Shadow beneath Android TextView -

i've been trying add shadow effect beneath textview, reason, it's not working! layout xml given below. can please find out reason that?

<textview     android:id="@+id/textview1"     android:text="hello world!"     android:layout_width="wrap_content"     android:layout_height="wrap_content"     android:layout_alignparentbottom="true"     android:layout_alignparentleft="true"     android:layout_alignparentright="true"     android:layout_alignparenttop="true"     android:background="@drawable/myshape"     android:shadowcolor="#ff0000"       android:shadowradius="3"       android:shadowdx="2"       android:shadowdy="2"     android:gravity="center"     android:textappearance="?android:attr/textappearancemedium" /> 

myshape drawable:

    <?xml version="1.0" encoding="utf-8"?> <shape      xmlns:android="http://schemas.android.com/apk/res/android" >     android:shape=["rectangle"] >   <stroke     android:width="2dp"     android:color="#ffffffff" />   <gradient     android:endcolor="#ddbbbbbb"     android:startcolor="#dd777777"     android:angle="90" />   <corners     android:bottomrightradius="15dp"     android:bottomleftradius="15dp"     android:topleftradius="15dp"     android:toprightradius="15dp" />  </shape>