您如何确定在多个布局之间切换的活动最后使用哪种布局？

Question

I'm just starting to use fragments in my app and the idea is one column for screens of a certain width (or less) and two for wider screens. So I have two separate layout files and in the onCreate method of MainActivity I choose which one to show based on the screen width. Since I am interested in the screen width rather than the orientation I can't use the simpler option of 'layout-land'. Both layouts use the same fragments but they can't be hard coded into the layout files because some of them need to be add added and removed at runtime - thus I use a fragment transaction in the onCreate method to (at the moment) just add the fragments.

The problem comes when the activity is destroyed and recreated. If I don't check for whether savedinstancestate is null, it adds the fragments again (which is to be expected) and everything is doubled up. But if I only do the create code when it's null - as you would if there was only one layout - then when I test screen width again and just use setContentView(one or the other layout) it recreates the one that was shown with no problem but the other is blank. Again that's to be expected because the second one hasn't been instantiated yet. So is it possible to determine from the savedinstancestate which layout was in use when the activity was destroyed? And if it is, is it possible (or safe) to use the information in that to create the other layout - or should I just run the create code again? In other words does the standard savedinstancestate persist all the data I need when more than one layout is in use or will I have to do it all myself?

Answer 1

You can still use resource buckets to contain your layouts. ie:

use / layout-sw600dp / that is layout smallest width of 600 dip

From the official documentation http://developer.android.com/training/multiscreen/screensizes.html#TaskUseSWQuali

res/layout/main.xml, single-pane (default) layout:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <fragment android:id="@+id/headlines"
              android:layout_height="fill_parent"
              android:name="com.example.android.newsreader.HeadlinesFragment"
              android:layout_width="match_parent" />
</LinearLayout>

res/layout-sw600dp/main.xml, two-pane layout:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="horizontal">
    <fragment android:id="@+id/headlines"
              android:layout_height="fill_parent"
              android:name="com.example.android.newsreader.HeadlinesFragment"
              android:layout_width="400dp"
              android:layout_marginRight="10dp"/>
    <fragment android:id="@+id/article"
              android:layout_height="fill_parent"
              android:name="com.example.android.newsreader.ArticleFragment"
              android:layout_width="fill_parent" />
</LinearLayout>