bug: Trying to enter Login screen twice crashes the app

[haroldadmin]

Describe the bug
Trying to enter Login screen twice crashes the app

To Reproduce

1. Go to Login page
2. Tap on Login in Bottom Nav again
3. App crashes

Expected behavior
App does not crash

Screenshots

Crash log

2019-03-07 19:27:46.601 31803-31803/com.eventyay.attendee E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.eventyay.attendee, PID: 31803
    java.lang.IllegalStateException: Fragment LoginFragment{3bfb136 (8835c986-94ef-4728-ac33-e6a256da19f0) id=0x7f0800f4} has null arguments
        at org.fossasia.openevent.general.auth.LoginFragment$$special$$inlined$navArgs$1.invoke(FragmentNavArgsLazy.kt:42)
        at org.fossasia.openevent.general.auth.LoginFragment$$special$$inlined$navArgs$1.invoke(Unknown Source:0)
        at androidx.navigation.NavArgsLazy.getValue(NavArgsLazy.kt:44)
        at androidx.navigation.NavArgsLazy.getValue(NavArgsLazy.kt:34)
        at org.fossasia.openevent.general.auth.LoginFragment.getSafeArgs(Unknown Source:28)
        at org.fossasia.openevent.general.auth.LoginFragment.showSnackbar(LoginFragment.kt:214)
        at org.fossasia.openevent.general.auth.LoginFragment.onCreateView(LoginFragment.kt:60)
        at androidx.fragment.app.Fragment.performCreateView(Fragment.java:2530)
        at androidx.fragment.app.FragmentManagerImpl.moveToState(FragmentManagerImpl.java:887)
        at androidx.fragment.app.FragmentManagerImpl.addAddedFragments(FragmentManagerImpl.java:2090)
        at androidx.fragment.app.FragmentManagerImpl.executeOpsTogether(FragmentManagerImpl.java:1864)
        at androidx.fragment.app.FragmentManagerImpl.removeRedundantOperationsAndExecute(FragmentManagerImpl.java:1820)
        at androidx.fragment.app.FragmentManagerImpl.execPendingActions(FragmentManagerImpl.java:1721)
        at androidx.fragment.app.FragmentManagerImpl$1.run(FragmentManagerImpl.java:147)
        at android.os.Handler.handleCallback(Handler.java:873)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:193)
        at android.app.ActivityThread.main(ActivityThread.java:6718)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)

Smartphone Info:

Device: Google Pixel
OS: Android 9 Pie

Would you like to work on the issue?
Yes

[ShridharGoel]

Not able to reproduce the issue. Can you attach logs?

[haroldadmin]

@ShridharGoel I have updated the issue with crash logs.

The problem occurs because of Navigation AAC:

1. It tries to replace the existing fragment with the one selected in bottom nav, even if they are the same fragment.
2. When it instantiates this same fragment again, it does not pass the arguments given to the previous instance to this new instance.

I am going to work on a fix for this and send a PR soon.

[ShridharGoel]

Yes, reproduced after pulling the latest commits. Go ahead.

[RotBolt]

@haroldadmin, uhh there is No PR till now, I am almost done with this issue . Could I proceed ?

[haroldadmin]

Um sure. My exams are going on till the end of the week, you can take up the issue if you want. What approach have you used to solve this, btw?

[RotBolt]

safeArgs currently throw Execption when are null ,
But in the nav_graph.xml , in fragment -> in argument , default value is given null , app type is also set null . This is what throwing exception .

[haroldadmin]

I was thinking the exception is thrown when the fragment is instantiated without any arguments, such as when pressing the login tab in the bottom nav view. I might be wrong, though. Cool, send your PR and I'll help review it if I get the chance.

[RotBolt]

By NavLazyArgs , now setting arguments comes under the control of it. Setting null to it causes Throw execption.

@MainThread
inline fun <reified Args : NavArgs> Fragment.navArgs() = NavArgsLazy(Args::class) {
    arguments ?: throw IllegalStateException("Fragment $this has null arguments")
}

Thats from its code

[haroldadmin]

You'd notice that it checks if the arguments property on the receiver (Fragment) is null or not. If it is not null, it parses it otherwise it throws an exception. This means that it doesn't care if the value of the variables inside the bundle is null. It only cares if the bundle itself is null. I maybe completely off-base here, though.

[RotBolt]

You are right about arguments , but if you set default value of argument null then safeArgs Param itself become null . Thus throws Exception

[haroldadmin]

Oh. Okay. That makes sense. This is a very weird issue with the Nav AAC then. If the arguments bundle contains args with null values, then pass me an arg bundle with null values! Don't pass me a null bundle. This combined with the fact that the navArgs() delegate throws an exception when args are null makes for a very poorly laid out design.

[RotBolt]

@haroldadmin I have made PR, you could review it now :)