Gradient in xml doesn’t occur on a button

I created a gradient in my Drawable Resource File (.xml) and then connected it to button’s (in activity_main.xml) background. Unfortunately, all structures in this file didn’t occur on this button. I am a beginner. Is this problem with the code or something else? The gradient works as an ImageView and even as a Switch but does not work as a button’s background. Code from gradient.xml:

<?xml version="1.0" encoding="UTF-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android" android:shape="rectangle" >
    <item>
        <shape>
              <gradient
                   android:angle="90"
                   android:endColor="#b5b6d2"
                   android:startColor="#555994"
                   android:type="linear" />
               <corners
                   android:radius="0dp"/>
               <padding
                   android:right="10dp"
                   android:top="10dp"
                   android:bottom="10dp"
                   android:left="10dp"/>
        </shape>
    </item>
</selector>

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.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:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <Button
        android:id="@+id/button2"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginStart="16dp"
        android:layout_marginLeft="16dp"
        android:layout_marginTop="16dp"
        android:layout_marginEnd="16dp"
        android:layout_marginRight="16dp"
        android:background="@drawable/gradient"
        android:text="@string/button"
        android:textColor="@android:color/white"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>

Answer

You use selector when you want to show different background / color according to different states of the widget . For your case replace your code with this code in your drawable file :

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
  android:shape="rectangle">
<gradient
    android:angle="90"
    android:endColor="#b5b6d2"
    android:startColor="#555994"
    android:type="linear" />
<corners
    android:radius="0dp"/>

</shape>

Correction : The Button widget is taking colorAccent as default background strangely change the widget to AppCompatButton and it will solve the problem .

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.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:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <androidx.appcompat.widget.AppCompatButton
        android:id="@+id/button2"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginStart="16dp"
        android:layout_marginLeft="16dp"
        android:layout_marginTop="16dp"
        android:layout_marginEnd="16dp"
        android:layout_marginRight="16dp"
        android:text="Button"
        android:background="@drawable/gradient"
        android:textColor="@android:color/white"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>