Now that you have two implementations of
TabHelper
and
CompatTab
—one for Android 3.0 and later and one for earlier versions of the platform—it's time to do something with these implementations. This lesson discusses creating the logic for switching between these implementations, creating version-aware layouts, and finally using the backward-compatible UI component.
Add the Switching Logic
The
TabHelper
abstract class acts as a
factory
for creating version-appropriate
TabHelper
and
CompatTab
instances, based on the current device's platform version:
public abstract class TabHelper { ... // Usage is TabHelper.createInstance(activity) public static TabHelper createInstance(FragmentActivity activity) { if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) { return new TabHelperHoneycomb(activity); } else { return new TabHelperEclair(activity); } } // Usage is mTabHelper.newTab("tag") public CompatTab newTab(String tag) { if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) { return new CompatTabHoneycomb(mActivity, tag); } else { return new CompatTabEclair(mActivity, tag); } } ... }
Create a Version-Aware Activity Layout
The next step is to provide layouts for your activity that can support the two tab implementations. For the older implementation (
TabHelperEclair
), you need to ensure that your activity layout contains a
TabWidget
and
TabHost
, along with a container for tab contents:
res/layout/main.xml:
<!-- This layout is for API level 5-10 only. --> <TabHost xmlns:android="http://schemas.android.com/apk/res/android" android:id="@android:id/tabhost" android:layout_width="match_parent" android:layout_height="match_parent"> <LinearLayout android:orientation="vertical" android:layout_width="match_parent" android:layout_height="match_parent" android:padding="5dp"> <TabWidget android:id="@android:id/tabs" android:layout_width="match_parent" android:layout_height="wrap_content" /> <FrameLayout android:id="@android:id/tabcontent" android:layout_width="match_parent" android:layout_height="0dp" android:layout_weight="1" /> </LinearLayout> </TabHost>
For the
TabHelperHoneycomb
implementation, all you need is a
FrameLayout
to contain the tab contents, since the tab indicators are provided by the
ActionBar
:
res/layout-v11/main.xml:
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android" android:id="@android:id/tabcontent" android:layout_width="match_parent" android:layout_height="match_parent" />
At runtime, Android will decide which version of the
main.xml
layout to inflate depending on the platform version. This is the same logic shown in the previous section to determine which
TabHelper
implementation to use.
Use TabHelper in Your Activity
In your activity's
onCreate()
method, you can obtain a
TabHelper
object and add tabs with the following code:
@Override public void onCreate(Bundle savedInstanceState) { setContentView(R.layout.main); TabHelper tabHelper = TabHelper.createInstance(this); tabHelper.setUp(); CompatTab photosTab = tabHelper .newTab("photos") .setText(R.string.tab_photos); tabHelper.addTab(photosTab); CompatTab videosTab = tabHelper .newTab("videos") .setText(R.string.tab_videos); tabHelper.addTab(videosTab); }
When running the application, this code inflates the correct activity layout and instantiates either a
TabHelperHoneycomb
or
TabHelperEclair
object. The concrete class that's actually used is opaque to the activity, since they share the common
TabHelper
interface.
Below are two screenshots of this implementation running on an Android 2.3 and Android 4.0 device.