NSMutableArray *array = [[NSMutableArray alloc]initWithArray: [self.navigationController viewControllers]];

 //  删除栈中的一个viewcontroller

    [array removeObjectAtIndex:];

//  清掉栈中的所有viewcontroller并跳到指定viewcontroller

   [array removeAllObjects];

    pxViewController *px = [[pxViewController alloc]init];

    [array addObject:px];

    [px release];

    self.navigationController.viewControllers = array;