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RecyclerView in scrollview cut last items

I have fragment with 2 RecyclerView.
I get some data from api and add it for RecyclerViews in ArrayLists, then notify view that data was changed. For some reason, the last element(s) of the RecyclerViews is getting cut-off. When i get 8 object - RVs show only 5 of them. On small screens even less. I am disable RVs scrolling, and want use one ScrollView for all fragment content.
This is the XML of the fragment:s
<?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=".screens.view.MainFragment">
<androidx.swiperefreshlayout.widget.SwipeRefreshLayout
android:id="#+id/onDutyMainRefreshLayout"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent">
<ScrollView
android:layout_width="match_parent"
android:layout_height="wrap_content"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent">
<androidx.constraintlayout.widget.ConstraintLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:paddingHorizontal="#dimen/margin_m"
android:paddingVertical="#dimen/margin_m">
<TextView
android:id="#+id/requestTitle"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
android:fontFamily="#font/sfprotext_semibold"
android:textStyle="bold"
android:textSize="#dimen/on_duty_main_subtitle_font_size"
android:textColor="#color/dark_liver"
android:text="Requests"
tools:text="Requests"/>
<Button
android:id="#+id/showAllRequestsButton"
style="#style/ShowAllButtonDark"
app:layout_constraintBottom_toBottomOf="#+id/requestTitle"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintTop_toTopOf="#+id/requestTitle"
tools:ignore="TouchTargetSizeCheck"
android:text="Show All"
tools:text="Show All" />
<androidx.recyclerview.widget.RecyclerView
android:id="#+id/requestsRecyclerView"
android:layout_width="match_parent"
android:layout_marginTop="#dimen/on_duty_recycler_view_margin_top"
android:layout_height="wrap_content"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="#+id/requestTitle" />
<TextView
android:id="#+id/groupTitle"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:fontFamily="#font/sfprotext_semibold"
android:textColor="#color/dark_liver"
android:textSize="#dimen/on_duty_main_subtitle_font_size"
android:textStyle="bold"
android:layout_marginTop="#dimen/margin_m"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="#+id/requestsRecyclerView"
android:text="Groups"
tools:text="Groups" />
<androidx.recyclerview.widget.RecyclerView
android:id="#+id/groupsRecyclerView"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginTop="#dimen/on_duty_recycler_view_margin_top"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="#+id/groupTitle" />
</androidx.constraintlayout.widget.ConstraintLayout>
</ScrollView>
</androidx.swiperefreshlayout.widget.SwipeRefreshLayout>
</androidx.constraintlayout.widget.ConstraintLayout>
I try found solution in other question like that, but nothing helped me.
For examle, i tryed some solution from RecyclerView is cutting off the last item

Unfixed element on top of RecyclerView

I have something like 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:layout_width="match_parent"
android:layout_height="match_parent"
android:padding="10dp"
tools:context=".ui.base.core.example">
<TextView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:text="hello" />
<androidx.recyclerview.widget.RecyclerView
android:id="#+id/topicsRecyclerView"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:layoutManager="androidx.recyclerview.widget.LinearLayoutManager"
app:layout_behavior="#string/appbar_scrolling_view_behavior"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent"
tools:listitem="#layout/item_topics" />
</androidx.constraintlayout.widget.ConstraintLayout>
When I run this, the TextView element is fixed and scrolls when I scroll through my RecyclerView. Is there a way so that I can make it where the TextView element is on top of the RecyclerView and when I scroll it's not fixed? I'm using a TextView to just do testing, but eventually I'd like to have a header on top of the RecyclerView that shouldn't be scrollable with the RecyclerView and just stay on top.

You need to set up constraints.
Approximately like this:
<TextView
android:id="#+id/textView"
android:layout_width="0dp"
android:layout_height="wrap_content"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintBottom_toTopOf="#id/topicsRecyclerView" />
<androidx.recyclerview.widget.RecyclerView
android:id="#+id/topicsRecyclerView"
android:layout_width="0dp"
android:layout_height="0dp"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintTop_toBottomOf="#id/textView"
app:layout_constraintBottom_toBottomOf="parent" />

