• 银行卡每4位，添加一个空格进行分割

-(BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string{
if (self.bankNumTextFeild==textField) {
        
        NSString *text = [self.bankNumTextFeild 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:@""];
        
        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]];
        
        // 限制长度
        if (newString.length >= 24) {
            return NO;
        }
        
        [self.bankNumTextFeild setText:newString];
        
        return NO;
    }
    
   
    return YES;
}