NSString substringWithRange 崩溃
我有这样的代码：
- (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。我不明白这是怎么可能的，因为在 if 语句的条件下，charactersLeftAfterString 必然小于 0，所以charactersAvailableForString 总是小于字符串长度，那么范围怎么可能比字符串长度长呢？
I have this code:
- (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)
}
It's crashing on the sendString method, because of a bad NSRange. I don't understand how this is possible given charactersLeftAfterString is necessarily less than 0 given the condition of the if statement, so charactersAvailableForString is always less than the string length, so how can the range be longer than the string length?
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评论（2）
您是否使用过调试器并检查了
charactersAvailableForString的值？...还是打印出来的？
...或者查看崩溃时的值？
Have you used the debugger and checked the value of
charactersAvailableForString?... or printed it?
... or looked at the value when it crashes?
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 NSRange 异常，无论怎样，
charactersAvailableForString < 0
如果[字符串长度] = 5 且charactersLeftAfterString = -12，也会出现类似的问题。
字符串可用字符 = 5-12 = -7
[string substringWithRange:NSMakeRange(0,charactersAvailableForString)] 将给出 NsRange 异常。
If your string is empty, i.e [string length] = 0
[string substringWithRange:NSMakeRange(0, charactersAvailableForString)]
will always give a NSRange exception every time, no matter what as
charactersAvailableForString < 0
Also similar problems can arise if [string length] = 5 and charactersLeftAfterString = -12.
charactersAvailableForString = 5-12 = -7
[string substringWithRange:NSMakeRange(0, charactersAvailableForString)] will give NsRange Exception.