NSString substringWithRange崩溃

Question

我有这段代码：

- (void)splitAndSendString:(NSString *)string
             withAlignment:(UITextAlignment)alignment
         verticalExpansion:(NSUInteger)verticalExpansion
       horizontalExpansion:(NSUInteger)horizontalExpansion
                     inRed:(BOOL)isRed
          leftBumperString:(NSString *)leftString
         rightBumperString:(NSString *)rightString
                lineLength:(NSUInteger)lineLength
{
    NSInteger charactersLeftAfterString = lineLength - [string length] -
            [leftString length] - [rightString length];

   // if either of the bumpers is nil, then replace it with @""
   //so that we don't get "null" printed
   if (leftString == nil)  { leftString = @"";     }
   if (rightString == nil) { rightString = @"";    }

   if (charactersLeftAfterString < 0) {
        NSInteger charactersAvailableForString =
           [string length] + charactersLeftAfterString;
        [self sendString:[NSString stringWithFormat:@"%@%@%@", leftString, [string substringWithRange:NSMakeRange(0, charactersAvailableForString)], rightString] withAlignment:UITextAlignmentLeft verticalExpansion:verticalExpansion horizontalExpansion:horizontalExpansion inRed:isRed];
   }
   //(a lot of other code here that isn't relevant)
}

由于NSRange错误，它在sendString方法上崩溃了。我不明白如果给定if语句的条件，由于charactersLeftAfterString必须小于0，所以这是可能的，所以charactersAvailableForString总是小于字符串长度，那么范围如何比字符串长度长？

Answer 1

您是否使用过调试器并检查了charactersAvailableForString？

的值

......还是打印出来的？

...或者看崩溃时的值？

Answer 2

如果你的字符串是空的，即[string length] = 0

[string substringWithRange：NSMakeRange（0，charactersAvailableForString）]

每次都会给出一个NSRange异常，无论是什么

charactersAvailableForString＆lt; 0

如果[string length] = 5且charactersLeftAfterString = -12，也会出现类似的问题。 charactersAvailableForString = 5-12 = -7 [string substringWithRange：NSMakeRange（0，charactersAvailableForString）]将给出NsRange异常。