Develop Reference

How to Set Recycler View Height Dynamically Using wrap_content?

I have a fragment containing a recycler view which is populated using data fetched from a server. This fragment is inside a FragmentContainerView within the activity. I want the height of the recyclerView to be dynamic. Essentially using wrap_content as the height parameter, but when I do that the recyclerView has a height of 0 and doesn't show up at all.
Why doesn't wrap_content dynamically adjust the height for my fragmentContainerView height?
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">
<androidx.recyclerview.widget.RecyclerView
android:id="#+id/calendarRecyclerView"
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" />
</androidx.constraintlayout.widget.ConstraintLayout>
Activity
<?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=".activities.DashboardActivity">
<androidx.fragment.app.FragmentContainerView
android:id="#+id/fragmentContainerView"
android:name="com.yambo.yates.fragments.WorkoutCalendarFragment"
android:layout_width="0dp"
android:layout_height="wrap_content"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
tools:layout="#layout/workout_calendar_fragment" />
</androidx.constraintlayout.widget.ConstraintLayout>

RecyclerViews already dynamically adjust height based on contents. So as long as your XML is at least wrap_content it should display everything. Are you sure your data is valid?
Also, if your fragment only contains the RecyclerView you can remove the parent ConstraintLayout and change your XML to:
<androidx.recyclerview.widget.RecyclerView
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="#+id/calendarRecyclerView"
android:layout_width="match_parent"
android:layout_height="match_parent" />

Make RecycleView show items in the middle of the screen, if the items are few

I have programmed a simple linear RecycleView for my new alarm application. Since I am very new to Android programming I have run into such a question: now, all the items I have are shown from top to bottom, even if there are only, say 3 items at all. It doesn't look too good and not convenient also. Is there some way, if there are only few items in the list, to show them in the middle, rather than from top to bottom?
Thank you!!
My current main XML code is:
<?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="#drawable/background"
tools:context=".MainActivity">
<androidx.recyclerview.widget.RecyclerView
android:id="#+id/recycler_view"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fadeScrollbars="true"
android:scrollbars="vertical"
android:layout_marginTop="27dp"
android:layout_marginBottom="36dp"
android:requiresFadingEdge="vertical|horizontal"
tools:listitem="#layout/alarms_view" />
</androidx.constraintlayout.widget.ConstraintLayout>

You should change the recycleView android:layout_height="match_parent" to
android:layout_height="wrap_content"
then add these lines in your RecycleView.
app:layout_constraintCircleRadius="0dp"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.5"
app:layout_constraintStart_toStartOf="parent"

You can center all the recyclerView in the middle
for that change your recyclerView like the xml below
<androidx.recyclerview.widget.RecyclerView
android:id="#+id/recycler_view"
android:layout_width="0dp"
android:layout_height="wrap_content"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
android:fadeScrollbars="true"
android:scrollbars="vertical"
android:layout_marginTop="27dp"
android:layout_marginBottom="36dp"
android:requiresFadingEdge="vertical|horizontal"
tools:listitem="#layout/alarms_view" />
and when you add new item your recyclerview expand up to the height of screen

Add layout gravity to parent layout and change recyclerview height to wrap content like this:
<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:layout_gravity="center"
android:background="#drawable/background"
tools:context=".MainActivity">
<androidx.recyclerview.widget.RecyclerView
android:id="#+id/recycler_view"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:fadeScrollbars="true"
android:scrollbars="vertical"
android:layout_marginTop="27dp"
android:layout_marginBottom="36dp"
android:requiresFadingEdge="vertical|horizontal"
tools:listitem="#layout/alarms_view" />

(android) How to place a view below other views in constraint layout

This picture is state of layout
I want to place the RecyclerView below the Button
However, as you can see, even with layout_constraintTop_toBottomOf, the RecyclerView is not placed
under the Button
There is a condition, the size of the RecyclerView must be math_parent.
This is because you are using a nested recycler view and you are dynamically adding items, otherwise
the last nested recycler view's item will be cut off and not visible when adding dynamically..
If I set the height of a view to match_parent in the constraint layout, is there any way to place it
below other views?
This is XML file.
activity_write_routine.xml
<?xml version="1.0" encoding="utf-8"?>
<androidx.coordinatorlayout.widget.CoordinatorLayout
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"
xmlns:app="http://schemas.android.com/apk/res-auto"
tools:context=".data.DailyRecordDetailActivity">
<com.google.android.material.appbar.AppBarLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:theme="#style/Theme.AppBarOverlay"
app:elevation="0dp">
<androidx.appcompat.widget.Toolbar
android:layout_width="match_parent"
android:layout_height="wrap_content">
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="match_parent">
<TextView
android:id="#+id/body_part_detail_title"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="P A R T"
android:textColor="#color/white"
android:textAppearance="#style/TextAppearance.AppCompat.Widget.ActionBar.Title"
android:layout_centerHorizontal="true"/>
</RelativeLayout>
</androidx.appcompat.widget.Toolbar>
</com.google.android.material.appbar.AppBarLayout>
<androidx.constraintlayout.widget.ConstraintLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_margin="10dp"
app:layout_behavior="com.google.android.material.appbar.AppBarLayout$ScrollingViewBehavior">
<Button
android:id="#+id/add_routine"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="A D D"
android:backgroundTint="#color/light_green"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintRight_toRightOf="parent"/>
<androidx.recyclerview.widget.RecyclerView
android:id="#+id/routine_recyclerview"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:scrollbars="vertical"
app:layout_constraintTop_toBottomOf="#+id/add_routine"/>
</androidx.constraintlayout.widget.ConstraintLayout>
</androidx.coordinatorlayout.widget.CoordinatorLayout>

