Develop Reference

Android Navigation Graph not displaying start fragment

I'm running into a wall debugging what should be a simple issue: I have an app with one activity, which contains a navigation graph, which should display a fragment on start. But it isn't.
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<FrameLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity"
>
<androidx.fragment.app.FragmentContainerView
android:id="#+id/nav_host_fragment"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:defaultNavHost="true"
app:navGraph="#navigation/nav_graph"/>
</FrameLayout>
res/navigation/nav_graph.xml
<?xml version="1.0" encoding="utf-8"?>
<navigation xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="#+id/nav_graph"
app:startDestination="#id/listFragment"
>
<fragment
android:id="#+id/listFragment"
android:name="org.example.my_app.ui.ListFragment"
android:label="fragment_list"
tools:layout="#layout/fragment_list"
>
<action
android:id="#+id/action_listFragment_to_detailFragment"
app:destination="#id/detailFragment"
/>
</fragment>
<fragment
android:id="#+id/detailFragment"
android:name="org.example.my_app.ui.DetailFragment"
android:label="fragment_detail"
tools:layout="#layout/fragment_detail"
/>
</navigation>
fragment_list.xml
<?xml version="1.0" encoding="utf-8"?>
<FrameLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".ui.ListFragment"
>
<TextView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:text="This should be visible"
/>
</FrameLayout>
ListFragment.kt
class ListFragment : Fragment(R.layout.fragment_list)
Despite this dead-simple setup, I see a blank screen (just an app bar) and debug listeners added to the ListFragment class init don't ever get called. Why isn't my navGraph initializing an instance of the fragment?

Documentation:
NavHostFragment provides an area within your layout for self-contained navigation to occur.
You are missing to declare the fragment placeholder as a NavHostFragment in the FragmentContainerView via the android:name attribute; and therefore the navigation won't occur.
<androidx.fragment.app.FragmentContainerView
....
android:name="androidx.navigation.fragment.NavHostFragment"

NavigationFragment does not show content

I have followed a guide on creating android navigation with the androidx navigation package. However, I am having troubles displaying anything. When the app starts it shows and empty activity and not the content of my fragment.
Do you have to do anything extra in order to let it show the start screen of the navigation graph?
Launcher xml
<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_height="match_parent"
android:layout_width="match_parent">
<fragment
android:id="#+id/launcherNavHostFragment"
android:name="androidx.navigation.fragment.NavHostFragment"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:navGraph="#navigation/navigation_launcher" />
</FrameLayout>
Navigation graph (navigation_launcher)
<?xml version="1.0" encoding="utf-8"?>
<navigation xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="#+id/navigation_launcher"
app:startDestination="#id/launcherFragment">
<fragment
android:id="#+id/launcherFragment"
android:name="com.myapp.Views.LauncherFragment"
android:label="fragment_launcher"
tools:layout="#layout/fragment_launcher" >
<action
android:id="#+id/action_launcherFragment_to_mainActivity"
app:destination="#id/mainActivity" />
</fragment>
<activity
android:id="#+id/mainActivity"
android:name="com.myapp.Views.MainActivity"
android:label="activity_main"
tools:layout="#layout/activity_main" />
</navigation>
The fragments are just basic fragments with a text view inside. Nothing special here.
Any ideas on what is missing?

As far as I see from the code you posted there are some errors in your configuration:
The nav host fragment should be contained in activity_main.xml (or your main activity layout file, the main activity should be defined in your manifest file and it's the one responsible to load the first fragment displayed by the app
The launcher fragment layout should not contain a NavHostFragment itself, but it should have some views inside the frame layout (a textview displaying some text for example)
- activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="#+id/container"
android:layout_width="match_parent"
android:layout_height="match_parent">
<fragment
android:id="#+id/nav_host_fragment"
android:name="androidx.navigation.fragment.NavHostFragment"
android:layout_width="match_parent"
android:layout_height="0dp"
app:defaultNavHost="true"
app:layout_constraintBottom_toTopOf="#+id/nav_view"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:navGraph="#navigation/navigation_launcher" />
</androidx.constraintlayout.widget.ConstraintLayout>
- fragment_launcher.xml
<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_height="match_parent"
android:layout_width="match_parent">
<TextView android:text="I'm the launcher fragment"
android:layout_height="wrap_content"
android:layout_width="wrap_content" />
</FrameLayout>

Screen white when navigate to destination fragment using navigation architecture component Android

