Nested layout for android app is not working

Question

This is my XML file that I created. I am unable to set the LinearLayout's height. I have set the LinearLayout's orientation to horizontal and I have used layout_weight to set the height of LinearLayout.

However when I am setting the TextView's height to match_parent it doesn't work.

<RelativeLayout 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:paddingBottom="16dp"
    android:paddingLeft="16dp"
    android:paddingRight="16dp"
    android:paddingTop="16dp"
    tools:context=".MainActivity"
    android:weightSum="3">

    <LinearLayout 
        android:id="@+id/a"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1"
        android:orientation="horizontal">
        <TextView
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:text="1"/>
        <TextView
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:text="2"/>
    </LinearLayout>
    <LinearLayout 
        android:id="@+id/b"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1"
        android:orientation="horizontal"
        android:layout_below="@id/a">
        <TextView
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:text="3"/>
        <TextView
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:text="4"/>
    </LinearLayout>
    <LinearLayout 
        android:id="@+id/c"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1"
        android:orientation="horizontal"
        android:layout_below="@id/b">
        <TextView
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:text="5"/>
        <TextView
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:text="6"/>
    </LinearLayout>
</RelativeLayout>

Answer 1

It is not working because RelativeLayout (your root layout) does not support weights. So change your top level RelativeLayout to LinearLayout with vertical orientation and it should work.