IOS中限制TextField中输入的类型以及长度

-(BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string{
   // Check for non-numeric characters
   NSUInteger lengthOfString = string.length;
   for (NSInteger loopIndex = 0; loopIndex < lengthOfString; loopIndex++) {//只允许数字输入
       unichar character = [string characterAtIndex:loopIndex];
       if (character < 48) return NO; // 48 unichar for 0
       if (character > 57) return NO; // 57 unichar for 9
   }
   // Check for total length
   NSUInteger proposedNewLength = textField.text.length - range.length + string.length;
   if (proposedNewLength > 3) return NO;//限制长度
   return YES;
   }