anroid的Button的边框圆角效果

<Button
android:id="@+id/start_edit_btn"
android:layout_width="match_parent"
android:layout_height="48dp"
android:layout_marginLeft="10dp"
android:layout_weight="1"
android:background="@drawable/sdk_sample_rect_btn_disable"
android:textColor="#444444"
android:gravity="center"
android:onClick="startEdit"
android:text="@string/pg_sdk_edit_sample_edit">
</Button>

<?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="#ffffff"/>
<corners android:radius="20dp"/>
</shape>