Linear Layout

LinearLayout  aligns all view (TextView, Button and more ) in a single direction, vertically or horizontally. You can specify the layout direction with the android:orientation attribute.

Code -

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

 android:orientation="vertical" 

android:layout_width="match_parent"

android:layout_height="match_parent">

</LinearLayout>

Weight_sum :  Weight Sum is used in Linear Layout to specify  a different -2 weight to child attribute.

android:layout_weight  should be equal to weight sum.

Layout_Weight :  This attribute specify that  how much space view ( textview or buttn or any other ) should occupy on the screen.

weight_sum = layout_weight + layout_weight +  layout_weight + ...

weight_sum is declare inside the parent attribute and layout_weight is set in child attribute.

Example -

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

    android:layout_width="match_parent"

    android:layout_height="match_parent"

    android:paddingLeft="16dp"

    android:paddingRight="16dp"

    android:baselineAligned="true"

    android:orientation="horizontal"

    android:weightSum="2"

    >

    <LinearLayout

        android:layout_width="0dp"

        android:layout_height="wrap_content"

        android:layout_weight="1.25"

        android:orientation="vertical"

        >

    <EditText

        android:layout_width="match_parent"

        android:layout_height="wrap_content"

        android:hint="to" />

    <EditText

        android:layout_width="match_parent"

        android:layout_height="wrap_content"

        android:hint="subject" />

    <EditText

        android:layout_width="match_parent"

        android:layout_height="0dp"

        android:layout_weight="1"

        android:gravity="top"

        android:hint="message" />

    <Button

        android:layout_width="100dp"

        android:layout_height="wrap_content"

        android:layout_gravity="right"

        android:text="send" />

    </LinearLayout>

    <LinearLayout

        android:layout_width="0dp"

        android:layout_height="wrap_content"

        android:layout_weight="0.75"

        android:orientation="vertical"

        android:background="#C8CCCC"

        >

        <EditText

            android:layout_width="match_parent"

            android:layout_height="wrap_content"

            android:hint="to" />

        <EditText

            android:layout_width="match_parent"

            android:layout_height="wrap_content"

            android:hint="subject" />

        <EditText

            android:layout_width="match_parent"

            android:layout_height="0dp"

            android:layout_weight="1"

            android:gravity="top"

            android:hint="message" />

        <Button

            android:layout_width="100dp"

            android:layout_height="wrap_content"

            android:layout_gravity="right"

            android:text="send" />

    </LinearLayout>

</LinearLayout>