Creating a horizontal rule (line) in Android

Use a View with fixed height -

 android:layout_width="fill_parent"
 android:layout_height="2dip"
 android:background="#FF00FF00" />

or, in code -

View ruler = new View(myContext); ruler.setBackgroundColor(0xFF00FF00);
theParent.addView(ruler,
 new ViewGroup.LayoutParams( ViewGroup.LayoutParams.FILL_PARENT, 2));

Source – Romain Guy