textView:shouldChangeTextInRanges:replacementStrings: method crashes when NSTextStorage is edited - macos

Question

I'm new to Cocoa programming under OSX Lion, so this is a question I cannot find answer to.
I need to modify an attributed string which is entered by the user through the NSTextView.
Editing may include replacement of some portion(s) of the string inside the NSTextStorage and addition of NSTextAttachment objects.
I implemented the protocol and provided it for NSTextView instance as delegate.
I also implemented the method textView:shouldChangeTextInRanges:replacementStrings: in the next manner:
- (BOOL)textView:(NSTextView *)textView shouldChangeTextInRanges:(NSArray *)affectedRanges replacementStrings:(NSArray *)replacementStrings{
NSTextStorage* ts=[textView textStorage];
[ts beginEditing];
NSMutableString* buf=[ts mutableString];
//make some completions
NSRange rng;
rng.location=0;
rng.length=[buf length];
[buf replaceOccurrencesOfString:#"(." withString:#"(0." options:0 range:rng];
rng.location=0;
rng.length=[buf length];
[buf replaceOccurrencesOfString:#"-+" withString:#"-" options:0 range:rng];
rng.location=0;
rng.length=[buf length];
[buf replaceOccurrencesOfString:#"+-" withString:#"-" options:0 range:rng];
[ts endEditing];
return YES;
}
Thus I try the next scenario: when the application is up, the user types inside the NSTextView some text. If he types "(." everything is going well. But when he types "-+ " (minus, plus, whitespace) - the method crashes producing this dump:
[NSConcreteTextStorage attributesAtIndex:effectiveRange:]: Range or index out of bounds
(
0 CoreFoundation 0x00007fff95963286 __exceptionPreprocess + 198
1 libobjc.A.dylib 0x00007fff8c32bd5e objc_exception_throw + 43
2 CoreFoundation 0x00007fff959630ba +[NSException raise:format:arguments:] + 106
3 CoreFoundation 0x00007fff95963044 +[NSException raise:format:] + 116
4 AppKit 0x00007fff90acb5bd -[NSConcreteTextStorage attributesAtIndex:effectiveRange:] + 121
5 AppKit 0x00007fff90f4cde6 -[NSTextView insertText:replacementRange:] + 840
6 AppKit 0x00007fff910fc891 -[NSTextInputContext handleTSMEvent:] + 2289
7 AppKit 0x00007fff910fe4fe _NSTSMEventHandler + 165
8 HIToolbox 0x00007fff89745308 _ZL23DispatchEventToHandlersP14EventTargetRecP14OpaqueEventRefP14HandlerCallRec + 1263
9 HIToolbox 0x00007fff89744914 _ZL30SendEventToEventTargetInternalP14OpaqueEventRefP20OpaqueEventTargetRefP14HandlerCallRec + 446
10 HIToolbox 0x00007fff8975b6c7 SendEventToEventTarget + 76
11 HIToolbox 0x00007fff89930a4d SendTSMEvent + 35
12 HIToolbox 0x00007fff89930dd4 SendUnicodeTextAEToUnicodeDoc + 452
13 HIToolbox 0x00007fff8993095e TSMKeyEvent + 629
14 HIToolbox 0x00007fff8976f81a TSMProcessRawKeyEvent + 2350
15 AppKit 0x00007fff910fbade -[NSTextInputContext handleEvent:] + 639
16 AppKit 0x00007fff90fc7eaf -[NSView interpretKeyEvents:] + 248
17 AppKit 0x00007fff90f40c65 -[NSTextView keyDown:] + 691
18 AppKit 0x00007fff90a20544 -[NSWindow sendEvent:] + 7430
19 AppKit 0x00007fff909b868f -[NSApplication sendEvent:] + 5593
20 AppKit 0x00007fff9094e682 -[NSApplication run] + 555
21 AppKit 0x00007fff90bcd80c NSApplicationMain + 867
22 myapp 0x0000000100001302 main + 34
23 myapp 0x00000001000012d4 start + 52
It seems that shortened string causes some out-of-bounds spill.
What am I doing wrong and how can I fix this issue? Please help.

Answer 1

The -length method returns the quantity of characters in a NSString. The problem is that the first character is in the index 0. Try using [buf length] - 1. This should work.