iOS 7应用在UITextField输入上崩溃

Question

I'm trying to develop a questionnaire app where sometimes, a string must be inputted. In interface builder I have a scroll view, and in it a UITextField. But when I run it in the simulator, the app crashes when I try to input a simple string into it. The keyboard shows up, but as soon as I try to type something, I get a SIGARBT on the main function. The complete error message (don't mind the app name, it's just a simple test app that I made in a few minutes):

2014-03-08 18:16:38.564 hetisweertijdvoordepolonaise[4381:70b] -[NSNull length]: unrecognized selector sent to instance 0x1898068
2014-03-08 18:16:38.569 hetisweertijdvoordepolonaise[4381:70b] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSNull length]: unrecognized selector sent to instance 0x1898068'
*** First throw call stack:
(
    0   CoreFoundation                      0x0174c5e4 __exceptionPreprocess + 180
    1   libobjc.A.dylib                     0x014bb8b6 objc_exception_throw + 44
    2   CoreFoundation                      0x017e9903 -[NSObject(NSObject) doesNotRecognizeSelector:] + 275
    3   CoreFoundation                      0x0173c90b ___forwarding___ + 1019
    4   CoreFoundation                      0x0173c4ee _CF_forwarding_prep_0 + 14
    5   CoreFoundation                      0x016cc95c CFStringGetLength + 140
    6   CoreFoundation                      0x016e0284 CFStringCompareWithOptionsAndLocale + 52
    7   Foundation                          0x010c6634 -[NSString compare:options:range:locale:] + 175
    8   Foundation                          0x010c6580 -[NSString compare:options:range:] + 69
    9   Foundation                          0x010d8a59 -[NSString caseInsensitiveCompare:] + 80
    10  UIKit                               0x0043ff48 -[UIPhysicalKeyboardEvent _matchesKeyCommand:] + 280
    11  UIKit                               0x00383ac9 -[UIResponder(Internal) _keyCommandForEvent:] + 312
    12  UIKit                               0x00383b3b -[UIResponder(Internal) _keyCommandForEvent:] + 426
    13  UIKit                               0x00383b3b -[UIResponder(Internal) _keyCommandForEvent:] + 426
    14  UIKit                               0x00383b3b -[UIResponder(Internal) _keyCommandForEvent:] + 426
    15  UIKit                               0x00383b3b -[UIResponder(Internal) _keyCommandForEvent:] + 426
    16  UIKit                               0x0023d34b -[UIApplication _handleKeyUIEvent:] + 138
    17  UIKit                               0x00383fa4 -[UIResponder(Internal) _handleKeyUIEvent:] + 59
    18  UIKit                               0x00383fa4 -[UIResponder(Internal) _handleKeyUIEvent:] + 59
    19  UIKit                               0x00383fa4 -[UIResponder(Internal) _handleKeyUIEvent:] + 59
    20  UIKit                               0x00383fa4 -[UIResponder(Internal) _handleKeyUIEvent:] + 59
    21  UIKit                               0x00383fa4 -[UIResponder(Internal) _handleKeyUIEvent:] + 59
    22  UIKit                               0x00383fa4 -[UIResponder(Internal) _handleKeyUIEvent:] + 59
    23  UIKit                               0x0023d2ba -[UIApplication handleKeyUIEvent:] + 84
    24  UIKit                               0x00413d29 -[UIKeyboardImpl _handleKeyEvent:executionContext:] + 80
    25  UIKit                               0x0058d179 -[UIKeyboardLayoutStar completeRetestForTouchUp:timestamp:interval:executionContext:] + 4078
    26  UIKit                               0x0058bc7f -[UIKeyboardLayoutStar touchUp:executionContext:] + 1545
    27  UIKit                               0x00421f18 __28-[UIKeyboardLayout touchUp:]_block_invoke + 269
    28  UIKit                               0x009383c8 -[UIKeyboardTaskQueue continueExecutionOnMainThread] + 402
    29  UIKit                               0x00938a6f -[UIKeyboardTaskQueue addTask:] + 144
    30  UIKit                               0x00421e03 -[UIKeyboardLayout touchUp:] + 263
    31  UIKit                               0x00422939 -[UIKeyboardLayout touchesEnded:withEvent:] + 362
    32  UIKit                               0x0026851d -[UIWindow _sendTouchesForEvent:] + 852
    33  UIKit                               0x00269184 -[UIWindow sendEvent:] + 1232
    34  UIKit                               0x0023ce86 -[UIApplication sendEvent:] + 242
    35  UIKit                               0x0022718f _UIApplicationHandleEventQueue + 11421
    36  CoreFoundation                      0x016d583f __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 15
    37  CoreFoundation                      0x016d51cb __CFRunLoopDoSources0 + 235
    38  CoreFoundation                      0x016f229e __CFRunLoopRun + 910
    39  CoreFoundation                      0x016f1ac3 CFRunLoopRunSpecific + 467
    40  CoreFoundation                      0x016f18db CFRunLoopRunInMode + 123
    41  GraphicsServices                    0x036dd9e2 GSEventRunModal + 192
    42  GraphicsServices                    0x036dd809 GSEventRun + 104
    43  UIKit                               0x00229d3b UIApplicationMain + 1225
    44  hetisweertijdvoordepolonaise        0x0000204d main + 141
    45  libdyld.dylib                       0x01d76701 start + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException
(lldb) 

ViewController.m:

#import "ViewController.h"

@interface ViewController ()

@end

@implementation ViewController

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

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

@end

Is there some fundamental thing I forgot?

Answer 1

According to the stack trace, maybe you have initialized a NSString incorrectly. Please paste the relevant code.

Answer 2

This is a shot in the dark without seeing more of your code. Looking at the stacktrace, it seems like your code is misinterpreting your text input as a key command for some reason. It is trying to compare your input against a set of known commands and failing.

There are a few other things that might be related since you are running in the simulator. In the 'hardware' menu is 'simulate hardware keyboard' checked? What about 'IOS uses same layout as OSX'?

One last thing. If you really want people to be able to reproduce this issue, we need to see the UI code. If you right click on your storyboard file and select 'open as' there is an option to view the file as source code. For an app as simple as what you described, the text should be small enough that you can paste it here or host it somewhere and provide a link.