在輸入東西的時候，如果想限制最大字數，可以用下面方法：

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string

{

    if ([string isEqualToString:@"\n"]){

        return YES;

    }

   
    NSString * aString = [textField.text stringByReplacingCharactersInRange:range withString:string];

    if (self.searchTextField == textField)

    {

        if ([aString length] > 5) {

            textField.text = [aString substringToIndex:5];           

            UIAlertView *alert = [[UIAlertView alloc] initWithTitle:nil

                                                             message:@"超過最大字數不能輸入了"

                                                            delegate:nil

                                                   cancelButtonTitle:@"Ok"

                                                   otherButtonTitles:nil, nil];

            [alert show];

            [alert release];

            return NO;

        }

    }

    return YES;

 

}