How to evenly space out radiobuttons in Android?

If you want them to share screen width equally you need to set android:layout_width="match_parent" on each View. Your xml would become:

<RadioGroup
    android:id="@+id/auton_bar"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_below="@id/clear_fields"
    android:orientation="horizontal"
    android:paddingLeft="10dp" >

    <RadioButton
        android:id="@+id/auton_radio_1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:background="@drawable/auton_col" />
    <!-- android:layout_marginRight="380dp" -->

    <RadioButton
        android:id="@+id/auton_radio_2"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:background="@drawable/auton_col" />

    <RadioButton
        android:id="@+id/auton_radio_3"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:background="@drawable/auton_col" />
</RadioGroup>

To elaborate, layout_weight can be used in two ways.

• If you have multiple views in a vertical linear layout and you want the last one to take up all the remaining space, you can set their heights to wrap_content and give the last view a weight of 1.
• If you want all views to share the available space, set all width/heights to 0dp or match_parent and give each view the same weight value. They will share the space equally.

To have your background drawable scale, make a new xml that goes in your drawable/ folder that looks like this

<?xml version="1.0" encoding="utf-8"?>
<bitmap xmlns:android="http://schemas.android.com/apk/res/android"
    android:gravity="center"
    android:src="@drawable/auton_col" />

Name it whatever you like (e.g. auton_col_scale.xml) and reference that drawable as your background.

I noticed that using layout weights for the RadioButton's caused them to be aligned off-center, eventhough they definitely each shared 50% of the screen (they were left-aligned). Setting a gravity for each RadioButton caused only the text to be centered /facepalm

The XML below shows how to horizontally align two radiobuttons (could be any views) and center them:

                <RadioGroup
                    android:id="@+id/radiogroup"
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:orientation="horizontal">

                    <Space
                        android:layout_width="wrap_content"
                        android:layout_height="wrap_content"
                        android:layout_weight="1"/>

                    <RadioButton
                        android:id="@+id/radioyes"
                        android:layout_width="wrap_content"
                        android:layout_height="wrap_content"
                        android:text="@string/yes"
                        android:checked="false"/>

                    <Space
                        android:layout_width="wrap_content"
                        android:layout_height="wrap_content"
                        android:layout_weight="1"/>

                    <RadioButton
                        android:id="@+id/radiono"
                        android:layout_width="wrap_content"
                        android:layout_height="wrap_content"
                        android:text="@string/no"
                        android:checked="false"/>

                    <Space
                        android:layout_width="wrap_content"
                        android:layout_height="wrap_content"
                        android:layout_weight="1"/>

                </RadioGroup>

set width to match parent of each layout and then add weight jsut like linear layout.

<RadioGroup
            android:id="@+id/radio_group"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginStart="@dimen/bigMarginStart"
            android:layout_marginTop="@dimen/smallMarginTop"
            android:layout_marginEnd="@dimen/baseMarginEnd"
            android:orientation="horizontal"
            android:weightSum="3"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent">

            <RadioButton
                android:id="@+id/all_"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:layout_marginTop="@dimen/smallMarginTop"
                android:layout_weight="1"
                android:background="@drawable/radio_flat_selector"
                android:button="@android:color/transparent"
                android:checked="true"
                android:gravity="center"
                android:paddingLeft="@dimen/bigPaddingStart"
                android:paddingTop="@dimen/smallPaddingTop"
                android:paddingRight="@dimen/bigPaddingStart"
                android:paddingBottom="@dimen/smallPaddingBottom"
                android:text="All" />

            <RadioButton
                android:id="@+id/future_"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:layout_marginStart="@dimen/smallMarginStart"
                android:layout_marginTop="@dimen/smallMarginTop"
                android:layout_marginEnd="@dimen/smallMarginEnd"
                android:layout_weight="1"
                android:background="@drawable/radio_flat_selector"
                android:button="@android:color/transparent"
                android:gravity="center"
                android:paddingLeft="@dimen/bigPaddingStart"
                android:paddingTop="@dimen/smallPaddingTop"
                android:paddingRight="@dimen/bigPaddingStart"
                android:paddingBottom="@dimen/smallPaddingBottom"
                android:text="Future" />

            <RadioButton
                android:id="@+id/direct_"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:layout_marginTop="@dimen/smallMarginTop"
                android:layout_weight="1"
                android:background="@drawable/radio_flat_selector"
                android:button="@android:color/transparent"
                android:gravity="center"
                android:paddingLeft="@dimen/bigPaddingStart"
                android:paddingTop="@dimen/smallPaddingTop"
                android:paddingRight="@dimen/bigPaddingStart"
                android:paddingBottom="@dimen/smallPaddingBottom"
                android:text="Direct" />

        </RadioGroup>