Scrolling through UITableView causes Exception and Crash only on iPhone 5C

Question

There is an exception being thrown when a user scrolls through my UITableView too fast or taps the status bar to jump to the top of the table. I am only seeing this crash on an iPhone 5C device. I can't reproduce it on the 4S, 5, or with the 32-bit simulator.

Using the "All Exceptions" breakpoint, I was able to print out all the backtraces I could incrementing the frame pointer through the crash. Because there is no trace of my app in the backtrace (besides the main), I assume this is an Apple bug, something to do with [NSRLEArray objectAtIndex:effectiveRange:]. The author of this question seemed to have the same problem with an OS X application, and a comment suggested looking at the NSAttributedString usage in my app. I do use NSAttributedStrings in my table view cells to hyperlink certain strings in a UITextView. But if it was a general issue with NSAttributedString, wouldn't this also cause a crash on other iOS devices?

Backtrace:

(lldb) bt
* thread #1: tid = 0x2e57bd, 0x3978e6a0 libobjc.A.dylib`objc_exception_throw, queue = 'com.apple.main-thread', stop reason = breakpoint 1.1
    frame #0: 0x3978e6a0 libobjc.A.dylib`objc_exception_throw
    frame #1: 0x2f431dc4 CoreFoundation`+[NSException raise:format:] + 112
    frame #2: 0x2fd55230 Foundation`-[NSRLEArray objectAtIndex:effectiveRange:] + 120
    frame #3: 0x2fd71d76 Foundation`-[NSConcreteMutableAttributedString addAttribute:value:range:] + 198
    frame #4: 0x36d7b278 UIFoundation`__50-[NSConcreteTextStorage addAttribute:value:range:]_block_invoke + 156
    frame #5: 0x36d7b102 UIFoundation`-[NSConcreteTextStorage addAttribute:value:range:] + 170
    frame #6: 0x337fc02e DataDetectorsUI`-[DDTextKitOperation _addResultsToAttributes] + 266
    frame #7: 0x337fc1d6 DataDetectorsUI`__46-[DDTextKitOperation doURLificationOnDocument]_block_invoke_2 + 26
    frame #8: 0x36d79a5e UIFoundation`-[NSTextStorage(ActorSupport) coordinateAccess:] + 34
    frame #9: 0x337fc1b8 DataDetectorsUI`__46-[DDTextKitOperation doURLificationOnDocument]_block_invoke + 116
    frame #10: 0x39c78bde libdispatch.dylib`_dispatch_barrier_sync_f_slow_invoke + 66
    frame #11: 0x39c730ae libdispatch.dylib`_dispatch_client_callout + 22
    frame #12: 0x39c759a8 libdispatch.dylib`_dispatch_main_queue_callback_4CF + 268
    frame #13: 0x2f3fc5b0 CoreFoundation`__CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__ + 8
    frame #14: 0x2f3fae7c CoreFoundation`__CFRunLoopRun + 1308
    frame #15: 0x2f365470 CoreFoundation`CFRunLoopRunSpecific + 524
    frame #16: 0x2f365252 CoreFoundation`CFRunLoopRunInMode + 106
    frame #17: 0x3409f2ea GraphicsServices`GSEventRunModal + 138
    frame #18: 0x31c1a844 UIKit`UIApplicationMain + 1136
  * frame #19: 0x000bffb4 [AppName]`main(argc=1, argv=0x27d4ecec) + 116 at main.m:16
(lldb) bt
* thread #1: tid = 0x2e57bd, 0x39153994 libc++abi.dylib`__cxa_throw, queue = 'com.apple.main-thread', stop reason = breakpoint 1.2
    frame #0: 0x39153994 libc++abi.dylib`__cxa_throw
    frame #1: 0x3978e79a libobjc.A.dylib`objc_exception_throw + 250
    frame #2: 0x2f431dc4 CoreFoundation`+[NSException raise:format:] + 112
    frame #3: 0x2fd55230 Foundation`-[NSRLEArray objectAtIndex:effectiveRange:] + 120
    frame #4: 0x2fd71d76 Foundation`-[NSConcreteMutableAttributedString addAttribute:value:range:] + 198
