iOS MMDrawerController 侧滑push问题

1.使用MMDrawer时push使用：

  DeviceViewController *device = [[DeviceViewController alloc] init];
  [self.navigationController pushViewController:device animated:YES];

如下图所示无法push，原始是self.navigationController是null.

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2.于是改成代码如下

DeviceViewController *device = [[DeviceViewController alloc] init];
RootTabController * tab  = (RootTabController*)self.mm_drawerController.centerViewController;
RootNavController *nav = tab.viewControllers[0];
[nav pushViewController:device animated:NO]; 
[self.mm_drawerController closeDrawerAnimated:YES completion:^(BOOL finished) {
     [self.mm_drawerController setOpenDrawerGestureModeMask:MMOpenDrawerGestureModeNone];
}];

会出现其他的tabbar无法Push.

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3.后来检查发现是因为nav的问题，将代码改成：

RootNavController *nav = tab.viewControllers[tab.selectedIndex];

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