iOS如何截取字符串中某个字符出现第N次时的字符串

举例：

NSString *str = @"DISTRICT-00001-00001-00005-00020";

如何将上述字符串的第三个"-"前内容截取出来？

一、这种最常见的做法是将字符串分割然后拼接如下：

NSString *str = @"DISTRICT-00001-00001-00005-00020";
    NSArray *arr = [str componentsSeparatedByString:@"-"];
    NSString *newStr = [NSString stringWithFormat:@"%@-%@-%@",arr[0],arr[1],arr[2]];
    NSLog(@"%@====%@",arr,newStr);

结果如下：

2018-06-14 12:13:08.494293+0800 test[9145:1108895] (
    DISTRICT,
    00001,
    00001,
    00005,
    00020
)====DISTRICT-00001-00001

这样做就比较繁琐一点，而且假如字符串比较长，这样的方法就不是很方便了

二、先遍历字符串找到所有的@"-"所在的位置的index，然后通过index将字符串进行截取。具体方法如下：

- (NSMutableArray *)getRangeStr:(NSString *)text findText:(NSString *)findText{
    NSMutableArray *arrayRanges = [NSMutableArray arrayWithCapacity:3];
    if (findText == nil && [findText isEqualToString:@""]){
        return nil;
    }
    NSRange rang = [text rangeOfString:findText]; //获取第一次出现的range
    if (rang.location != NSNotFound && rang.length != 0){
        [arrayRanges addObject:[NSNumber numberWithInteger:rang.location]];//将第一次的加入到数组中
        NSRange rang1 = {0,0};
        NSInteger location = 0;
        NSInteger length = 0;
        for (int i = 0;; i++){
            if (0 == i){
                location = rang.location + rang.length;
                length = text.length - rang.location - rang.length;
                rang1 = NSMakeRange(location, length);
            }else{
                location = rang1.location + rang1.length;
                length = text.length - rang1.location - rang1.length;
                rang1 = NSMakeRange(location, length);
            }
            //在一个range范围内查找另一个字符串的range
            rang1 = [text rangeOfString:findText options:NSCaseInsensitiveSearch range:rang1];
            if (rang1.location == NSNotFound && rang1.length == 0){
                break;
            }
            else{
                //添加符合条件的location进数组
                [arrayRanges addObject:[NSNumber numberWithInteger:rang1.location]];
            }
        }
        return arrayRanges;
    }
    return nil;
}

NSMutableArray *array = [self getRangeStr:str findText:@"-"];
    NSLog(@"array:%@",array);
    NSString *newString = [str substringToIndex:20];
    NSLog(@"newString:%@",newString);

结果如下：

2018-06-14 12:34:30.102458+0800 test[9233:1119637] array:(
    8,
    14,
    20,
    26
)
2018-06-14 12:34:30.102480+0800 test[9233:1119637] newString:DISTRICT-00001-00001