如上图所示，如何装载Storyboard中指定的ViewController?
首先，需要指定ViewController的ID，如上图右上方红色方框内的Storyboard ID。然后使用下面的代码：
- UIStoryboard* mainStoryboard = [UIStoryboard storyboardWithName:@"MainStoryboard_iPhone" bundle:nil];
- LeftViewController *leftController = [mainStoryboard instantiateViewControllerWithIdentifier:@"leftViewController"];
或者使用下面的代码：
- UIStoryboard* mainStoryboard = [UIStoryboard storyboardWithName:@"MainStoryboard_iPhone" bundle:nil];
- ViewController *leftController = [mainStoryboard instantiateViewControllerWithIdentifier:@"leftViewController"];
- UINavigationController *navController = [[UINavigationController alloc] initWithRootViewController:leftController];