I'm using a navigation graph to navigate from fragment A to B with animation slide up duration =0.4s, but while 0.4s before fragment B appears, fragment A becomes a white screen, not keep state data and UI before.
Update:
I tried to clone a sample project with some background color config at all screen. And I found that when navigating to fragment B, fragment A is removed and replaced by fragment B, so the main activity layout contains fragment is visible with the background color of it during 0.4s.
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#F1E78C"
tools:context="com.myricseptember.countryfact.ui.MainActivity">
<fragment
android:id="#+id/navigationHostFragment"
android:name="androidx.navigation.fragment.NavHostFragment"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:defaultNavHost="true"
app:navGraph="#navigation/countryfact_navigation_graph"/>
</android.support.constraint.ConstraintLayout>
fragment_country_list.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#123456">
<android.support.v7.widget.RecyclerView
android:id="#+id/countryRecyclerView"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_alignParentStart="true"
android:layout_alignParentTop="true"
app:layoutManager="android.support.v7.widget.LinearLayoutManager"
tools:listitem="#layout/layout_list_item" />
</RelativeLayout>
fragment_country_detail.xml
<?xml version="1.0" encoding="utf-8"?>
<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#CAEACB">
<android.support.constraint.ConstraintLayout
android:layout_width="match_parent"
android:layout_height="match_parent">
</android.support.constraint.ConstraintLayout>
</ScrollView>
countryfact_navigation_graph.xml
<?xml version="1.0" encoding="utf-8"?>
<navigation xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="#+id/countryfact_navigation_graph"
app:startDestination="#id/countryListFragment">
<fragment
android:id="#+id/countryListFragment"
android:name="com.myricseptember.countryfact.ui.list.CountryListFragment"
android:label="Country Fact"
tools:layout="#layout/fragment_country_list">
<action
android:id="#+id/action_countryListFragment_to_countryDetailsFragment"
app:destination="#id/countryDetailsFragment"
app:enterAnim="#anim/slide_up"
app:popExitAnim="#anim/slide_down" />
</fragment>
<fragment
android:id="#+id/countryDetailsFragment"
android:name="com.myricseptember.countryfact.ui.details.CountryDetailsFragment"
android:label="CountryDetailsFragment"
tools:layout="#layout/fragment_country_details" />
/>
</navigation>
And video record of issues:
=> How to custom navigation add fragment (not remove-replace) or custom handle remove A after fragment B transaction up?

Android jetpack navigation producing an unexpected error

I am trying to use the new navigation graph in android for swapping between fragments. However, I get an error saying :
This navigation graph is not referenced from any layout files (expected to find it in at least one layout file with a NavHostFragment with app:navGraph="#navigation/nav_graph" attribute). Navigation resource files must be referenced from a NavHostFragment in a layout in order to be relevant.
I have seen many poeple with the same error, but everyone seemed to have done something wrong and could correct it. In my case, I am almost 100% sure my code is ok...
Here is my nav_graph.xml :
<navigation xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="#+id/nav_graph"
app:startDestination="#id/mainFragment">
<fragment
android:id="#+id/mainFragment"
android:name="com.ouimet.budget.MainFragment"
android:label="fragment_main"
tools:layout="#layout/fragment_main" >
<action
android:id="#+id/action_mainFragment_to_expenseFragment"
app:destination="#id/expenseFragment" />
</fragment>
<fragment
android:id="#+id/expenseFragment"
android:name="com.ouimet.budget.ExpenseFragment"
android:label="fragment_expense"
tools:layout="#layout/fragment_expense" />
</navigation>
Along with my MainActivity's resource file activity_main.xml (which references the nav_graph.xml):
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">
<androidx.fragment.app.FragmentContainerView
android:id="#+id/nav_host_fragment"
android:name="androidx.navigation.fragment.NavHostFragment"
android:layout_width="0dp"
android:layout_height="0dp"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintBottom_toBottomOf="parent"
app:defaultNavHost="true"
app:navGraph="#navigation/nav_graph" />
</androidx.constraintlayout.widget.ConstraintLayout>
And my fragment_main.xml:
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainFragment"
android:id="#+id/parentLayout">
<Button
android:id="#+id/view_expense_btn"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Entrer une dépense"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintLeft_toRightOf="parent"
app:layout_constraintRight_toLeftOf="parent"
app:layout_constraintTop_toTopOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>
As we can see, my nav_graph is referenced.. Also, when I compile and run the code, the transition between the fragments works! Is this a known issue or just me not seeing something?
Thank you for your help!
Alexandre

Right way to inflate android.support.v4.app.fragment from xml

Please, help.
Which is right?
Like this:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="horizontal" >
<android.support.v4.app.fragment
android:id="#+id/advertListFragment"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:name="com.myapp.fragment.AdvertListFragment"/>
Or like this:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="horizontal" >
<fragment
android:id="#+id/advertListFragment"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:name="com.myapp.fragment.AdvertListFragment"/>
Without prefix "android.support.v4".
P.s. I haven't more details

Use
<fragment
...
inflated in an activity that extends android.support.v4.app.FragmentActivity.
For further details, it's FragmentActivity.onCreateView() that handles the inflation for fragment elements.