res/layout/message_view_subheader.xml

<?xml version="1.0" encoding="utf-8"?>
<!-- Copyright (C) 2011 The Android Open Source Project

     Licensed under the Apache License, Version 2.0 (the "License");
     you may not use this file except in compliance with the License.
     You may obtain a copy of the License at

          http://www.apache.org/licenses/LICENSE-2.0

     Unless required by applicable law or agreed to in writing, software
     distributed under the License is distributed on an "AS IS" BASIS,
     WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     See the License for the specific language governing permissions and
     limitations under the License.
-->

<!-- The expandable list of recipient addressese and date information at
     the top of a message view -->

<merge xmlns:android="http://schemas.android.com/apk/res/android">

    <!-- Collapsed version -->
    <LinearLayout
        xmlns:android="http://schemas.android.com/apk/res/android"
        android:id="@+id/sub_header_contents_collapsed"
        android:layout_width="match_parent"
        android:layout_height="48dip"
        android:gravity="center_vertical"
        >
        <!-- To, Cc, Bcc addresses -->
        <TextView
            android:id="@+id/addresses"
            android:layout_width="0dip"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:layout_marginLeft="8dip"
            android:singleLine="true"
            android:ellipsize="end"
            style="@style/message_view_text"
            />
        <TextView
            android:id="@+id/datetime"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginLeft="16dip"
            android:singleLine="true"
            style="@style/message_view_text"
            />
        <!--  Set proper background to reflect selected state -->
        <ImageView
            android:id="@+id/show_details"
            android:src="@drawable/expander_open_holo_light"
            android:layout_width="wrap_content"
            android:layout_height="48dip"
            android:layout_marginLeft="4dip"
            android:scaleType="center"
            android:background="?android:attr/selectableItemBackground"
            />
    </LinearLayout>

    <!-- Expanded version -->
    <FrameLayout
        android:id="@+id/sub_header_contents_expanded"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:visibility="gone"
        >

        <include layout="@layout/message_view_details" />

        <!-- Overlay the collapse details icon.
             The height here needs to match the height of the collapsed subheader -->
        <ImageView
            android:id="@+id/show_details"
            android:src="@drawable/expander_close_holo_light"
            android:layout_width="wrap_content"
            android:layout_height="48dip"
            android:layout_marginLeft="4dip"
            android:scaleType="center"
            android:layout_gravity="right"
            />
    </FrameLayout>

</merge>