Positions Relative to Container
The easiest relations to set up are tying a widget’s position to that of its container:
1. android:layout_alignParentTop says the widget’s top should align with the
top of the container
2. android:layout_alignParentBottom says the widget’s bottom should align
with the bottom of the container
3. android:layout_alignParentLeft says the widget’s left side should align
with the left side of the container