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!!"           />