    frame #5: 0x36d7b278 UIFoundation`__50-[NSConcreteTextStorage addAttribute:value:range:]_block_invoke + 156
    frame #6: 0x36d7b102 UIFoundation`-[NSConcreteTextStorage addAttribute:value:range:] + 170
    frame #7: 0x337fc02e DataDetectorsUI`-[DDTextKitOperation _addResultsToAttributes] + 266
    frame #8: 0x337fc1d6 DataDetectorsUI`__46-[DDTextKitOperation doURLificationOnDocument]_block_invoke_2 + 26
    frame #9: 0x36d79a5e UIFoundation`-[NSTextStorage(ActorSupport) coordinateAccess:] + 34
    frame #10: 0x337fc1b8 DataDetectorsUI`__46-[DDTextKitOperation doURLificationOnDocument]_block_invoke + 116
    frame #11: 0x39c78bde libdispatch.dylib`_dispatch_barrier_sync_f_slow_invoke + 66
    frame #12: 0x39c730ae libdispatch.dylib`_dispatch_client_callout + 22
    frame #13: 0x39c759a8 libdispatch.dylib`_dispatch_main_queue_callback_4CF + 268
    frame #14: 0x2f3fc5b0 CoreFoundation`__CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__ + 8
    frame #15: 0x2f3fae7c CoreFoundation`__CFRunLoopRun + 1308
    frame #16: 0x2f365470 CoreFoundation`CFRunLoopRunSpecific + 524
    frame #17: 0x2f365252 CoreFoundation`CFRunLoopRunInMode + 106
    frame #18: 0x3409f2ea GraphicsServices`GSEventRunModal + 138
    frame #19: 0x31c1a844 UIKit`UIApplicationMain + 1136
  * frame #20: 0x000bffb4 [AppName]`main(argc=1, argv=0x27d4ecec) + 116 at main.m:16
(lldb) bt
* thread #1: tid = 0x2e57bd, 0x3978e6a0 libobjc.A.dylib`objc_exception_throw, queue = 'com.apple.main-thread', stop reason = breakpoint 1.1
    frame #0: 0x3978e6a0 libobjc.A.dylib`objc_exception_throw
    frame #1: 0x2f431b88 CoreFoundation`-[NSException raise] + 8
    frame #2: 0x36d7b19a UIFoundation`-[NSConcreteTextStorage addAttribute:value:range:] + 322
    frame #3: 0x337fc02e DataDetectorsUI`-[DDTextKitOperation _addResultsToAttributes] + 266
    frame #4: 0x337fc1d6 DataDetectorsUI`__46-[DDTextKitOperation doURLificationOnDocument]_block_invoke_2 + 26
    frame #5: 0x36d79a5e UIFoundation`-[NSTextStorage(ActorSupport) coordinateAccess:] + 34
    frame #6: 0x337fc1b8 DataDetectorsUI`__46-[DDTextKitOperation doURLificationOnDocument]_block_invoke + 116
    frame #7: 0x39c78bde libdispatch.dylib`_dispatch_barrier_sync_f_slow_invoke + 66
    frame #8: 0x39c730ae libdispatch.dylib`_dispatch_client_callout + 22
    frame #9: 0x39c759a8 libdispatch.dylib`_dispatch_main_queue_callback_4CF + 268
    frame #10: 0x2f3fc5b0 CoreFoundation`__CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__ + 8
    frame #11: 0x2f3fae7c CoreFoundation`__CFRunLoopRun + 1308
    frame #12: 0x2f365470 CoreFoundation`CFRunLoopRunSpecific + 524
    frame #13: 0x2f365252 CoreFoundation`CFRunLoopRunInMode + 106
    frame #14: 0x3409f2ea GraphicsServices`GSEventRunModal + 138
    frame #15: 0x31c1a844 UIKit`UIApplicationMain + 1136
  * frame #16: 0x000bffb4 [AppName]`main(argc=1, argv=0x27d4ecec) + 116 at main.m:16
(lldb) bt
* thread #1: tid = 0x2e57bd, 0x39153994 libc++abi.dylib`__cxa_throw, queue = 'com.apple.main-thread', stop reason = breakpoint 1.2
    frame #0: 0x39153994 libc++abi.dylib`__cxa_throw
    frame #1: 0x3978e79a libobjc.A.dylib`objc_exception_throw + 250
    frame #2: 0x2f431b88 CoreFoundation`-[NSException raise] + 8
    frame #3: 0x36d7b19a UIFoundation`-[NSConcreteTextStorage addAttribute:value:range:] + 322
