Rendering Issues on Android Activity

Question

I've a sample Login activity like below. But Why am I getting the Rendering issues?

When I try to refresh the screen, there is a layover like below.

How can I fix this?

Here is my code

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
>

<TextView android:text="Login With Facebook"

    android:id="@+id/btnLogin"
    android:padding="16dp"
    android:layout_centerInParent="true"
    android:background="#494949"
    android:textColor="#fff"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content" />

<com.facebook.login.widget.LoginButton
    android:visibility="gone"
    android:id="@+id/login_button"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_gravity="center_horizontal"
    android:layout_marginTop="30dp"
    android:layout_marginBottom="30dp" />

</RelativeLayout>