Actually THERE IS a way to prevent hint from hiding, and it's a cool one :-)
It gives you the Floating Label look with smooth animation very easily and it's from android itself. No extra libraries and stuff.
Try this:
<android.support.design.widget.TextInputLayout
android:layout_width="match_parent"
android:layout_height="wrap_content">
<EditText
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:hint="Touch me and I'll fly!"/>
</android.support.design.widget.TextInputLayout>
You can change the behaviour using other xml tags like android:gravity="start|center|end"
and others.
As a BONUS, you can use error messages with it :-) Here's the link to that question: https://stackoverflow.com/a/30953551/6474744
And sorry I do not have enough reputatuion to post images, so help yourself:
http://i0.wp.com/androidlift.info/wp-content/uploads/2015/09/Screenshot_2015-09-28-17-03-561.png
Enjoy :-)