应用第一次启动，修改rootViewController方法

1、第一次设置

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2、修改rootViewController
        AppDelegate *delegate = (AppDelegate *)[[UIApplication sharedApplication] delegate];    // 在delegate中初始化新的controller    [delegate initTabbarController];    // 修改rootViewController    [delegate.window addSubview:delegate.tabbarController.view];    [self.view removeFromSuperview];        delegate.window.rootViewController = delegate.tabbarController;
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