Switching between dark and light mode while the app is open confuses the appearance

[designsimply]

Steps to reproduce:

1. Open any area of the app.
2. Put the app in the background (do not force close).
3. On the device, go to Settings > Display & Brightness > Appearance.
4. Change the mode from Light to Dark or vice versa.
5. Go back to the app and observe that some parts of the app change and others do not.
6. Force refresh the app.
7. Repeat steps 1-5.

Result: if the appearance is switched from Dark to Light or from Light to Dark after the app is opened, the colors become confused. (40s)

^{Tested with WPiOS 13.2-beta1 (TestFlight) on iPhone 6S iOS 13.1 Beta 1 in Dark & Light Modes.}

The view controller needs to listen for the notification that the mode has changed and refresh the UI.

^{h/t @rachelmcr for the original report at p5T066-Zv-p2#comment-3427 and @jkmassel for the tip.}

[designsimply]

I tested this again as part of 13.4 beta testing and found that if you toggle dark mode while the screen is visible the text color still doesn't update for the login/signup, log in, and logged in as screens.

Steps to reproduce:

1. Log out.
2. Tap "Log In".
3. Go to iOS Settings > Display & Brightness > Appearance.
4. Switch from Light to Dark (or vice versa).
5. Go back to the WP app and check to see if the buttons on the log in screen look correct.
6. Close and re-open the app.
7. Repeat steps 3-6 for the "Log In/ Sign up" screen.
8. Repeat steps 3-6 for the "Logged in as" screen.

Result: the buttons become unreadable with dark text on a dark background or light text on a light background if you toggle dark mode for the login/signup, log in, and logged in as screens screens while the app is open.

^{Tested with WPiOS 13.4.0.1 (TestFlight) on iPhone 6S iOS 13.2.}

[designsimply]

1. Start in Dark Mode.
2. Open Reader and like some posts.
3. Switch to Light Mode.
4. Open Reader again and like some posts.

Result: the icons at the bottom of the post become very light gray on white and are hard to see.

^{(Left) After switching from dark to light while the app is open and (right) after closing and reopening the app while in light mode, tested with WP Internal 13.5.20191021 (HockeyApp) on iPhone 6S iOS 13.2.}

[designsimply]

I tested with WP Internal 13.6.20111104 and I can still see the problem happening where switching from dark to light mode, or vice versa, causes some buttons to become unreadable. (13s)

^{Tested with WP Internal 13.6.20111104 (HockeyApp version) on iPhone 6S iOS 13.2.}

@danielebogo do you think you could fix this for the 13.6 or 13.7 release?

[danielebogo]

@designsimply this is basically the main task for Dark Mode V2. There's a list of elements you can see in the project card that have the same problem. Probably some can be addressed in 13.7? @frosty

[designsimply]

Possibly related: #13364.