Android Linear Layout

Android LinearLayout is a view group that aligns all children in either vertically or horizontally.
Following are the important attributes specific to LinearLayout −
android:id
This is the ID which uniquely identifies the layout.
android:baselineAligned
This must be a boolean value, either "true" or "false" and prevents the layout from aligning its children's baselines.
android:baselineAlignedChildIndex
When a linear layout is part of another layout that is baseline aligned, it can specify which of its children to baseline align.
android:divider
This is drawable to use as a vertical divider between buttons. You use a color value, in the form of "#rgb", "#argb", "#rrggbb", or "#aarrggbb".
android:gravity
This specifies how an object should position its content, on both the X and Y axes. Possible values are top, bottom, left, right, center, center_vertical, center_horizontal etc.
android:orientation
This specifies the direction of arrangement and you will use "horizontal" for a row, "vertical" for a column. The default is horizontal.
android:weightSum
Sum up of child weight
This example will take you through simple steps to show how to create your own Android application using Linear Layout. Follow the following steps to modify the Android application we created in Hello World Example chapter −
Following is the content of the modified main activity file src/com.example.demo/MainActivity.java. This file can include each of the fundamental lifecycle methods.
package com.example.demo;

import android.os.Bundle;
import android.app.Activity;

public class MainActivity extends Activity {
   @Override
   protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);
   }
}
Following will be the content of res/layout/activity_main.xml file −
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
   android:layout_width="fill_parent"
   android:layout_height="fill_parent"
   android:orientation="vertical" >
   
   <Button android:id="@+id/btnStartService"
      android:layout_width="270dp"
      android:layout_height="wrap_content"
      android:text="start_service"/>
      
   <Button android:id="@+id/btnPauseService"
      android:layout_width="270dp"
      android:layout_height="wrap_content"
      android:text="pause_service"/>
      
   <Button android:id="@+id/btnStopService"
      android:layout_width="270dp"
      android:layout_height="wrap_content"
      android:text="stop_service"/>
      
</LinearLayout>
Following will be the content of  res/values/strings.xml to define two new constants −
<?xml version="1.0" encoding="utf-8"?>
<resources>
   <string name="app_name">HelloWorld</string>
   <string name="action_settings">Settings</string>
</resources>
Let's try to run our modified Hello World! application we just modified. I assume you had created your AVD while doing environment setup. To run the app from Android studio, open one of your project's activity files and click Run  icon from the toolbar. Android studio installs the app on your AVD and starts it and if everything is fine with your setup and application, it will display following Emulator window −
Now let's change the orientation of Layout as android:orientation="horizontal" and try to run the same application, it will give following screen −

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