android - How to set RecyclerView app:layoutManager="" from XML?

As you can check in the doc:

Class name of the Layout Manager to be used.

The class must extend android.support.v7.widget.RecyclerView$LayoutManager and have either a default constructor or constructor with the signature (android.content.Context, android.util.AttributeSet, int, int).

If the name starts with a '.', application package is prefixed. Else, if the name contains a '.', the classname is assumed to be a full class name. Else, the recycler view package name (android.support.v7.widget) is prefixed.

<android.support.v7.widget.RecyclerView
    xmlns:app="http://schemas.android.com/apk/res-auto"
    app:layoutManager="android.support.v7.widget.GridLayoutManager" >

With androidx you can use:

<androidx.recyclerview.widget.RecyclerView
     xmlns:app="http://schemas.android.com/apk/res-auto"
     app:layoutManager="androidx.recyclerview.widget.GridLayoutManager">

if you want use it with LinearLayoutManager

<android.support.v7.widget.RecyclerView
    xmlns:app="http://schemas.android.com/apk/res-auto"
    app:layoutManager="android.support.v7.widget.LinearLayoutManager" >

that equivalent to

LinearLayoutManager mLayoutManager = new LinearLayoutManager(getApplicationContext());
mRecyclerView.setLayoutManager(mLayoutManager);

And I came here looking for androidx version though it was pretty easy to figure out, here it is

LinearLayoutManager:

app:layoutManager="androidx.recyclerview.widget.LinearLayoutManager"

Example:

<androidx.recyclerview.widget.RecyclerView
    android:id="@+id/recyclerView"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    app:layoutManager="androidx.recyclerview.widget.LinearLayoutManager"/>

GridLayoutManager:

app:layoutManager="androidx.recyclerview.widget.GridLayoutManager"

Example:

<androidx.recyclerview.widget.RecyclerView
    android:id="@+id/recyclerView"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    app:spanCount="2"
    app:layoutManager="androidx.recyclerview.widget.GridLayoutManager"/>

As you can see in examples above you can control the orientation from within xml using

android:orientation="vertical"

and

android:orientation="horizontal"

And to set the number of columns for GridLayoutManager using

app:spanCount="2"

The most common ones that I use are:

<androidx.recyclerview.widget.RecyclerView
    app:layoutManager="androidx.recyclerview.widget.GridLayoutManager" 
    tools:listitem="@layout/grid_item"
    android:orientation="vertical" app:spanCount="3"/>

And:

<androidx.recyclerview.widget.RecyclerView
    app:layoutManager="androidx.recyclerview.widget.LinearLayoutManager"
    tools:listitem="@layout/grid_item"
    android:orientation="vertical"/>

It's recommended to set listitem , so that you'd see how it could look in the preview of the layout editor.

If you want to have the order reversed though, I think you have to do it in code instead, and use "tools" in XML if you really want to see something...