textViewDidChange: crashes in iOS 7 - objective-c

Question

As we know the UITextView is more powerful in iOS 7, but here it performs more fragile. The following code works fine when inputting "rr" with Chinese input keyboard in iOS 6, but crashes in iOS 7.
- (void)viewDidLoad
{
[super viewDidLoad];
self.tv = [[UITextView alloc] initWithFrame:CGRectMake(0, 100, 320, 100)];
self.tv.backgroundColor = [UIColor yellowColor];
self.tv.textColor = [UIColor blackColor];
self.tv.editable = YES;
self.tv.delegate = self;
[self.view addSubview:self.tv];
}
-(void)textViewDidChange:(UITextView *)textView{
int maxLength = 2;
if (self.tv.text.length > maxLength) {
NSLog(#"self.tv.text :%#",self.tv.text);
NSLog(#"self.tv.text.length :%d",self.tv.text.length);
NSLog(#"maxLength :%d",maxLength);
self.tv.text = [self.tv.text substringToIndex:maxLength];
}
}
The log is as following:
2013-11-13 15:48:16.003 Test2[1388:70b] self.tv.text :r r
2013-11-13 15:48:16.004 Test2[1388:70b] self.tv.text.length :3
2013-11-13 15:48:16.005 Test2[1388:70b] maxLength :2
2013-11-13 15:48:16.032 Test2[1388:70b] *** Terminating app due to uncaught exception 'NSRangeException', reason: 'NSMutableRLEArray replaceObjectsInRange:withObject:length:: Out of bounds'
*** First throw call stack:
(
0 CoreFoundation 0x017355e4 __exceptionPreprocess + 180
1 libobjc.A.dylib 0x014b88b6 objc_exception_throw + 44
2 CoreFoundation 0x017353bb +[NSException raise:format:] + 139
3 Foundation 0x010ebba1 -[NSMutableRLEArray replaceObjectsInRange:withObject:length:] + 136
4 Foundation 0x010ebb14 -[NSMutableRLEArray deleteObjectsInRange:] + 63
5 Foundation 0x010ea559 -[NSConcreteMutableAttributedString replaceCharactersInRange:withAttributedString:] + 324
6 UIFoundation 0x02d9d9f4 __71-[NSConcreteTextStorage replaceCharactersInRange:withAttributedString:]_block_invoke + 68
7 UIFoundation 0x02d9d92f -[NSConcreteTextStorage replaceCharactersInRange:withAttributedString:] + 121
8 UIKit 0x00924d22 __53-[UITextInputController setMarkedText:selectedRange:]_block_invoke + 352
9 UIFoundation 0x02d9b491 -[NSTextStorage coordinateEditing:] + 48
10 UIKit 0x00924a38 -[UITextInputController setMarkedText:selectedRange:] + 249
11 UIKit 0x008fb3b1 -[UITextView setMarkedText:selectedRange:] + 63
12 UIKit 0x00644aa5 -[UIResponder(UITextInput_Internal) _setMarkedText:selectedRange:] + 101
13 UIKit 0x004031aa -[UIKeyboardImpl setMarkedText:selectedRange:inputString:searchString:] + 365
14 UIKit 0x00419737 -[TIKeyboardOperationSetMarkedText(UIKeyboardImpl) main] + 178
15 Foundation 0x0118da69 -[__NSOperationInternal _start:] + 671
16 Foundation 0x0110a798 -[NSOperation start] + 83
17 UIKit 0x0040e08a -[UIKeyboardImpl updateCandidateDisplayAsyncWithCandidateSet:documentOperation:] + 188
18 UIKit 0x00419041 -[TIKeyboardOperationSetCandidates(UIKeyboardImpl) main] + 112
19 Foundation 0x0118da69 -[__NSOperationInternal _start:] + 671
20 Foundation 0x0110a798 -[NSOperation start] + 83
21 UIKit 0x0040671d -[UIKeyboardImpl performOperations:] + 153
22 UIKit 0x00404f4e -[UIKeyboardImpl continueGenerateCandidatesAsynchronouslyWithOperations:] + 40
23 UIKit 0x00404c51 __87-[UIKeyboardImpl replyHandlerForGenerateCandidatesAsynchronouslyWithSelectedCandidate:]_block_invoke_2 + 46
24 UIKit 0x009381b8 -[UIKeyboardTaskQueue continueExecutionOnMainThread] + 402
25 UIKit 0x0093885f -[UIKeyboardTaskQueue addTask:] + 144
26 CoreFoundation 0x01729d1d __invoking___ + 29
27 CoreFoundation 0x01729c2a -[NSInvocation invoke] + 362
28 UIKit 0x008e63d2 -[_UIActionWhenIdle invoke] + 100
29 UIKit 0x008e64a6 __41-[_UIActionWhenIdle addObserverToRunLoop]_block_invoke + 36
30 CoreFoundation 0x0172924d _runLoopObserverWithBlockContext + 29
31 CoreFoundation 0x016fd53e __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__ + 30
32 CoreFoundation 0x016fd48f __CFRunLoopDoObservers + 399
33 CoreFoundation 0x016db3b4 __CFRunLoopRun + 1076
34 CoreFoundation 0x016dab33 CFRunLoopRunSpecific + 467
35 CoreFoundation 0x016da94b CFRunLoopRunInMode + 123
36 GraphicsServices 0x036d69d7 GSEventRunModal + 192
37 GraphicsServices 0x036d67fe GSEventRun + 104
38 UIKit 0x0022b94b UIApplicationMain + 1225
39 Test2 0x0000388d main + 141
40 libdyld.dylib 0x01d7370d start + 1
41 ??? 0x00000001 0x0 + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException
In addition, I test the following code, it also crashes after input "rr" with Chinese input keyboard.
-(void)textViewDidChange:(UITextView *)textView{
int maxLength = 2;
if (self.tv.text.length > maxLength) {
self.tv.text = #"c";
}
}
Any help will be appreciated!

Answer 1

What's happening is that you're typing what is referred to as multistage text input, i.e. the input has to be confirmed from the user before it's actually committed into the underlying text. You get the crash because the text is only kind-of inputted, and until the text has been committed, it could easily change to something else.
To detect this situation, you're looking for the markedTextRange property of the UITextView, which indicates if you're in this complex input mode.
If the property is non-nil, then you're in this special input mode, so you should guard your modification code with something like:
if (self.tv.markedTextRange == nil && self.tv.text.length > maxLength) {
// Perform change
}
Near as I can tell the crash is triggered by the special multistage text input mode, so you should avoid changing the text while this mode is active.