change the height to 0dp, and constraint the bottom of recyclerview to parent
<androidx.recyclerview.widget.RecyclerView
android:id="#+id/routine_recyclerview"
android:layout_width="match_parent"
android:layout_height="0dp"
android:scrollbars="vertical"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintTop_toBottomOf="#+id/add_routine"/>

How to centre a parent ViewGroup?

I have a parent ConstraintLayout in my fragment.xml:
<?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="400dp"
android:maxHeight="400dp"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintBottom_toBottomOf="parent"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:background="#color/colorPopupBackground"
android:fadeScrollbars="false"
android:id="#+id/profile_layout"
android:elevation="1dp">
as you can see i've set a maxHeight and constrained it on every side - so you would think it should centre vertically on the screen. However the ConstraintLayout sits on the top vertically.
Any idea?

Just remove bottom constraint because when you set both side constraint and set custom width then it will be center of both constraint, SO update your code like bellow
<?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="400dp"
android:maxHeight="400dp"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintEnd_toEndOf="parent"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:background="#color/colorPopupBackground"
android:fadeScrollbars="false"
android:id="#+id/profile_layout"
android:elevation="1dp">

How to set Android ListView's cell height as half of cell width?

I am trying to use constraint layout as below. But the aspect ratio is not respected in the actual layout. Instead, the height is actually wrapping the content inside
<android.support.constraint.ConstraintLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:id="#+id/content"
android:layout_height="0dp"
android:layout_width="match_parent">
<!-- some content inside -->
</android.support.constraint.ConstraintLayout>
I then think it might be because I didn't set width="0dp" (let constraint decide the width). So I tried another way like below. But then the width becomes zero.
What is the correct way of doing it?
<android.support.constraint.ConstraintLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:id="#+id/content"
android:layout_height="0dp"
android:layout_width="0dp"
app:layout_constraintStart_toEndOf="parent"
app:layout_constraintEnd_toEndOf="parent">
<!-- some content inside -->
</android.support.constraint.ConstraintLayout>
EDIT: working solution after inspired by Anddenver 's answer (with modification):
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="wrap_content"
xmlns:app="http://schemas.android.com/apk/res-auto">
<FrameLayout
android:background="#android:color/holo_green_dark"
android:layout_width="0dp"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintEnd_toEndOf="parent"
android:layout_height="0dp"
app:layout_constraintDimensionRatio="2:1">
</FrameLayout>
</android.support.constraint.ConstraintLayout>
Further Edit:
It seems I need to wrap one more layer of constraint layout for my inner contents .... :
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="wrap_content"
xmlns:app="http://schemas.android.com/apk/res-auto">
<FrameLayout
android:background="#android:color/holo_green_dark"
android:layout_width="0dp"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintEnd_toEndOf="parent"
android:layout_height="0dp"
app:layout_constraintDimensionRatio="2:1">
<android.support.constraint.ConstraintLayout
android:layout_width="match_parent"
android:layout_height="match_parent">
<actual contents here..../>
</android.support.constraint.ConstraintLayout>
</FrameLayout>
</android.support.constraint.ConstraintLayout>
Or, just remove the FrameLayout, and wrap ConstraintLayout inside a ConstraintLayout:
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="wrap_content"
xmlns:app="http://schemas.android.com/apk/res-auto">
<android.support.constraint.ConstraintLayout
android:background="#android:color/holo_green_dark"
android:layout_width="0dp"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintEnd_toEndOf="parent"
android:layout_height="0dp"
app:layout_constraintDimensionRatio="2:1">
contents here...
</android.support.constraint.ConstraintLayout>
</android.support.constraint.ConstraintLayout>

You need inner view for that, for example:
<android.support.constraint.ConstraintLayout
android:layout_width="match_parent"
android:layout_height="wrap_content">
<FrameLayout
android:background="#color/colorPrimary"
android:layout_width="match_parent"
android:layout_height="0dp"
app:layout_constraintDimensionRatio="1:1">
<YOUR CONTENT>
</FrameLayout>

For a ListView, you'd need to inflate a custom list_item.xml
and this should be H,2:1, to constrain the height to a 2:1 aspect ratio.
The default android.R.layout.simple_list_item_1 is just a TextView:
<?xml version="1.0" encoding="utf-8"?>
<TextView
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="#android:id/text1"
android:layout_height="0dp"
android:layout_width="0dp"
app:layout_constraintDimensionRatio="H,2:1"
...
/>
see DimensionConstraints.