Develop Reference

How can a fragment be in the whole activity_main layout?

I have a fragment view in my activity main layout, but i can´t put it on the whole layout, I have also bottom mobile navigation, but the problem is at the top of the layout.
With an image is better:
activity_main.xml
The code of that layout is this:
<?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"
android:paddingTop="?attr/actionBarSize">
<com.google.android.material.bottomnavigation.BottomNavigationView
android:id="#+id/nav_view"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_marginStart="0dp"
android:layout_marginEnd="0dp"
android:background="?android:attr/windowBackground"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:menu="#menu/bottom_nav_menu" />
<fragment
android:id="#+id/nav_host_fragment_activity_main"
android:name="androidx.navigation.fragment.NavHostFragment"
android:layout_width="0dp"
android:layout_height="0dp"
app:defaultNavHost="true"
app:layout_constraintBottom_toBottomOf="#+id/nav_view"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:navGraph="#navigation/mobile_navigation" />
</androidx.constraintlayout.widget.ConstraintLayout>
How can I fix that? In the fragment I have a recyclerview

In Your constraintlayout
Remove this Attribute
android:paddingTop="?attr/actionBarSize"
your fragment get full layout size.

Just use LinearLayout with <fragment height=0dp weight=1<fragment

Why doesn't the Fragment size extend to screen size?

I have created a new bottom navigation activity using the android studio wizard. The problem seems to be the activity_main layout. The fragment view isn't extending to the top of the screen, but instead it's covered by the bottom navigation bar.
No matter what I do, I can't move it up.
That's the XML code:
<?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"
android:id="#+id/container"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingTop="?attr/actionBarSize">
<com.google.android.material.bottomnavigation.BottomNavigationView
android:id="#+id/nav_view"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_marginStart="0dp"
android:layout_marginEnd="0dp"
android:background="?android:attr/windowBackground"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:menu="#menu/bottom_nav_menu" />
<fragment
android:id="#+id/nav_host_fragment_activity_main"
android:name="androidx.navigation.fragment.NavHostFragment"
android:layout_width="match_parent"
android:layout_height="match_parent"
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/mobile_navigation" />
</androidx.constraintlayout.widget.ConstraintLayout>

Remove the below padding from the root layout:
android:paddingTop="?attr/actionBarSize"

You need to set
android:layout_width="0dp"
android:layout_height="0dp"
to switch from "normal sizing" to "apply constraint sizing"

Android: Intellij Buttom nav template creates unused space, hides nodes under it

I created an Android project in Intellij with the buttom nav template.
I can not use a certain space on the top (see screenshot) which corelates in size with the buttom nav bar, even though the constrains seem to be right.
As well it hides/converes elements which are placed under it, actually there is a TextView and a spinner.
<?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"
android:paddingTop="?attr/actionBarSize">
<com.google.android.material.bottomnavigation.BottomNavigationView
android:id="#+id/nav_view"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_marginStart="0dp"
android:layout_marginEnd="0dp"
android:background="?android:attr/windowBackground"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:menu="#menu/bottom_nav_menu"/>
<fragment
android:id="#+id/nav_host_fragment_activity_main"
android:name="androidx.navigation.fragment.NavHostFragment"
android:layout_width="match_parent"
android:layout_height="wrap_content"
app:defaultNavHost="true"
app:navGraph="#navigation/mobile_navigation"
android:scrollbars="vertical" app:layout_constraintTop_toTopOf="parent"
app:layout_constraintEnd_toEndOf="parent" app:layout_constraintStart_toStartOf="parent"
app:layout_constraintBottom_toTopOf="#+id/nav_view" android:layout_marginBottom="40dp"
android:paddingBottom="40dp"/>
</androidx.constraintlayout.widget.ConstraintLayout>