    frame #4: 0x337fc02e DataDetectorsUI`-[DDTextKitOperation _addResultsToAttributes] + 266
    frame #5: 0x337fc1d6 DataDetectorsUI`__46-[DDTextKitOperation doURLificationOnDocument]_block_invoke_2 + 26
    frame #6: 0x36d79a5e UIFoundation`-[NSTextStorage(ActorSupport) coordinateAccess:] + 34
    frame #7: 0x337fc1b8 DataDetectorsUI`__46-[DDTextKitOperation doURLificationOnDocument]_block_invoke + 116
    frame #8: 0x39c78bde libdispatch.dylib`_dispatch_barrier_sync_f_slow_invoke + 66
    frame #9: 0x39c730ae libdispatch.dylib`_dispatch_client_callout + 22
    frame #10: 0x39c759a8 libdispatch.dylib`_dispatch_main_queue_callback_4CF + 268
    frame #11: 0x2f3fc5b0 CoreFoundation`__CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__ + 8
    frame #12: 0x2f3fae7c CoreFoundation`__CFRunLoopRun + 1308
    frame #13: 0x2f365470 CoreFoundation`CFRunLoopRunSpecific + 524
    frame #14: 0x2f365252 CoreFoundation`CFRunLoopRunInMode + 106
    frame #15: 0x3409f2ea GraphicsServices`GSEventRunModal + 138
    frame #16: 0x31c1a844 UIKit`UIApplicationMain + 1136
  * frame #17: 0x000bffb4 [AppName]`main(argc=1, argv=0x27d4ecec) + 116 at main.m:16
(lldb) bt
* thread #1: tid = 0x2e57bd, 0x39d3e1fc libsystem_kernel.dylib`__pthread_kill + 8, queue = 'com.apple.main-thread', stop reason = signal SIGABRT
    frame #0: 0x39d3e1fc libsystem_kernel.dylib`__pthread_kill + 8
    frame #1: 0x39da5a52 libsystem_pthread.dylib`pthread_kill + 58
    frame #2: 0x39cef02c libsystem_c.dylib`abort + 76
    frame #3: 0x001f32ba [AppName]`uncaught_exception_handler + 26
    frame #4: 0x2f432184 CoreFoundation`__handleUncaughtException + 580
    frame #5: 0x3978e926 libobjc.A.dylib`_objc_terminate() + 174
    frame #6: 0x391541b2 libc++abi.dylib`std::__terminate(void (*)()) + 78
    frame #7: 0x39153d16 libc++abi.dylib`__cxa_rethrow + 102
    frame #8: 0x3978e80e libobjc.A.dylib`objc_exception_rethrow + 42
    frame #9: 0x36d7b150 UIFoundation`-[NSConcreteTextStorage addAttribute:value:range:] + 248
    frame #10: 0x337fc02e DataDetectorsUI`-[DDTextKitOperation _addResultsToAttributes] + 266
    frame #11: 0x337fc1d6 DataDetectorsUI`__46-[DDTextKitOperation doURLificationOnDocument]_block_invoke_2 + 26
    frame #12: 0x36d79a5e UIFoundation`-[NSTextStorage(ActorSupport) coordinateAccess:] + 34
    frame #13: 0x337fc1b8 DataDetectorsUI`__46-[DDTextKitOperation doURLificationOnDocument]_block_invoke + 116
    frame #14: 0x39c78bde libdispatch.dylib`_dispatch_barrier_sync_f_slow_invoke + 66
    frame #15: 0x39c730ae libdispatch.dylib`_dispatch_client_callout + 22
    frame #16: 0x39c759a8 libdispatch.dylib`_dispatch_main_queue_callback_4CF + 268
    frame #17: 0x2f3fc5b0 CoreFoundation`__CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__ + 8
    frame #18: 0x2f3fae7c CoreFoundation`__CFRunLoopRun + 1308
    frame #19: 0x2f365470 CoreFoundation`CFRunLoopRunSpecific + 524
    frame #20: 0x2f365252 CoreFoundation`CFRunLoopRunInMode + 106
    frame #21: 0x3409f2ea GraphicsServices`GSEventRunModal + 138
    frame #22: 0x31c1a844 UIKit`UIApplicationMain + 1136
  * frame #23: 0x000bffb4 [AppName]`main(argc=1, argv=0x27d4ecec) + 116 at main.m:16
(lldb) bt
* thread #22: tid = 0x2e57ea, 0x39da2cbc libsystem_pthread.dylib`start_wqthread, stop reason = signal SIGABRT
  * frame #0: 0x39da2cbc libsystem_pthread.dylib`start_wqthread

