How to Set Scroll View to this XML File?

I'm beginner in android and write this code for my activity XML file:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://ift.tt/nIICcg"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:weightSum="4"
    >
    <ImageView
        android:id="@+id/ExplainImage"
        android:layout_gravity="center"
        android:layout_width="fill_parent"
        android:layout_height="0dp"
        android:layout_weight="1"
        android:src="@drawable/abc_btn_check_material">
    </ImageView>

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="0dp"
        android:textAppearance="?android:attr/textAppearanceLarge"
        android:text="Large Text"
        android:id="@+id/MAINLABEL"
        android:layout_weight="3"
        android:layout_gravity="center"
        android:height="2dp" />
  </LinearLayout>

and show and work good,but i want scroll text view in big text and change text view part to this:

<ScrollView
        xmlns:android="http://ift.tt/nIICcg"
        android:layout_height="fill_parent"
        android:layout_width="fill_parent"
        >
    <TextView
        android:layout_width="wrap_content"
        android:layout_height="0dp"
        android:textAppearance="?android:attr/textAppearanceLarge"
        android:text="Large Text"
        android:id="@+id/MAINLABEL"
        android:layout_weight="3"
        android:layout_gravity="center"
        android:height="2dp" />
   </ScrollView>

but not show text to me or image,what happen?how can i solve that?thanks.