Background for button not updating

In my Android project, I have a button with a background of purple, but it is showing blue.

This is my code:

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:orientation="vertical"
    android:gravity="center"
    android:background="@drawable/background_gradient"
    tools:context=".MainActivity">

    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_margin="50dp"
        android:background="@color/blue">

        <Button
            android:id="@ id/Button_StartGame"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:background="@color/purple"
            android:layout_margin="10dp"
            android:text="@string/start_game" />

    </RelativeLayout>
    
</LinearLayout>

colors.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <color name="lawnGreen">#7CFC00</color>
    <color name="neonGreen">#39FF14</color>
    <color name="cyan">#00FFFF</color>
    <color name="blue">#0000FF</color>
    <color name="yellow">#FFFF00</color>
    <color name="purple">#800080</color>
    <color name="pink">#EE82EE</color>
    <color name="black">#000000</color>
    <color name="white">#FFFFFF</color>
</resources>

themes.xml

<resources xmlns:tools="http://schemas.android.com/tools">
    <!-- Base application theme. -->
    <style name="Theme.MultiSmart" parent="Theme.MaterialComponents.DayNight.NoActionBar">
        <!-- Primary brand color. -->
        <item name="colorPrimary">@color/blue</item>
        <item name="colorPrimaryVariant">@color/purple</item>
        <item name="colorOnPrimary">@color/white</item>
        <!-- Secondary brand color. -->
        <item name="colorSecondary">@color/blue</item>
        <item name="colorSecondaryVariant">@color/purple</item>
        <item name="colorOnSecondary">@color/black</item>
        <!-- Status bar color. -->
        <item name="android:statusBarColor" tools:targetApi="l">?attr/colorPrimaryVariant</item>
        <!-- Customize your theme here. -->
    </style>
</resources>

themes.xml (night)

<resources xmlns:tools="http://schemas.android.com/tools">
    <!-- Base application theme. -->
    <style name="Theme.MultiSmart" parent="Theme.MaterialComponents.DayNight.NoActionBar">
        <!-- Primary brand color. -->
        <item name="colorPrimary">@color/blue</item>
        <item name="colorPrimaryVariant">@color/purple</item>
        <item name="colorOnPrimary">@color/black</item>
        <!-- Secondary brand color. -->
        <item name="colorSecondary">@color/blue</item>
        <item name="colorSecondaryVariant">@color/purple</item>
        <item name="colorOnSecondary">@color/black</item>
        <!-- Status bar color. -->
        <item name="android:statusBarColor" tools:targetApi="l">?attr/colorPrimaryVariant</item>
        <!-- Customize your theme here. -->
    </style>
</resources>

I didn't provide MainActivity.java because I didn't customize it yet, it's just a new project.

How can I fix this?

CodePudding user response：

Cause:

The android:background doesn't show up the right color in the button because when using a material components theme; there is a default tint color applied (i.e. it's not null like in the previous AppCompat themes), and it affects the button color.

Solution:

You can solve this by applying one of a couple of ways to the button:

Use android:backgroundTint instead of android:background
Set the tint to null with app:backgroundTint="@null", and normally use android:background