Extend color background in Android Studio

Question

I started to work with Android Studio, i created a small app and set background:

android:background="#3F51B5"

but when i run the emulator i see a lower white/dark band, specially in smartphone with larger displays

what can i do?

i use linear layout and one section with constraintlayout. the first portion of main activity is

<LinearLayout 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="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentStart="false"
android:background="#3F51B5"
android:orientation="vertical"
android:paddingLeft="16dp"
android:paddingRight="16dp"
tools:context=".MainActivity"
tools:visibility="visible">

Answer 1

do like this:

android:layout_width="match_parent"
android:layout_height="match_parent"

with this way you can fill all the display with the color that you choose

Answer 2

If you wish to keep your LinearLayout as is but the full background as the colour you want, then I suggest wrapping this in a ConstraintLayout whose width and length can be match parent, or height can be wrap content as per your need

<androidx.constraintlayout.widget.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android" 
    xmlns:app="http://schemas.android.com/apk/res-auto"
    
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#3F51B5">

    <LinearLayout 
           xmlns:tools="http://schemas.android.com/tools"       
           android:layout_width="wrap_content"
           android:layout_height="wrap_content"
           android:layout_alignParentStart="false"
           
           android:orientation="vertical"
           android:paddingLeft="16dp"
           android:paddingRight="16dp"
           tools:context=".MainActivity"
           tools:visibility="visible"> 
           //Views 
     </LinearLayout>

</androidx.constraintlayout.widget.ConstraintLayout>