align：对齐
常用属性：
layout_toRightOf：在**的右边
android:layout_toRightOf="@+id/view_3"
-------------------------------------------------------
layout_alignBottom：底部和**对齐
android:layout_alignBottom="@+id/view_3"
-------------------------------------------------------
layout_below:在**下面
android:layout_below="@+id/ll_1"
-------------------------------------------------------
layout_alignParentTop：与外部容器的顶部对齐
android:layout_alignParentTop="true"
-------------------------------------------------------
原文：https://www.cnblogs.com/AppTester/p/9907665.html