fill_parent、wrap_content、match_parent 用法实例测试
fill_parent设置一个顶部布局或控件强制性让它布满整个屏幕。
wrap_content布局指根据视图内部内容自动扩展以适应其大小，（刚好能支撑起其内容的大小）
Android2.2后fill_parent由match_parent替代。
Note: Beginning with Android 2.2 (API level 8),
"fill_parent"has been renamed"match_parent"to better reflect the behavior. The reason is that if you set a view to"fill_parent"it does not expand to fill the remaining space after sibling views are considered, but instead expands tomatch the size of the parent view no matter what—it will overlap any sibling views.
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/button_send" />
<Button
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="@string/button_send" />
<Button
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:text="@string/button_send" />
<Button
android:layout_width="match_parent"
android:layout_height="match_parent"
android:text="@string/button_send" />
REF:http://blog.csdn.net/jumping_android/article/details/7397991