gradient_1.xmlgradient_2.xmlgradient_3.xmlgradient_list.xmlactivity_main.xmlMainActivity.java
<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android">
    <gradient
        android:angle="225"
        android:endColor="#044fab"
        android:startColor="#ffd6d3" />
</shape>

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android">
    <gradient
        android:angle="135"
        android:endColor="#43b4ef"
        android:startColor="#32ff3f" />
</shape>

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android">
    <gradient
        android:angle="45"
        android:endColor="#933c94"
        android:startColor="#517f95" />
</shape>

<?xml version="1.0" encoding="utf-8"?>
<animation-list xmlns:android="http://schemas.android.com/apk/res/android">

    <item android:drawable="@drawable/gradient_1"
        android:duration="4000"/>

    <item android:drawable="@drawable/gradient_2"
        android:duration="4000"/>

    <item android:drawable="@drawable/gradient_3"
        android:duration="4000"/>

</animation-list>

<?xml version="1.0" encoding="utf-8"?>
<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:id="@+id/layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@drawable/gradient_list"
    tools:context="com.example.application.animatedgradientapp.MainActivity">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World!"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</android.support.constraint.ConstraintLayout>

package com.example.application.animatedgradientapp;

import android.graphics.drawable.AnimationDrawable;
import android.support.constraint.ConstraintLayout;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        ConstraintLayout constraintLayout = findViewById(R.id.layout);
        AnimationDrawable animationDrawable = (AnimationDrawable) constraintLayout.getBackground();
        animationDrawable.setEnterFadeDuration(2000);
        animationDrawable.setExitFadeDuration(4000);
        animationDrawable.start();
    }
}