Constraintlayout Vertical Bias not working in two views Android

I am using constraint layout with a vertical bias to fill view in recycler view. I successfully did that.
<?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"
android:background="#color/white">
<androidx.recyclerview.widget.RecyclerView
android:id="#+id/recylerview"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:paddingStart="10dp"
android:paddingEnd="10dp"
android:paddingBottom="10dp"
app:layoutManager="androidx.recyclerview.widget.LinearLayoutManager"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0" />
</androidx.constraintlayout.widget.ConstraintLayout>
My recyclerview items showing me in reverse order because I want to make chat application. So I added reverseLayout and stackFromEnd true. So it look like this.
If my item is single my ui convert into like this by above xml code
Now I want to add edittext and button in bottom. Its not working vertical bias. Does any one know how to fix. Any suggestion to what can i use
Expected Output
Scenerio 1
Scenerio 2
Actual Output
I tried this code
<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"
android:background="#color/white">
<androidx.recyclerview.widget.RecyclerView
android:id="#+id/recyclerView"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:paddingStart=10dp"
android:paddingEnd="10dp"
android:paddingBottom="10dp"
app:layoutManager="androidx.recyclerview.widget.LinearLayoutManager"
app:layout_constraintBottom_toTopOf="#+id/inputContainer"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.0" />
<androidx.constraintlayout.widget.ConstraintLayout
android:id="#+id/inputContainer"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:paddingBottom="20dp"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="#+id/crecyclerView">
<EditText
android:id="#+id/editTextContainer"
android:layout_width="200dp"
android:layout_height="match_parent"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toStartOf="#+id/button"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<Button
android:id="#+id/button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="button"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toEndOf="#+id/editTextContainer"
app:layout_constraintTop_toTopOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>
</androidx.constraintlayout.widget.ConstraintLayout>
UPDATE
After adding #MartinMarconcini answer it fixed my Scenario 2. I want to fix as Scenario 1 as well.

The idea is that your RV will handle its own item size and space by itself. You don't need to worry about this.
The Remainder of the space, will be used by ConstraintLayout.
So you need to pin the RV and the "Bottom Container" together. This would by default cause the CL to try to pull and balance layouts, so you have to tell the bottom container to be biased at the bottom.
In pseudo-XML:
<ConstraintLayout>
<RecyclerView
width=0dp
height=0dp
start/end = parent
TopToTop=parent
BottomToTopOf=BottomContainer
>
<BottomContainer>
width=0dp
height=wrap_content
TopToBottomOf=RecyclerView
BottomToBottomOf=parent
start/end = parent>
</ConstraintLayout>
Now this needs one more thing, because the RV would take all the space, you want to ensure the BottomContainer has more information about where it wants to be placed.
So you add:
app:layout_constraintVertical_bias="1.0"
to the Bottom Container.
This means, vertically, as "bottom" as you can. (0.0 would be the opposite).
The end result is:
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools">
<androidx.recyclerview.widget.RecyclerView
android:id="#+id/recylerview"
android:layout_width="0dp"
android:layout_height="0dp"
android:paddingStart="10dp"
android:paddingEnd="10dp"
android:paddingBottom="10dp"
app:layoutManager="androidx.recyclerview.widget.LinearLayoutManager"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
tools:listitem="#android:layout/simple_list_item_2" />
<androidx.constraintlayout.widget.ConstraintLayout
android:layout_width="0dp"
app:layout_constraintVertical_bias="1.0"
android:layout_height="wrap_content"
android:id="#+id/bottomContainer"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintTop_toBottomOf="#id/recylerview"
app:layout_constraintBottom_toBottomOf="parent">
<EditText
android:id="#+id/editTextContainer"
android:layout_width="0dp"
android:layout_height="wrap_content"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toStartOf="#+id/button"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<Button
android:id="#+id/button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="button"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toEndOf="#+id/editTextContainer"
app:layout_constraintTop_toTopOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>
</androidx.constraintlayout.widget.ConstraintLayout>
Which looks like this:
UPDATE
If you add both
app:stackFromEnd="true"
app:reverseLayout="true"
It works the same way, except the item "0" is at the bottom, and the "last" item is at the top. Adding another item would add it at the top but the BottomContainer has no participation (or influence) over this:

