類名 ()<UITextFieldDelegate>self.textField.delegate = self;

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string{  if (textField == self.contentTextField) {    // 4位分隔銀行卡卡號    NSString *text = [textField text];    NSCharacterSet *characterSet = [NSCharacterSet characterSetWithCharactersInString:@"0123456789/b"];    string = [string stringByReplacingOccurrencesOfString:@" " withString:@""];    if ([string rangeOfCharacterFromSet:[characterSet invertedSet]].location != NSNotFound) {      return NO;    }    text = [text stringByReplacingCharactersInRange:range withString:string];    text = [text stringByReplacingOccurrencesOfString:@" " withString:@""];    NSLog(@"%@",text);//    text為輸入框內的文本，沒有“ ”的內容    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]];    if ([newString stringByReplacingOccurrencesOfString:@" " withString:@""].length >= 21) {      return NO;    }    [textField setText:newString];    return NO;  }  return YES;}