokeWithTarget:]   
Frameworks/UIKit.framework/UIKit:0-[UIThreadSafeNode forwardInvocation:]    
Frameworks/CoreFoundation.framework/CoreFoundation:0___forwarding___    
Frameworks/CoreFoundation.framework/CoreFoundation:0__forwarding_prep_0___  
Frameworks/UIKit.framework/UIKit:0-[UIKeyboardImpl _handleWebKeyEvent:withEventType:withInputString:withInputStringIgnoringModifiers:]  
Frameworks/UIKit.framework/UIKit:0__78-[UIKeyboardImpl _handleWebKeyEvent:withIndex:inInputString:executionContext:]_block_invoke   
Frameworks/UIKit.framework/UIKit:0-[UIKeyboardTaskExecutionContext returnExecutionToParentWithInfo:]    
Frameworks/UIKit.framework/UIKit:0-[UIKeyboardTaskExecutionContext returnExecutionToParentWithInfo:]    
Frameworks/UIKit.framework/UIKit:0-[UIKeyboardTaskQueue continueExecutionOnMainThread]  
Frameworks/Foundation.framework/Foundation:0__NSThreadPerformPerform    
Frameworks/CoreFoundation.framework/CoreFoundation:0__CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__  
Frameworks/CoreFoundation.framework/CoreFoundation:0__CFRunLoopDoSources0   
Frameworks/CoreFoundation.framework/CoreFoundation:0__CFRunLoopRun  
Frameworks/CoreFoundation.framework/CoreFoundation:0CFRunLoopRunSpecific    
PrivateFrameworks/GraphicsServices.framework/GraphicsServices:0GSEventRunModal  
Frameworks/UIKit.framework/UIKit:0UIApplicationMain 
MyApp:0mh_execute_header    
/usr/lib/system/libdyld.dylib:0<redacted>

I really am not sure as to why is this crash happening.

TIA!

Solution

I was able to get this crash fixed by doing the following:

Put a Javascript callback when the keyboard is dismissed
Fetch the callback in

func webView(webView: UIWebView, shouldStartLoadWithRequest request: NSURLRequest, navigationType: UIWebViewNavigationType) -> Bool

Set the content offset of WebView's ScrollView:

webView.scrollView.setContentOffset(CGPointMake(0, 0), animated: false)

I had a bunch of WebViews inside a ScrollView. I know this is not ideal, but I had to go ahead with this.

When the keyboard is dismissed, the WebView tries to scroll to a position which does not exist and cause the app to crash.

So by doing the callback method, I scroll the WebView to the top, once the keyboard is dismissed.