How to show double height green statusbar (In-Call) in foreground app on device?

Question

There's a lot of questions here asking for displaying a red recording bar while in background. It's totally clear I should use AVAudioSession category AVAudioSessionCategoryPlayAndRecord for that. My question is how can I display a green In-Call bar (or at least red bar) in a foreground app when having an active VOIP call in my app? So I could return to call UI tapping a statusbar area, just like Whatsapp or Skype does.

What I've already tried:

• voip and audio modes in UIBackgroundModes key in Info.plist + setCategory:AVAudioSessionCategoryPlayAndRecord + setActive as suggested in this SO answer (gives me a red statusbar when going background, but nothing while in foreground)
• Previous + AVAudioSession + setMode:AVAudioSessionModeVoiceChat - didn't work
• Set kCFStreamNetworkServiceTypeVoIP flag to socket in pjsip sources and recompiled it - didn't help. Also, deprecated since iOS 8.
• Created a separate socket, set the voip flag for inputStream/outputStream: [self.inputStream setProperty:NSStreamNetworkServiceTypeVoIP forKey:NSStreamNetworkServiceType] (took the sample code from here)

Using pjsip for calls. What else can I try to increase a statusbar height, moving all the UI down? Are there any standard ways to do that, or I should hack it my own by resizing a root UIWindow and setting another green UIWindow under the statusbar?

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Edit: Since no answer is found for a standard way to do that, accepted @roman-ermolov answer. For those who will search for an answer I may suggest several options to do it yourself:

1. Wrap your root viewcontroller inside container, like in Apple's iAdSuite with Storyboards example. Take a look at my sample project for example. Probably the best way to make that bar.
2. Hack UINavigationBar height (see this approach) - doesn't work for landscape yet, but may probably be solved
3. Control your main UIWindow's frame yourself, place another UIWindow under the statusbar with the desired content.

Answer 1

I have made an investigation of both apps (WhatsApp & Skype) and learned that they used their own UIView for achieving this functionality.

This is Skype:

This is WhatsApp (Reveal can't get real snapshot, but it transmits basic idea):

In both apps it is a UIView which starts on top of the screen and several methods for format output text / handle touch on it.

In iOS 10 Apple introduced CallKit.framework, but it seems that it has not that kind of functionality too, so the only way to do it - do it yourself.

Answer 2

Roman Ermolov's answer explained that some apps use their own UIView for this functionality, but does not explain how. The way I see it, you have a few options.

If you want to lay the view on top of (and covering) the current view controller, you could create a UIView with a UILabel or your own UIWindow and add that as a subview of your applications' keyWindow.

To have the view stick on top without covering the contents of the view controller, you could take the same approach as above and manually resize the application window or window's root view controller when you add the call bar subview. Alternatively, you could create a UIViewController base class which contains this call bar subview and an outlet for the view's height constraint. The default value of this constraint should be zero. Then, when a call is placed, change the height constraint to your desired call back height. This constraint approach might work on the application's UIWindow as well, but I'm not too familiar with using constraints on an application's window.