UINavigationBar更改默认样式

• 改NavigationBar的颜色，UIAppearance里面改TintColor而不是backgroundColor
  [[UINavigationBar appearance] setBarTintColor:[UIColor blackColor]];

• 改NavigationItem的颜色，
  self.navigationController.navigationBar.tintColor = [UIColor greenColor];
  OR
  self.window.tintColor = [UIColor redColor]
  第二种同时修改navigationitem和tabbaritem的选中颜色

• 改NavigationBar Title的颜色，
  [[UINavigationBar appearance]setTitleTextAttributes:@{NSForegroundColorAttributeName:[UIColor whiteColor]}];
self.navigationController?.navigationBar.titleTextAttributes = [NSForegroundColorAttributeName:UIColor.whiteColor()]

• 让backbutton title消失
  [[UIBarButtonItem appearance] setBackButtonTitlePositionAdjustment:UIOffsetMake(0, -60) forBarMetrics:UIBarMetricsDefault];