iOS UITextField 显示银行卡格式

类名 ()<UITextFieldDelegate>

self.textField.delegate = self;

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
{
   if (textField == self.contentTextField) {
       // 4位分隔银行卡卡号
       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为输入框内的文本，没有“ ”的内容       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;
}