导航栏的效果一些变化

 //导航条背景图
    [[UINavigationBar appearance] setBackgroundImage:[UIImage imageNamed:@"navigationItem_background"] forBarPosition:UIBarPositionAny barMetrics:UIBarMetricsDefault];
    //导航条的文字的颜色
    self.navigationController.navigationBar.titleTextAttributes = @{NSForegroundColorAttributeName:[UIColor whiteColor]};