Post 72: How to create evenly divided buttons that fills the entire space of the viewport on Android apps

I had to try different layout and read through several Stackoverflow posts until I could achieve what I wanted: buttons evenly spread on the viewport. At first I thought you can easily achieve that with a GridLayout. But no, you can achieve this with nested LinearLayout:

<?xml version="1.0" encoding="utf-8"?>
    <!--tools:showIn="@layout/activity_test_widget"-->
<android.support.constraint.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"
    app:layout_behavior="@string/appbar_scrolling_view_behavior"
    tools:context="test.TodoWidget">

    <LinearLayout
        android:layout_width="368dp"
        android:layout_height="439dp"
        android:orientation="vertical"
        app:layout_constraintVertical_weight="1"
        tools:layout_editor_absoluteY="8dp"
        tools:layout_editor_absoluteX="8dp">

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:orientation="horizontal">

            <EditText
                android:id="@+id/editTextTaskInput"
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:hint="test"
                android:ems="10"
                android:inputType="textMultiLine" />
        </LinearLayout>
        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_weight="1"
            app:layout_constraintHorizontal_weight="1"
            android:orientation="horizontal">

            <Button
                android:id="@+id/b1"
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:text="b1" />

            <Button
                android:id="@+id/b2"
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:text="b2" />
        </LinearLayout>
        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_weight="1"
            app:layout_constraintHorizontal_weight="1"
            android:orientation="horizontal">
            <Button
                android:id="@+id/b3"
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:text="b3" />
            <Button
                android:id="@+id/b4"
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:text="b4" />
        </LinearLayout>
    </LinearLayout>

    <android.support.design.widget.FloatingActionButton
        android:id="@+id/nextButton"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="@dimen/fab_margin"
        app:srcCompat="@android:drawable/ic_media_next"
        android:layout_weight="1"
        app:layout_constraintBottom_toBottomOf="parent"

        app:layout_constraintEnd_toEndOf="parent"
        tools:layout_editor_absoluteX="328dp" />

</android.support.constraint.ConstraintLayout>