addChildViewController ipad 中Controller的嵌套和叠加

1.addChildViewController 在 base controller中添加子的controller，会自动调用子的controller中viewDidload，viewWillAppear等视图方法，可以完成一个controller叠加各种视图

2.base 的controller必须是UIViewController，如果是 UINavigationController,则没法控制子controller frame的大小

示例代码：

    BaseNavController * nav = [[BaseNavController alloc] initWithRootViewController:agendaController];

    nav.view.autoresizingMask = UIViewAutoresizingNone;

    [nav.view addGestureRecognizer:[[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(dragView:)]];

    [self addChildViewController:nav];

    nav.view.frame =  CGRectMake(270, -20, DeviceWidth - 270, DeviceHeight - 200);//homeViewLeftMenuViewWidth

    nav.view.backgroundColor = [UIColor yellowColor];

    [self.view addSubview:nav.view];