How to change fontFamily of TextView in Android

So I'd like to change the android:fontFamily in Android but I don't see any pre-defined fonts in Android. How do I select one of the pre-defined ones? I don't really need to define my own TypeFace but all I need is something different from what it shows right now.

    android:id="@+id/HeaderText"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentTop="true"
    android:layout_centerHorizontal="true"
    android:layout_marginTop="52dp"
    android:gravity="center"
    android:text="CallerBlocker"
    android:textSize="40dp"
    android:fontFamily="Arial"

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It seems what I did up there won't really work! BTW android:fontFamily="Arial" was a stupid attempt!

Answer

From android 4.1 / 4.2 / 5.0, the following Roboto font families are available:

android:fontFamily="sans-serif"           // roboto regular
android:fontFamily="sans-serif-light"     // roboto light
android:fontFamily="sans-serif-condensed" // roboto condensed

android:fontFamily="sans-serif-black"     // roboto black
android:fontFamily="sans-serif-thin"      // roboto thin (android 4.2)
android:fontFamily="sans-serif-medium"    // roboto medium (android 5.0)

in combination with

android:textStyle="normal|bold|italic"

this 16 variants are possible:

• Roboto regular


• Roboto italic


• Roboto bold


• Roboto bold italic


• Roboto-Light



• Roboto-Light italic


• Roboto-Thin


• Roboto-Thin italic


• Roboto-Condensed


• Roboto-Condensed italic


• Roboto-Condensed bold


• Roboto-Condensed bold italic


• Roboto-Black


• Roboto-Black italic


• Roboto-Medium



• Roboto-Medium italic

fonts.xml

    sans-serif-light
    sans-serif-medium
    sans-serif

    sans-serif-condensed
    sans-serif-black
    sans-serif-thin