ViewPager on back stack calls Presenter's method detachView(retainInstance=true)

[Thomas-Vos]

Hi Hannes,

I'm having some issues with a ViewPager in the back stack.

Mosby Version:
mvp-common:3.0.4 and viewstate:3.0.4

Expected behavior
I have a Fragment called A that contains a ViewPager that contains Fragments B and C. When Fragment A is put on the back stack, the method detachView(retainInstance=false) gets called. At the same time, detachView(retainInstance=false) is supposed to be called for Fragments B and C.

Actual behavior (include a stacktrace if crash)
When Fragment A is put on the back stack, the following happens:

• Fragment A Presenter: detachView(retainInstance=false)
• Fragment B Presenter: detachView(retainInstance=true)
• Fragment C Presenter: detachView(retainInstance=true)

As you can see, retainInstance is true for both B and C, but it should be false.

Steps to reproduce the behavior or link to a sample repository

1. Create Fragment A containing a ViewPager that contains Fragments B and C.
2. All Fragments call setRetainInstance(true) in the onCreate() method.
3. The MVP delegate is instantiated like this: new FragmentMvpViewStateDelegateImpl<>(this, this, true, false);.
4. Now put Fragment A on the backstack and see what happens.

Thanks, Thomas

[sockeqwe]

Hey,
I see ... This bug seems to occur if you have setRetainInstance(true) and `new FragmentMvpViewStateDelegateImpl<>(..., keepPresenterAndViewStateOnBackstack = false)´ so you don't want to keep the presenter.

Beside that this is a bug (thanks for reporting),
what is actually the reason behind using setRetainInstance(true) in that case? Does it work as expected with setRetainInstance(false)?

[Thomas-Vos]

Hello @sockeqwe, I want to keep the presenter on a configuration change, that's why I call setRetainInstance(true). I just tried without calling setRetainInstance(true); the presenter is not retained anymore on a configuration change, and I'm still having the same issue.

If I return to Fragment A (by pressing back or popping the back stack), the presenter is recreated anyway, so that's why I set keepPresenterAndViewStateOnBackstack to false. (issue #265)

I also noticed if you remove Fragment A from the back stack (go "up"), then Fragment B/C call detachView(retainInstance=true). I currently have worked around this by calling detachView(false) manually in the Fragment's onDestroy(). Is this a bug?

Thanks for your help,
Thomas

[sockeqwe]

See #274. Feel free to reopen this issue if 3.1.0 (snapshot) doesn't solve this porblem.