ios銀行卡號加入* 並四個一個空格

+(NSString *)getNewBankNumWitOldBankNum:(NSString *)bankNum
{
    NSMutableString *mutableStr;
    if (bankNum.length) {
    mutableStr = [NSMutableString stringWithString:bankNum];
    for (int i = 0 ; i < mutableStr.length; i ++) {
        if (i>2&&i<mutableStr.length - 3) {
            [mutableStr replaceCharactersInRange:NSMakeRange(i, 1) withString:@"*"];
        }
    }
        NSString *text = mutableStr;
        NSCharacterSet *characterSet = [NSCharacterSet characterSetWithCharactersInString:@"0123456789\b"];
        text = [text stringByReplacingOccurrencesOfString:@" " withString:@""];
        NSString *newString = @"";
        while (text.length > 0) {
            NSString *subString = [text substringToIndex:MIN(text.length, 4)];
            newString = [newString stringByAppendingString:subString];
            if (subString.length == 4) {
                newString = [newString stringByAppendingString:@" "];
            }
            text = [text substringFromIndex:MIN(text.length, 4)];
        }
        newString = [newString stringByTrimmingCharactersInSet:[characterSet invertedSet]];
    return newString;
    }
    return bankNum;
    
}