android中界面不能滚动如何解决

<TextView
        android:layout_width="fill_parent"
        android:layout_height="50px"
        android:text="This is head!!!"
        />
         <ExpandableListView 
            android:id="@id/android:list" 
            android:groupIndicator="@null"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:background="#808080"
            android:cacheColorHint="#00000000" 
            android:listSelector="@drawable/media"
    
            />
         <TextView 
            android:layout_width="fill_parent"
            android:layout_height="30px"
            android:text="This is foot!!"
           />