例：將下列字串中方括號[]中的內容提取出來並形成一個Array：

NSString* entry = @"[field1] [field2] [field3] [field4] [field5]";

解法一：使用componentsSeparatedByString:方法分解：

    NSArray *rawFields = [entry componentsSeparatedByString:@"] ["];
    NSMutableArray *fields = [NSMutableArray arrayWithArray:rawFields];

    //Remove '[' from the first field
 

    NSString* firstRawField = [rawFields[0] stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceCharacterSet]];
    if([firstRawField hasPrefix:@"["] && [firstRawField length] > 1){
        [fields replaceObjectAtIndex:0 withObject:[firstRawField substringFromIndex:1]];
    }

    //Remove ']' from the last field
 

    NSString* lastRawField = [rawFields[rawFields.count - 1] stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceCharacterSet]];
    if([lastRawField hasSuffix:@"]"] && [lastRawField length] > 1){
        [fields replaceObjectAtIndex:(rawFields.count - 1) withObject:[lastRawField substringToIndex:[lastRawField length] - 1
 
]];
    }

解法二：使用正則表示式分解：

    __block NSMutableArray *fields = [[NSMutableArray alloc] init];
    NSError *error = NULL;
    NSRegularExpression *fieldRegularExpression = [NSRegularExpression
                                                         regularExpressionWithPattern:@"\\[[^\\]]*\\]"
                                                         options:NSRegularExpressionCaseInsensitive
                                                         error:&error];
    [fieldRegularExpression enumerateMatchesInString:entry options:0 range:NSMakeRange(0, [entry length]) 
    usingBlock:^(NSTextCheckingResult *match, NSMatchingFlags flags, BOOL *stop){
        if(match.range.length > 2) {
            NSRange range = NSMakeRange(match.range.location + 1, match.range.length - 2);  //Remove '[' and ']'
            [fields insertObject:[entry substringWithRange:range] atIndex:fields.count];
        } else {
            [fields insertObject:EMPTY_STRING atIndex:fields.count];
        }

    }];

這裡，正則表示式

@"\\[[^\\]]*\\]"

的意義為左右方括號中包含任意長度的字串，且字串不含右方括號’]’。
複習：正則表示式中，’\’代表轉義字元，’[^list]’代表不含的字符集，’*’代表重複0到無窮多個前一個字元。