How to make a Linear and a Relative Layout share horizontal screen space as percentages?

How to make a Linear and a Relative Layout share horizontal space as percentages?

The LinearLayout on the left needs to have a percentage width of the screen, and the RelativeLayout on the right can just take up what remains. I had this as two LinearLayout's and it worked fine because I could use the layout_weight attribute, defining width as a percentage, sorta like so:

android:layout_height="match_parent"
android:layout_width="0dp"
android:layout_weight=".20"

But now I need the layout on the right to be a RelativeLayout, and can't figure out how to preserve the desired percentages since RelativeLayout does not have a layout_weight attribute. What I need looks something like:

Note: It's better to use ConstraintLayout now without worring about nested views.

In RelativeLayout documentation:

Note: For better performance and tooling support, you should instead build your layout with ConstraintLayout.

Here's the ConstraintLayout version:

<?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">

    <View
        android:id="@+id/view1"
        android:layout_width="0dp"
        android:layout_height="match_parent"
        android:background="@color/teal_700"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintWidth_percent="0.2" />

    <View
        android:layout_width="0dp"
        android:layout_height="match_parent"
        android:background="@color/teal_200"
        app:layout_constraintStart_toEndOf="@+id/view1"
        app:layout_constraintWidth_percent="0.8" />


</androidx.constraintlayout.widget.ConstraintLayout>

To answer for the question conditions if no way to use ConstraintLayout:

Using android:layout_weight in a View that is wrapped in a RelativeLayout is prohibited as RelativeLayout doesn't provide that attribute for the underlying views (notice attributes start with layout_ are back to the parent layout which is RelativeLayout).

The same way, using android:layout_weight in aRelativeLayout that doesn't mean that it's back to the RelativeLayout itself, but to its parent layout which is already a LinearLayout

So, this will work normally either it's LinearLayout or a RelativeLayout:

<?xml version="1.0" encoding="utf-8"?>
 
<LinearLayout 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"
    android:baselineAligned="false"
    android:orientation="horizontal"
    android:weightSum="1">
 
    <LinearLayout
        android:layout_width="0dp"
        android:layout_height="match_parent"
        android:layout_weight="0.2"
        android:background="@color/teal_700" />
 
    <RelativeLayout
        android:layout_width="0dp"
        android:layout_height="match_parent"
        android:layout_weight="0.8"
        android:background="@color/teal_200">
 
        <TextView
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="This is some text in Relative Layout" />
 
    </RelativeLayout>
 
 
</LinearLayout>