Carousel resets position to head when using Navigation Component

[shawnlinboy]

Preconditions

• Epoxy 5.1.3
• Navigation Component 2.7.5

Test

• ./gradlew installDebug
• Scroll list item to a random postion, click Next to SecondFragment, and then back.
• The carousel list resets to head position.

I wrote a demo to elaborate this issue, see: https://github.com/shawnlinboy/epoxy-carousel-issue/tree/master

[viroth-ty]

Navigation component using fragment as views, so in order to save state you need to :

private val controller: YourController by lazy {
    YourController()
}

override fun onSaveInstanceState(outState: Bundle) {
    super.onSaveInstanceState(outState)
    controller.onSaveInstanceState(outState)
}
override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    controller.onRestoreInstanceState(savedInstanceState)
}

Store data in ViewModel with Live data or using mavericks

[shawnlinboy]

Navigation component using fragment as views, so in order to save state you need to :

private val controller: YourController by lazy {
    YourController()
}

override fun onSaveInstanceState(outState: Bundle) {
    super.onSaveInstanceState(outState)
    controller.onSaveInstanceState(outState)
}
override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    controller.onRestoreInstanceState(savedInstanceState)
}

Store data in ViewModel with Live data or using mavericks

Well, I think I've solve this issue now, thanks for the inspiration!

The detail was that navigating throngh fragments with Navigation component did not trigger source fragment's onSaveInstanceState(Bundle) except the fragment's host activity calls its own onSaveInstanceState(Bundle)(Ref), this condition is so harsh like it tends to only happen when the screen is rotated or so. However, I got inspired by migrating the "save and restore combo" from fragment's onSaveInstanceState and onCreate to onDestroyView and onViewCreated, and it works. :)

I've uploaded this workaround to this CL, and hope it helps others.