Android: Show button just below to the recylerview but always on the screen

On the screen, I want to show RecyclerView which start from the top and at the end of the RecyclerView, there is a button.
When RecyclerView is not occupying the entire screen then the Button will sit just below the RecyclerView.
When RecylerView is scrollable then in this case button will sit on the bottom of the screen.
I tried this code. But the problem here, RecyclerView sits in the centre. In my case, it will always start from the top(after the action bar).
Following code I tried:
main layout:
<?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"
android:background="#b6d7a8" >
<LinearLayout
android:id="#+id/actionBarTermsAndCondition"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:background="#color/dark_gray"
android:gravity="center_vertical"
android:minHeight="70dp"
android:orientation="horizontal"
android:paddingStart="16dp"
android:paddingTop="10dp"
android:paddingEnd="16dp"
android:paddingBottom="10dp"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" >
<ImageView
android:id="#+id/closeButton"
android:layout_width="#dimen/spacing_2x"
android:layout_height="#dimen/spacing_2x"
android:layout_gravity="center_vertical"
android:layout_marginEnd="#dimen/spacing_2_5x"
android:clickable="true"
android:contentDescription="#string/close"
android:foreground="?selectableItemBackground"
android:src="#drawable/cross"
android:visibility="invisible" />
<TextView
android:id="#+id/route"
style="#style/ScreenTitle"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center_vertical"
android:contentDescription="Import Venue"
android:fontFamily="#font/roboto"
android:text="Import Venue"
android:textColor="#color/white"
tools:text="Something" />
</LinearLayout>
<androidx.recyclerview.widget.RecyclerView
android:id="#+id/list"
android:name="DataManagementFragment"
android:layout_width="match_parent"
android:layout_height="wrap_content"
app:layoutManager="LinearLayoutManager"
app:layout_constrainedHeight="true"
app:layout_constraintBottom_toTopOf="#id/constraint_layout_cloud_access"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="#+id/actionBarTermsAndCondition"
app:layout_constraintVertical_chainStyle="packed"
tools:itemCount="3"
tools:listitem="#layout/fragment_data_management_list_row" />
<androidx.constraintlayout.widget.ConstraintLayout
android:id="#+id/constraint_layout_cloud_access"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:background="#FEAB8C"
android:paddingStart="16dp"
android:paddingTop="10dp"
android:paddingBottom="21dp"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="#id/list">
<TextView
android:id="#+id/text_cloud_access"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:fontFamily="#font/roboto"
android:text="Cloud access"
android:textColor="#3C3C41"
android:textSize="16dp"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
tools:text="Cloud access" />
<TextView
android:id="#+id/text_import_venue"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:fontFamily="#font/roboto"
android:text="Import venue"
android:textColor="#3C3C41"
android:textSize="16dp"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="#id/text_cloud_access"
tools:text="Import place" />
</androidx.constraintlayout.widget.ConstraintLayout>
</androidx.constraintlayout.widget.ConstraintLayout>
RecyclerView row layout:
<?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:background="#fff2cc"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:paddingEnd="#dimen/spacing_3x"
android:paddingStart="#dimen/spacing_2x"
android:paddingBottom="#dimen/spacing_2_5x"
android:paddingTop="#dimen/spacing_2_5x"
android:orientation="horizontal"
tools:showIn="#layout/fragment_data_management">
<TextView
android:id="#+id/text_floor_name"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:fontFamily="#font/roboto"
android:textAppearance="?attr/textAppearanceListItem"
android:textColor="#3C3C41"
android:textSize="16dp"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
tools:text="Preloaded" />
<TextView
android:id="#+id/text_venue_name"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:fontFamily="#font/roboto"
android:textAppearance="?attr/textAppearanceListItem"
android:textColor="#636367"
android:textSize="12dp"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="#id/text_floor_name"
tools:text="ABC" />
<ImageView
android:id="#+id/imageView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
app:srcCompat="?android:attr/listChoiceIndicatorMultiple"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<ImageView
android:id="#+id/imageView2"
android:layout_width="match_parent"
android:layout_height="wrap_content"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:srcCompat="?attr/dividerHorizontal" />
</androidx.constraintlayout.widget.ConstraintLayout>

Your RecyclerView is centering between two other layouts. Add
app:layout_constraintVertical_bias="0.0"
to the XML for the RecyclerView to move it to the top. You can look up how bias works in the ConstraintLayout documentation.

