What is the baseline in RelativeLayout?

Question

What does "baseline" refer to when used in the context of a relative layout? Simple question, probably, but the documentation and google offer no hints.

Answer 1

The term baseline comes from typography. It's the invisible line letters in text sit on.

For example, imagine you put two TextView elements next to each other. You give the second TextView a big padding (say 20dp). If you add layout_alignBaseline to the second element, the text will "scoot up" to align with the baseline of the first element. The text from both elements will appear as if they were written on the same invisible line.

<RelativeLayout
    android:layout_width="fill_parent"
    android:layout_height="fill_parent" >
  <TextView
      android:id="@+id/text1"
      android:text="aatlg"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      />
  <TextView
      android:text="joof"
      android:background="#00ff00"
      android:padding="20dp"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_toRightOf="@id/text1"
      android:layout_alignBaseline="@id/text1"
      />
</RelativeLayout>