使用NSMakeRange的子串超出边界异常

Question

循环时,在a中生成每个字母的子字符串,NSString抛出此异常:

-[__NSCFString substringWithRange:]: Range or index out of bounds

码:

- (void) analyzeContent:(NSString *)content
{
    content = [content uppercaseString];
    for (int i = 1; i < content.length; i++) {
        NSString *ch = [content substringWithRange:NSMakeRange(i-1, i)]; // <-- exception
    }
}

来自这里:

- (IBAction)analyze:(id)sender
{
    if (!self.text) {
        NSString *path = [[NSBundle mainBundle] pathForResource:CYPHERTEXT_FILE
                                                         ofType:@"txt"];
        self.text = [NSString stringWithContentsOfFile:path
                                              encoding:NSUTF8StringEncoding
                                                 error:NULL];
    }

    [self.progIndicator setHidden:NO];
    [self.progIndicator startAnimation:nil];
    dispatch_queue_t queue = dispatch_queue_create("queue", 0);
    dispatch_async(queue, ^{

        [self.analyzer analyzeContent:self.text];

        // When finished update UI
        dispatch_sync(dispatch_get_main_queue(), ^{
            [self.progIndicator setHidden:YES];
            [self.progIndicator stopAnimation:nil];
        });
    });
}

text- 属性声明是: @property (copy) NSString *text;

i = 13172和时抛出异常content.length = 26344.

代码在后台线程中运行,但content不被任何其他线程访问.

感谢您的任何帮助!

Answer 1

问题是:

我虽然NSMakeRange参数index-from和index-to.它实际上需要从子串的索引和长度,所以当迭代通过中间标记(见问题)时,它超出了界限.

愚蠢...