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;  
   }