Previewing horizontal recyclerview in android studio

Add a LayoutManager and set a horizontal orientation.

Here an example:

<android.support.v7.widget.RecyclerView
    android:id="@+id/homesRecyclerView"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="horizontal"
    app:layoutManager="android.support.v7.widget.LinearLayoutManager"
    android:layout_centerVertical="true"
    />

If you are using androidx libraries:

<androidx.recyclerview.widget.RecyclerView
    android:id="@+id/homesRecyclerView"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="horizontal"
    app:layoutManager="androidx.recyclerview.widget.LinearLayoutManager"
    android:layout_centerVertical="true"
    />

Just use in your layout the app:layoutManager and the android:orientation attributes and add them also using the tools namespace.
Something like:

<androidx.recyclerview.widget.RecyclerView
    android:id="@+id/recyclerView"
    android:orientation="horizontal"
    app:layoutManager="androidx.recyclerview.widget.LinearLayoutManager"
    tools:listitem="@layout/ly_item"
    tools:layoutManager="androidx.recyclerview.widget.LinearLayoutManager"
    tools:orientation="horizontal"
    ../>

the accepted answer works accurately. For androidx just use this in your recyclerView

app:layoutManager="androidx.recyclerview.widget.LinearLayoutManager" android:orientation="horizontal"