I started a new Android Application based on master/detail flow template using ADT Eclipse. This template creates two activities, a master fragment and a detail fragment in order to fit small and larger screens.
I noticed the activity_item_list.xml file has the tools:layout attribute:
<fragment xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/item_list"
android:name="com.example.fragmenttwopanel.ItemListFragment"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_marginLeft="16dp"
android:layout_marginRight="16dp"
tools:context=".ItemListActivity"
tools:layout="@android:layout/list_content" />
I tried to delete the attribute and the app runs in the same way but in the graphical layout tab of ADT, a message ask me for:
pick preview layout from the "Fragment Layout" context menu
What is its purpose? Is it just for preview in graphical layout?
This is a namespace used by the IDE tools. This is not needed to run the application on a device (or emulator). On the other hand, if you leave them, Android will ignore them when the application is running on a device.
This is used by e.g. lint and graphical layout tab.
You can check how it's used by lint here: http://developer.android.com/tools/debugging/improving-w-lint.html in section Configuring lint checking in XML.
Yes, it's just information for the Graphical Layout editor how the fragment should be displayed in the editor.
Generally the tools attributes (with tools namespace prefix declared with xmlns:tools="http://schemas.android.com/tools") are used by the development tools and are not compiled in the application itself.
right click on the grey area, " fragment layout->choose layout" and select your layout , DONE!
来源：https://stackoverflow.com/questions/19136163/whats-toolslayout-in-fragment-xml-file