creating UINavigationBar by code not works in iOS 14 beta 6

In my code, I create a UINavigationBar by code and add this to my view, like:

Code Block UINavigationBar *bar = [[UINavigationBar alloc] init];
bar.barTintColor = ...
[bar setBackgroundImage:... forBarMetrics:UIBarMetricsDefault]; 
[self.view addSubview:bar];

This works fine in iOS 13 and earlier version, but in iOS 14 beta version, all my settings of UINavigationBar not work and a UINavigationBar object is added to the view but all the necessary subviews of UINavigationBar such as UIBarBarkground and UINavigationBarContentView are gone.

To fix this problem, I change to init UINavigationBar form xib, but this way is more complicated and must keep a redundant xib file. So, please fix this bug in later iOS 14 version, Thanks.