iOS中关于UIWindow和statusbar的设置问题

- (UIStatusBarStyle)preferredStatusBarStyle​
- (void)setNeedsStatusBarAppearanceUpdate​

// TestView.h
#import
@interface TestView : UIView
@property (nonatomic, strong) NSString *clickTitle;​
- (void)show;
@end
// TestView.m
​#import "TestView.h"
@implementation TestView
{
  UIWindow *window;
  UIButton *clickBtn;
}
- (void)makeWindow
{
  window = [[UIWindow alloc] init];
  window.windowLevel = UIWindowLevelStatusBar + 1;
  window.backgroundColor = [UIColor clearColor];
  [window makeKeyAndVisible];
  TestVC *rootVC = [[TestVCalloc] init];
  rootVC.view.backgroundColor = [UIColorcolorWithRed:0green:0blue:0alpha:0.5];
  UINavigationController *navi = [[UINavigationControlleralloc]initWithRootViewController:rootVC];
  window.rootViewController = navi;
  navi.navigationBarHidden = YES;
  self.frame = CGRectMake(0, 0, window.frame.size.width - 40, 80);
  self.center = window.center;
  [rootVC.view addSubview:self];
}
- (instancetype)initWithFrame:(CGRect)frame
{
  if (self = [super initWithFrame:frame]) {
    clickBtn = [UIButton buttonWithType:UIButtonTypeCustom];
  }
  returnself;
}
- (NSString *)clickTitle
{
  if (!_clickTitle) {
    _clickTitle = @"clicks";
  }
  return_clickTitle;
}
- (void)show
{
  [clickBtn setTitle:self.clickTitleforState:UIControlStateNormal];
  [selfmakeWindow];
}
// TestVC.m
#import "TestVC.h"
@interfaceTestVC ()
@end
@implementation TestVC
- (void)viewDidLoad {
  [super viewDidLoad];
  // Do any additional setup after loading the view.
  [self setNeedsStatusBarAppearanceUpdate];
}
- (UIStatusBarStyle)preferredStatusBarStyle
{
  return UIStatusBarStyleLightContent;
}