How to make a uiactionsheet dismiss when you tap outside eg above it?

How do i make a uiactionsheet dismiss when you tap outside eg above it? This is for iPhone. Apparently the ipad does this by default (I may be wrong).

Ok got a solution. The following applies to a subclass of a UIActionSheet

// For detecting taps outside of the alert view
-(void)tapOut:(UIGestureRecognizer *)gestureRecognizer {
    CGPoint p = [gestureRecognizer locationInView:self];
    if (p.y < 0) { // They tapped outside
        [self dismissWithClickedButtonIndex:0 animated:YES];
    }
}

-(void) showFromTabBar:(UITabBar *)view {
    [super showFromTabBar:view];

    // Capture taps outside the bounds of this alert view
    UITapGestureRecognizer *tap = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(tapOut:)];
    tap.cancelsTouchesInView = NO; // So that legit taps on the table bubble up to the tableview
    [self.superview addGestureRecognizer:tap];
    [tap release];
}

The gist of it is to add a gesture recogniser to the action sheet's superview, and test all taps to see if they are above the action sheet.