Try/Catch around LPInvoker invokeSelector:withTarget:

[jmoody]

Motivation

NSNumber is receiving an unrecognized selector isEqualToString:.

This is being thrown when we ask for the accessibilityLabel of a UITextField.

As far as I can tell, we are not directly responsible for calling isEqualToString on the NSNumber instance.

Stack trace

    NSInvalidArgumentException: -[__NSCFNumber isEqualToString:]: unrecognized selector sent to instance 0x7ae719c0
        0   CoreFoundation                      0x0768c746 __exceptionPreprocess + 182
        1   libobjc.A.dylib                     0x07a31a97 objc_exception_throw + 44
        2   CoreFoundation                      0x07694705 -[NSObject(NSObject) doesNotRecognizeSelector:] + 277
        3   CoreFoundation                      0x075db287 ___forwarding___ + 1047
        4   CoreFoundation                      0x075dae4e _CF_forwarding_prep_0 + 14
        5   MessageUIFramework                  0x18ed0f28 -[UIMessageUITextFieldAccessibility accessibilityLabel] + 90
        6   CoreFoundation                      0x0756d84d __invoking___ + 29
        7   CoreFoundation                      0x0756d6f8 -[NSInvocation invoke] + 360
        8   PatientHubFrameworkTouch            0x00128461 +[LPInvoker invokeSelector:withTarget:] + 545
        9   PatientHubFrameworkTouch            0x0011e96d +[LPJSONUtils dictionary:setObjectforKey:whenTarget:respondsTo:] + 221
        10  PatientHubFrameworkTouch            0x001201c9 +[LPJSONUtils dictionaryByEncodingView:] + 809
        11  PatientHubFrameworkTouch            0x0011f7bc +[LPJSONUtils jsonifyObject:fullDump:] + 876
        12  PatientHubFrameworkTouch            0x0011f412 +[LPJSONUtils jsonifyObject:] + 98
        13  PatientHubFrameworkTouch            0x000f6f06 -[LPQueryAllOperation performWithTarget:error:] + 134
        14  PatientHubFrameworkTouch            0x000f9b89 -[LPQueryOperation performWithTarget:error:] + 89

Catching the exception

PatientHubFrameworkTouch[11661]: LPInvoker caught an exception: -[__NSCFNumber isEqualToString:]: 
                                 unrecognized selector sent to instance 0x7b783860
PatientHubFrameworkTouch[11661]: === INVOCATION DETAILS ===
PatientHubFrameworkTouch[11661]: target = <UITextField: 0x7b616aa0; frame = (58 268; 204 30); text = 'Password1'; clipsToBounds = YES; opaque = NO; autoresize = RM+BM; gestureRecognizers = <NSArray: 0x7e1572c0>; layer = <CALayer: 0x7b61bd40>>
PatientHubFrameworkTouch[11661]: target class = UITextField
PatientHubFrameworkTouch[11661]: selector = accessibilityLabel
PatientHubFrameworkTouch[11661]: target responds to selector: YES

Analysis

My best guess is that UIMessageUITextFieldAccessibility is part of the UITextField class cluster. I cannot find this class in the iOS 8 private header sources.[1][2] It does appear in the iOS 7 SDK.

The fact that we are not directly involved in calling isEqualToString on an NSNumber instance, makes me think this is an Apple bug.

• [1] https://github.com/nst/iOS-Runtime-Headers
• [2] https://github.com/ichitaso/iOS-iphoneheaders

[jmoody]

@krukow

[krukow]

@jmoody well done -- I agree this is a bug on Apple's side: accessibilityLabel is typed to return (NSString*)

[jmoody]

@krukow

At first glance, I thought the accessibilityLabel call was the direct cause of the crash.

Looking deeper and logging the invocation call, I can see the exception is happening much further down the stack somewhere in the internals of UIMessageUITextFieldAccessibility.

If you query the text view in question directly, you'll see that you can, without an exception, get back the accessibilityValue.

[jmoody]

The actual problem was caused by the user creating a Runtime Attribute accessibilityLabel with type "NSNumber".