Here is where I set the attributed string:

// earlier in the code
tweetTextView.attributedText = [[NSAttributedString alloc] initWithString:tweetTextView.text];
...

-(void)findHashtagsAndAtMentionsInTweetText:(UITextView *)textView {

    NSString *tweetText = textView.text;

    NSError *error = nil;
    NSRegularExpression *regex = [NSRegularExpression regularExpressionWithPattern:@"(@(\\w+))|(^|\\W)(#|\\uFF03)(\\w*\\p{L}\\w*)" options:0 error:&error];
    NSArray *matches = [regex matchesInString:tweetText options:0 range:NSMakeRange(0, tweetText.length)];

    NSMutableAttributedString * myTagOrMention = [[NSMutableAttributedString alloc] initWithString:tweetTextView.text];

    for (NSTextCheckingResult *match in matches) {

        NSRange wordRange = [match rangeAtIndex:0]; // causing crash?
        NSString* word = [tweetText substringWithRange:wordRange];

        if([word rangeOfString:@"@"].location != NSNotFound) {

            // @ mention

            // remove whitespaces and @
            NSString *formattedTag = [NSString stringWithFormat:@"%@", [[word stringByReplacingOccurrencesOfString:@" " withString:@""] stringByReplacingOccurrencesOfString:@"@" withString:@""]];

            NSString *tweetContets = tweetTextView.text;
            NSRange range = [tweetContets rangeOfString:word];

            if([[UIApplication sharedApplication] canOpenURL:[NSURL URLWithString:@"twitter://"]]) {
                NSString *twitterAppURL = [NSString stringWithFormat:@"%@%@", @"twitter://user?screen_name=",formattedTag];
                [myTagOrMention addAttribute:NSLinkAttributeName value:twitterAppURL range:range];
            } else {

                [myTagOrMention addAttribute:NSLinkAttributeName value:[NSString stringWithFormat:@"%@%@", @"http://mobile.twitter.com/",formattedTag] range:range];
            }

            tweetTextView.attributedText = myTagOrMention;

        } else {
            // hashtag

            // remove whitespaces and pound
            NSString *formattedTag = [NSString stringWithFormat:@"%@", [[word stringByReplacingOccurrencesOfString:@" " withString:@""] stringByReplacingOccurrencesOfString:@"#" withString:@""]];

            NSString *tweetContets = tweetTextView.text;
            NSRange range = [tweetContets rangeOfString:word];

            [myTagOrMention addAttribute:NSLinkAttributeName value:[NSString stringWithFormat:@"%@%@%@%@", @"http://twitter.com/search/", @"?q=%23", formattedTag, @"&s=hash"] range:range];

            tweetTextView.attributedText = myTagOrMention;
        }
    }

Answer 1

The bug is not in the code you posted. The bug happens when a UITextView is reused while its links are still being generated, which is done asynchronously.

See these similar Stack Overflow questions:

• iOS 7 UITextView link detection crash in UITableView
• UITextViews in a UITableView link detection bug in iOS 7
• UITextView link detection in iOS 7

Many users have reported that setting the text view's text property to nil in the cell's prepareForReuse method resolves the issue. Alternatively you could use a library like TTTAttributedLabel instead of a text view.

The fact that it only appears on an iPhone 5C is probably a red herring. I bet this device is still running iOS 7, and the other devices have been updated to a newer version of iOS.

---

On a side note, there may be edge cases that your regex doesn't cover. I would delete your twitter parsing method and replace it with the official twitter-text-objc library.