iOS的一些小技巧

//info.plist中添加一个字段：view controller -base status bar 设置为NO 设置状态栏文字为白色
    
//有动画效果
[[UIApplication sharedApplication] setStatusBarStyle:UIStatusBarStyleLightContent animated:YES];

//无动画效果
[[UIApplication sharedApplication] setStatusBarStyle:UIStatusBarStyleLightContent];

UIView *statusBarView=[[UIView alloc] initWithFrame:CGRectMake(0, 0, 320, 20)];
    
statusBarView.backgroundColor=[UIColor blackColor];
    
[YouNav.view addSubview:statusBarView];
    
[[UIApplication sharedApplication] setStatusBarStyle:UIStatusBarStyleLightContent animated:NO];

 UITabBarController *tabVC = [[UITabBarController alloc] init];
    //获得tabbar
 UITabBar *tabBar = tabVC.tabBar;
    //设置透明度
  [tabBar setAlpha:0.8f];