Updated Dec 12 2012
It has been over a year since the ViewPager launched and in that time it’s been used by many developers to improve the user experience of their applications. Over the year the APIs have been updated, adding some new features and deprecating some old method signatures.
ViewPager
Five methods in PagerAdapter have been deprecated in order to switch from using View in the method signature to using ViewGroup. This makes it more obvious what the parameter refers to, improves the readability of the code and removes the need to constantly cast the Views to ViewGroups.
PagerAdapter
View
ViewGroup
Some official ViewPager resources have also been added:
A few ViewPager hints that are worth mentioning as they keep recurring are:
setOffscreenPageLimit(2)
Views
notifyDataSetChanged()
setPageMargin()
setPageMarginDrawable()
Here’s to the next year of paging views. The updated original post follows...
Whether you have just started out in Android app development or are a veteran of the craft, it probably won’t be too long before you’ll need to implement horizontally scrolling sets of views. Many existing Android apps already use this UI pattern. ViewPager standardizes the implementation.
ViewPager was released as part of the Compatibility Package revision 3 and works with Android 1.6 upwards. After following the instructions to obtain the package you can right-click on your Android project in Eclipse, choose ‘Android Tools’ and ‘Add Compatibility Library’, making the new classes available.
ViewPager is a ViewGroup and works in a similar manner to AdapterViews (like ListView and Gallery) so it shouldn’t feel too foreign. Note that if you use ViewPager in an xml layout, be sure to use the full class reference, e.g.
<android.support.v4.view.ViewPager android:layout_width="match_parent" android:layout_height="match_parent" … />
ViewPagers source their views from PagerAdapters which give you have full control over the reuse and recycling of the views. A PagerAdapter implementation called FragmentPagerAdapter is provided to facilitate the use of Fragments in a ViewPager; This is immensely powerful and as simple as implementing getCount() and getItem(). There is a sample called Fragment Pager Support provided in the Support Demos to illustrate this.
public static class MyAdapter extends FragmentPagerAdapter { public MyAdapter(FragmentManager fm) { super(fm); } @Override public int getCount() { return NUM_ITEMS; } @Override public Fragment getItem(int position) { return ArrayListFragment.newInstance(position); } }
FragmentPagerAdapter will detach each fragment as you swipe through the list, but keep them in memory so they can simply be reattached when the user swipes back. If you have a larger number of Fragments, the FragmentStatePagerAdapter is worth considering as it will remove them, with the downside being they need to be rebuilt as the user swipes back to them. So, if you have fewer, more complex fragments the FragmentPagerAdapter makes sense, but consider FragmentStatePagerAdapter for larger sets.
On the more simplistic side I recently wrote a ViewPager/PagerAdapter example that serves up simple TextViews. One thing to note is that if you are implementing your own PagerAdapter it is up to you, the developer, to add and remove your views to and from the ViewGroup. To facilitate this the ViewPager is passed into the PagerAdapter methods instantiateItem() and destroyItem().
@Override public Object instantiateItem(ViewGroup collection, int position) { View v = layoutInflater.inflate(...); ... ((ViewPager) collection).addView(v,0); return v; } @Override public void destroyItem(ViewGroup collection, int position, Object view) { ((ViewPager) collection).removeView((TextView) view); }
The source code for ViewPager is also included and available in <android-sdk>/extras/android/compatibility/v4/src. It is worth checking as you can generate the reference documentation from it using Javadoc. In the reference docs / source you’ll find other useful methods, for example setOnPageChangeListener(), which enables your application to track which View is currently visible.
[This post is by Ambarish Kenghe, who’s a Product Manager for Google TV — Tim Bray]
While the add-on does not contain all features of Google TV, it enables developers to emulate Google TV and build apps using standard Android SDK tools. It also provides new APIs for TV interaction, such as TV channel line-up. Google TV emulation is currently supported on Linux with KVM only, and we are working on support for other operating systems. We’re very happy that through KVM we’ve been able to create a fast Android emulator for TV.
Depending on the design and use case, an existing Android app may work well on Google TV as is, or it may require fixes. With the add-on you can test your apps to determine if they would be a good fit for TV and whether any tweaks are required. We are also publishing UI guidelines to help you with topics like optimizing for D-pad navigation, presenting information for 10-foot viewing, designing apps that work well across devices, etc. The guidelines include information on how certain UI elements on Google TV differ from other Android devices.
As with other devices, apps that require features not supported on Google TV won’t appear in Android Market on Google TV. For example, Google TV-based devices do not have a touchscreen; hence apps which require touchscreen will not appear. Conversely, if the manifest says touchscreen is not required, the app will appear. Please follow our guidelines carefully.
These are still early days for Google TV, and this release is another step in providing developer tools for the big screen. While the number of apps available on TV will initially be small, we expect that through this early release of the add-on you'll be able to bring optimized TV apps into the ecosystem more quickly. To start doing this, download the Google TV add-on today. Also, please continue to reach out to us on the Google TV Android Developer Community forum. We look forward to your contributions!
We in Android Developer Relations have been cooking up a rather special set of Android Developer Labs (ADLs) for the second half of 2011, and we’re ready to start the ball rolling.
Here’s the schedule. These are one-day events, so in Seattle and New York we’re running it twice for two audiences.
Bangalore — August 2 (happening today)
Seattle — August 15 and 16
New York — August 23 and 24
Los Angeles — September 2
This ADL series isn’t another set of introduction-to-Android sessions, nor any other kind of general overview. It's specifically aimed at optimizing Android apps for tablets, in particular creating high-quality tablet apps with an emphasis on polish and user-experience.
Registration is a two-step process. Anyone can register, but we can only accommodate a relatively small number of attendees from among the registrants, based on whether they already have an Android app with the potential to be a top-tier tablet app in terms of quality, fit, and finish. The goal is to bring your app to the ADL, and leave equipped to make it into one that makes Android tablet users smile.
Do you think you qualify? Sign up and show us!
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