I think you can achieve what you want with a guideline. The steps would be the following:
Create an horizontal guideline that sits at the 90% of the screen, meaning that it will be really close to the bottom, on the 10% left is where your button will be when the recycler view becomes scrollable.
Set the bottom constraint of the recycler view to match the top of the guideline and the top of the recycler view to the top of the screen. This will cause that the recycler view appears on the half of your screen.
Set the vertical bias of your recycler view to 0.0, this will stick the recycler view to the top.
Set the top constraint of the button to match the bottom of the recycler view, this will cause that it will stick to the bottom of the recycler view, but since the recycler view (thanks to the guideline) will only grow to 90% of the screen, the button will sit at the bottom of the screen as you want.
It's important to add the following attribute to the recycler view:
app:layout_constrainedHeight="true"
The layout related to the button and recycler view should look something like:
<?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.recyclerview.widget.RecyclerView
android:id="#+id/list"
android:layout_width="match_parent"
android:layout_height="wrap_content"
app:layout_constrainedHeight="true"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintBottom_toTopOf="#+id/guideline"
app:layout_constraintVertical_bias="0.0"
tools:itemCount="130"/>
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Button text"
app:layout_constraintTop_toBottomOf="#+id/list"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"/>
<androidx.constraintlayout.widget.Guideline
android:id="#+id/guideline"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="horizontal"
app:layout_constraintGuide_percent="0.9"/>
</androidx.constraintlayout.widget.ConstraintLayout>
With few items:
With many items:

Placing horizontal recyclerview at a specific position using ConstraintLayout

I want to place my horizonatl recyclerview at 30% screen width from start
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent">
<android.support.v7.widget.RecyclerView
android:id="#+id/recycler"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:clipToPadding="false"
android:orientation="horizontal"
android:paddingStart="20dp"
android:paddingEnd="20dp"
android:background="#android:color/white"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toEndOf="#id/guideline" />
<android.support.constraint.Guideline
android:id="#+id/guideline"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:orientation="vertical"
app:layout_constraintGuide_percent="0.3" />
</android.support.constraint.ConstraintLayout>
But it is not recyclerview not appearing on screen working any idea how to achieve this.

You never gave your recyclerView a vertical constraint so what happened is that at the run time your recyclerView just jumped to the top of the screen.
When I copied your code I saw this error:
This view is not constrained vertically: at runtime, it will jump to the top unless you add a vertical constraint
Some tip - if you see the red line on your view in the XML/the red warning button from the design you should really look at the error and change your layout accordingly.
And of course, I won't leave you without a good working layout - here is the layout that I made for the recyclerView to start at 30% of the screen, I have checked it and its working. (i was working with androidx but just change it to the support library if you want)
<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">
<androidx.constraintlayout.widget.Guideline
android:id="#+id/guideline2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:orientation="vertical"
app:layout_constraintGuide_percent="0.3"/>
<androidx.recyclerview.widget.RecyclerView
android:layout_width="0dp"
android:layout_height="0dp"
android:layout_marginStart="8dp"
android:layout_marginTop="8dp"
android:layout_marginEnd="8dp"
android:layout_marginBottom="16dp"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.506"
app:layout_constraintStart_toStartOf="#+id/guideline2"
app:layout_constraintTop_toTopOf="parent"
android:background="#color/colorPrimaryDark"/>

your RecyclerView is missing the vertical constraints; Add at least one so that the view can be rendered.
constrained to top:
app:layout_constraintTop_toTopOf="parent"
if you want it to use the whole parent, add these too:
android:layout_height="0dp"
app:layout_constraintBottom_toBottomOf="parent"

Remove the ConstraintLayout and use Linearlayout instead, than use the android:weight= property accordingly in both guideline and RecyclerView.

This will work fine for you
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent">
<android.support.v7.widget.RecyclerView
android:id="#+id/recycler"
android:layout_width="0dp"
android:layout_height="0dp"
android:clipToPadding="false"
android:orientation="horizontal"
android:paddingStart="20dp"
android:paddingEnd="20dp"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintEnd_toEndOf="#id/guideline"
app:layout_constraintBottom_toBottomOf="parent"
/>
<androidx.constraintlayout.widget.Guideline
android:id="#+id/guideline"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:orientation="vertical"
app:layout_constraintGuide_percent=".3" />
</android.support.constraint.ConstraintLayout>