UIAlertView 自动dismiss? (先设NSTimer，后调用Delegate)

- (void) performDismiss: (NSTimer *)timer

{
    [baseAlert dismissWithClickedButtonIndex:0 animated: NO ]; //important
    [baseAlert release];
    baseAlert = NULL ;
}

- ( void ) presentSheet
{
    baseAlert = [[UIAlertView alloc]
                              initWithTitle:@ "Alert" message:@ "\nMessage to user with asynchronous information"
                              delegate: self cancelButtonTitle: nil
                              otherButtonTitles: nil ];
    [ NSTimer scheduledTimerWithTimeInterval:1.0f target: self selector : @selector (performDismiss:)
                                   userInfo: nil repeats: NO ];
    [baseAlert show];
}