Circle ViewPager indicators

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <android.support.v4.view.ViewPager
        android:id="@+id/pager"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>

    <LinearLayout
        android:id="@+id/circles"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginBottom="24dp"
        android:layout_gravity="center|bottom"
        android:gravity="center_vertical"
        android:orientation="horizontal">

    </LinearLayout>

</FrameLayout>

circle.xml

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="oval">
    <solid android:color="#49ffffff" />
    <size android:width="8dp" android:height="8dp"/>
</shape>

circle_selected.xml

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="oval">
    <solid android:color="#ffffffff" />
    <size android:width="10dp" android:height="10dp"/>
</shape>

MainActivity.java

public class MainActivity extends AppCompatActivity {
    
    // ...
    
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        
        // ... 
        
        mPager.setAdapter(mAdapter);
        mPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
            @Override
            public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
            }
    
            @Override
            public void onPageSelected(int position) {
                setIndicator(position);
            }
    
            @Override
            public void onPageScrollStateChanged(int state) {
    
            }
        });
    
        buildCircles();
        
        // ...
    }
    
    private void buildCircles(){
        float scale = getResources().getDisplayMetrics().density;
        int padding = (int) (5 * scale + 0.5f);
    
        for (int i = 0 ; i < mAdapter.getCount() ; i++) {
            ImageView circle = new ImageView(this);
            circle.setImageResource(R.drawable.circle);
            circle.setLayoutParams(new ViewGroup.LayoutParams(ViewGroup.LayoutParams.WRAP_CONTENT, ViewGroup.LayoutParams.WRAP_CONTENT));
            circle.setAdjustViewBounds(true);
            circle.setPadding(padding, 0, padding, 0);
            circles.addView(circle);
        }
    
        setIndicator(0);
    }
    
    private void setIndicator(int index){
        if (index < mAdapter.getCount()) {
            for (int i = 0 ; i < mAdapter.getCount() ; i++) {
                ImageView circle = (ImageView) circles.getChildAt(i);
                if (i == index) {
                    circle.setImageResource(R.drawable.circle_selected);
                } else {
                    circle.setImageResource(R.drawable.circle);
                }
            }
        }
    }
    
}