can't get reference to item inside of layer-list

Question

I want to get a reference to item inside of the layer-list for changing some attributes programmatically, But I can't see any difference and seems it does not work.

this is my code:

logo.xml

<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
<item android:id="@+id/circle">
    <shape android:shape="oval">
        <solid android:color="#fff"/>
        <size android:height="33px" android:width="33px"/>
        <stroke android:color="#000" android:width="2px"/>
    </shape>
</item>
</layer-list>

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:id="@+id/activity_main"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.example.shahin.testing2.MainActivity">

<Button
    android:layout_width="33px"
    android:id="@+id/button"
    android:layout_height="33px"
    android:background="@drawable/logo"/>
  </LinearLayout>

MainActivity.java

    @Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    LayerDrawable layerDrawable = (LayerDrawable) 
    ContextCompat.getDrawable(getApplicationContext(),R.drawable.logo);
    GradientDrawable gradientDrawable = (GradientDrawable) 
    layerDrawable.findDrawableByLayerId(R.id.circle);
    gradientDrawable.setStroke(10, Color.BLUE);
    Button button = (Button)findViewById(R.id.button);
    button.setBackgroundResource(R.drawable.logo);
}

in this case, when I changed the stroke color and width, no difference has appeared, what is the problem?