键入时，导航控制器内的UIWebView崩溃

Question

I've spent a few hours searching for a solution to this problem but I can't even seem to find anyone who's experienced it, let alone a solution.

In my project, I have a main view controller that pushes a second view controller containing a UIWebView. Both view controllers are embedded in a navigation controller. The push segue and WebView are both hooked up using IB.

The segue happens as expected and the web page loads and works fine until I try to type. Tapping on a text field brings up the keyboard, but the first key press crashes the app and gives the error:

-[NSNull length]: unrecognized selector sent to instance 0x1899068
2014-02-06 04:37:19.550 *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSNull length]: unrecognized selector sent to instance 0x1899068'
*** First throw call stack:
(
    0   CoreFoundation                      0x0174d5e4 __exceptionPreprocess + 180
    1   libobjc.A.dylib                     0x014d08b6 objc_exception_throw + 44
...

This happens both in the Simulator and on device. I'm particularly confused because I'm not doing anything remotely complex. In the view controller that contains the WebView, I have the following viewDidLoad:

- (void)viewDidLoad {
    [super viewDidLoad];

    NSURL *url = [NSURL URLWithString:@"http://www.google.com"];
    NSURLRequest *request = [NSURLRequest requestWithURL:url];

    [self.webView loadRequest:request];
}

and no other code. Google is used as an example site here, but it happens on every site I've tried. The weird thing is that if I remove the segue and present the Web View without the parent Navigation Controller, everything works fine, so it seems like the nav controller has something to do with it. As I said, the webView property is hooked up as an IB outlet. I've also tried adding it programatically, but the outcome was the same. As far as I can tell nothing in my first view controller should have any effect on this; like I said it's a Storyboard segue from a button. I can be sure sending length to NSNull is not anything I'm doing directly by myself, as I don't use the length selector anywhere in my code.

Any help would be greatly appreciated.

It was requested so the full error message is as follows:

-[NSNull length]: unrecognized selector sent to instance 0x1899068
2014-02-06 05:18:29.607 AppName[859:70b] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSNull length]: unrecognized selector sent to instance 0x1899068'
*** First throw call stack:
(
    0   CoreFoundation                      0x0174d5e4 __exceptionPreprocess + 180
    1   libobjc.A.dylib                     0x014d08b6 objc_exception_throw + 44
    2   CoreFoundation                      0x017ea903 -[NSObject(NSObject) doesNotRecognizeSelector:] + 275
    3   CoreFoundation                      0x0173d90b ___forwarding___ + 1019
    4   CoreFoundation                      0x0173d4ee _CF_forwarding_prep_0 + 14
    5   CoreFoundation                      0x016cd95c CFStringGetLength + 140
    6   CoreFoundation                      0x016e1284 CFStringCompareWithOptionsAndLocale + 52
    7   Foundation                          0x010db634 -[NSString compare:options:range:locale:] + 175
    8   Foundation                          0x010db580 -[NSString compare:options:range:] + 69
    9   Foundation                          0x010eda59 -[NSString caseInsensitiveCompare:] + 80
    10  UIKit                               0x00454f48 -[UIPhysicalKeyboardEvent _matchesKeyCommand:] + 280
    11  UIKit                               0x00398ac9 -[UIResponder(Internal) _keyCommandForEvent:] + 312
    12  UIKit                               0x00398b3b -[UIResponder(Internal) _keyCommandForEvent:] + 426
    13  UIKit                               0x00398b3b -[UIResponder(Internal) _keyCommandForEvent:] + 426
    14  UIKit                               0x00398b3b -[UIResponder(Internal) _keyCommandForEvent:] + 426
    15  UIKit                               0x00398b3b -[UIResponder(Internal) _keyCommandForEvent:] + 426
    16  UIKit                               0x00398b3b -[UIResponder(Internal) _keyCommandForEvent:] + 426
    17  UIKit                               0x00398b3b -[UIResponder(Internal) _keyCommandForEvent:] + 426
    18  UIKit                               0x00398b3b -[UIResponder(Internal) _keyCommandForEvent:] + 426
    19  UIKit                               0x00398b3b -[UIResponder(Internal) _keyCommandForEvent:] + 426
    20  UIKit                               0x00252176 -[UIApplication handleKeyHIDEvent:] + 226
    21  UIKit                               0x0023a07c _UIApplicationHandleEventQueue + 2954
    22  CoreFoundation                      0x016d683f __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 15
    23  CoreFoundation                      0x016d61cb __CFRunLoopDoSources0 + 235
    24  CoreFoundation                      0x016f329e __CFRunLoopRun + 910
    25  CoreFoundation                      0x016f2ac3 CFRunLoopRunSpecific + 467
    26  CoreFoundation                      0x016f28db CFRunLoopRunInMode + 123
    27  GraphicsServices                    0x036f29e2 GSEventRunModal + 192
    28  GraphicsServices                    0x036f2809 GSEventRun + 104
    29  UIKit                               0x0023ed3b UIApplicationMain + 1225
    30  AppName                             0x00003d3d main + 141
    31  libdyld.dylib                       0x01d8b70d start + 1
    32  ???                                 0x00000001 0x0 + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException

Answer 1

So I managed to fix this by not really doing anything. What eventually fixed it was deleting the Navigation Controller that all the VCs were embedded in, then embedding them back in a Nav Controller. Now it works completely. So I don't know if it was an errant setting or what.

Answer 2

@deergomoo sorry for my first answer. I wash it as false.

So, what do you think about next example? Is it similar to your project structure? I can't find crashes.

@implementation AppDelegate

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    UINavigationController *navController=[UINavigationController new];
    ViewController *viewController=[[ViewController alloc] init];
    [navController pushViewController:viewController animated:NO];
    self.window.rootViewController = navController;
    [self.window makeKeyAndVisible];

    return YES;
}

.

#import "ViewController.h"

@implementation ViewController

-  (void)viewDidLoad {
    [super viewDidLoad];

    UITableView *tableView = [[UITableView alloc] initWithFrame:self.view.bounds
                                                          style:UITableViewStylePlain];
    tableView.delegate = self;
    tableView.dataSource = self;
    [self.view addSubview:tableView];
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
    return 1;
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    UITableViewCell *cell = [[UITableViewCell alloc] initWithStyle: UITableViewCellStyleDefault
                                                   reuseIdentifier:nil];
    cell.textLabel.text = @"Cell";
    return cell;
}

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
    NSLog(@"didSelectRowAtIndexPath");
    UIViewController *viewController = [UIViewController new];
    UIWebView *webView = [[UIWebView alloc] initWithFrame:self.view.bounds];
    [viewController.view addSubview:webView];

    NSURL *url = [NSURL URLWithString:@"http://www.google.com"];
    NSURLRequest *request = [NSURLRequest requestWithURL:url];

    [webView loadRequest:request];

    [self.navigationController pushViewController:viewController animated:TRUE];
}

@end

Answer 3

In my case I guess my tab bar controller had become corrupt in my storyboard. I had to remove all the view controller outlets from it. Delete the tab bar controller. Clean the project. Add a new tab bar controller and re-wire all the outlets. Then I stopped seeing this crash.

I just mention it so it may help someone else.