You have to remove the fragment height from wrap_content to 0dp i.e match_constraint (match_parent)
match_constraint or 0dp : The view expands as much as possible to meet the constraints on each side (after accounting for the view's margins).
Chain: A chain is a group of views that are linked to each other with bi-directional position constraints. The views within a chain can be distributed either vertically or horizontally. For your case we need a Vertical Chain. See video
And last I remove the android:paddingTop="?attr/actionBarSize" from you ConstraintLayout
Try the below code:
<?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_activity_main"
android:layout_width="match_parent"
android:layout_height="0dp"
android:scrollbars="vertical"
app:defaultNavHost="true"
android:name="androidx.navigation.fragment.NavHostFragment"
app:layout_constraintBottom_toTopOf="#+id/nav_view"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.5"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:navGraph="#navigation/mobile_navigation" />
<com.google.android.material.bottomnavigation.BottomNavigationView
android:id="#+id/nav_view"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:background="?android:attr/windowBackground"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="#+id/nav_host_fragment_activity_main"
app:menu="#menu/bottom_nav_menu"/>
</androidx.constraintlayout.widget.ConstraintLayout>

Remove
android:paddingTop="?attr/actionBarSize"
from your root ConstraintLayout.

GoogleMap fragment inside fragment containing margin/padding at top?

Using the "Activity Bottom Navigation" template in Android Studio, I am then adding a GoogleMap fragment inside one of the default fragments.
The main fragment, unchanged from the template:
<?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"
android:id="#+id/container"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingTop="?attr/actionBarSize">
<com.google.android.material.bottomnavigation.BottomNavigationView
android:id="#+id/nav_view"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_marginStart="0dp"
android:layout_marginEnd="0dp"
android:background="?android:attr/windowBackground"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:menu="#menu/bottom_nav_menu" />
<fragment
android:id="#+id/nav_host_fragment"
android:name="androidx.navigation.fragment.NavHostFragment"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:defaultNavHost="true"
app:layout_constraintBottom_toTopOf="#id/nav_view"
app:layout_constraintHorizontal_bias="0.0"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.0"
app:navGraph="#navigation/mobile_navigation" />
The fragment that contains my mapfragment. Only slightly modified from the template's fragment:
<?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=".ui.map.MapFragment">
<fragment
android:id="#+id/gmap"
android:name="com.google.android.gms.maps.SupportMapFragment"
android:layout_width="match_parent"
android:layout_height="match_parent" />
</androidx.constraintlayout.widget.ConstraintLayout>
I am not including any code in the fragment, because it doesn't matter if there IS code or not - the margin/padding appears at top.
When run, I get the following:
Notice the almost-action-bar madding before the map starts. In the Android Studio designer screen, it IS shows that the fragment is taking up
Am I missing some kind of flag or setting or layout quirk to allow the map area to fill up the entire parent (its own) fragment?

The root ConstraintLayout on your main fragment is causing the empty space:
android:paddingTop="?attr/actionBarSize"
Delete this attribute and the space will disappear.

AndroidStudio random whitespace at top of app

I'm very new to Android Studio and thre's this whitespace that I haven't defined at the top of my app when I launch it, but not in the preview screen in Android Studio:
I have no idea where it's coming from, as the top of my definition XML doesn't define this whitespace:
<?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"
android:id="#+id/scrollContainer"
android:layout_width="match_parent"
android:layout_height="match_parent">
<LinearLayout
android:id="#+id/containerLayout"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:orientation="vertical">
Below this is just two more LinearLayouts inside the one shown above. I've tried just adding text and the whitespace still appears. I also haven't added anything in code for this to appear.
Any help / ideas would be appreciated!
Edit: Below is the 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"
android:id="#+id/container"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingTop="?attr/actionBarSize">
<com.google.android.material.bottomnavigation.BottomNavigationView
android:id="#+id/nav_view"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_marginStart="0dp"
android:layout_marginEnd="0dp"
android:background="?android:attr/windowBackground"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:menu="#menu/bottom_nav_menu" />
<fragment
android:id="#+id/nav_host_fragment"
android:name="androidx.navigation.fragment.NavHostFragment"
android:layout_width="match_parent"
android:layout_height="match_parent"
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/mobile_navigation" />
</androidx.constraintlayout.widget.ConstraintLayout>

In activity_main.xml, try removing the line:
android:paddingTop="?attr/actionBarSize"
This adds padding around the ConstraintLayout content equal to the height of the action bar, which is not needed in this case.