How to change Splash Screen Image on The Fly

I have an image that is shown at startup. I have a blank splash activity, with no layout and use a them to define the file that contains a layer-list. I want to find out what the image is and then swap it out on start. But I have no way of figuring out the image and what to grab to change it in the xml styles.

public class SplashActivity{

    Map<String, String> map = new HashMap<String, String>();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        // some code here to swap out the xml styles image with one I have stored elsewhere.
    }

....
}

AndroidManifest.xml

<activity
    android:name=".MySplashActivity"
    android:icon="@drawable/ic_launcher"
    android:label="@string/app_name"
    android:theme="@style/MyTheme">
    <intent-filter>
        <action android:name="android.intent.action.MAIN" />
        <category android:name="android.intent.category.LAUNCHER" />
    </intent-filter>

Styles.xml

<style name="MyTheme" parent="Theme.AppCompat.NoActionBar">
    <item name="android:windowBackground">@drawable/splash_screen_image</item>
</style>

Splash_screen_image.xml

<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
    <item>
        <shape android:shape="rectangle">
            <gradient android:angle="0" android:startColor="@color/primary_bright" android:endColor="@color/primary_medium" />
        </shape>
    </item>
    <item>
        <!-- This is the image that needs to change on the fly -->
        <bitmap
            android:gravity="center"
            android:src="@drawable/image_cars_logo"/>
    </item>

</layer-list>