This lesson teaches you to
- Implement Swipe Views
- Add Tabs to the Action Bar
- Change Tabs with Swipe Views
- Use a Title Strip Instead of Tabs
You should also read
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EffectiveNavigation.zip
Swipe views provide lateral navigation between sibling screens such as tabs with a horizontal finger gesture (a pattern sometimes known as horizontal paging). This lesson teaches you how to create a tab layout with swipe views for switching between tabs, or how to show a title strip instead of tabs.
Swipe View Design
Before implementing these features, you should understand the concepts and recommendations as described in Designing Effective Navigation and the Swipe Views design guide.
Implement Swipe Views
You can create swipe views in your app using the ViewPager
widget, available in the
Support Library. The
ViewPager
is a layout widget in which each child view is
a separate page (a separate tab) in the layout.
To set up your layout with ViewPager
, add a
<ViewPager>
element to your XML layout. For example, if each page in the swipe view
should consume the entire layout, then your layout looks like this:
<?xml version="1.0" encoding="utf-8"?> <android.support.v4.view.ViewPager xmlns:android="http://schemas.android.com/apk/res/android" android:id="@+id/pager" android:layout_width="match_parent" android:layout_height="match_parent" />
To insert child views that represent each page,
you need to hook this layout to a PagerAdapter
.
There are two kinds of adapter you can use:
FragmentPagerAdapter
- This is best when navigating between sibling screens representing a fixed, small number of pages.
FragmentStatePagerAdapter
- This is best for paging across a collection of objects for which the number of pages is undetermined. It destroys fragments as the user navigates to other pages, minimizing memory usage.
For example, here's how you might use FragmentStatePagerAdapter
to swipe across a collection of Fragment
objects:
public class CollectionDemoActivity extends FragmentActivity { // When requested, this adapter returns a DemoObjectFragment, // representing an object in the collection. DemoCollectionPagerAdapter mDemoCollectionPagerAdapter; ViewPager mViewPager; public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_collection_demo); // ViewPager and its adapters use support library // fragments, so use getSupportFragmentManager. mDemoCollectionPagerAdapter = new DemoCollectionPagerAdapter( getSupportFragmentManager()); mViewPager = (ViewPager) findViewById(R.id.pager); mViewPager.setAdapter(mDemoCollectionPagerAdapter); } } // Since this is an object collection, use a FragmentStatePagerAdapter, // and NOT a FragmentPagerAdapter. public class DemoCollectionPagerAdapter extends FragmentStatePagerAdapter { public DemoCollectionPagerAdapter(FragmentManager fm) { super(fm); } @Override public Fragment getItem(int i) { Fragment fragment = new DemoObjectFragment(); Bundle args = new Bundle(); // Our object is just an integer :-P args.putInt(DemoObjectFragment.ARG_OBJECT, i + 1); fragment.setArguments(args); return fragment; } @Override public int getCount() { return 100; } @Override public CharSequence getPageTitle(int position) { return "OBJECT " + (position + 1); } } // Instances of this class are fragments representing a single // object in our collection. public static class DemoObjectFragment extends Fragment { public static final String ARG_OBJECT = "object"; @Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { // The last two arguments ensure LayoutParams are inflated // properly. View rootView = inflater.inflate( R.layout.fragment_collection_object, container, false); Bundle args = getArguments(); ((TextView) rootView.findViewById(android.R.id.text1)).setText( Integer.toString(args.getInt(ARG_OBJECT))); return rootView; } }
This example shows only the code necessary to create the swipe views. The following sections show how you can add tabs to help facilitate navigation between pages.
Add Tabs to the Action Bar
Action bar tabs offer users a familiar interface for navigating between and identifying sibling screens in your app.
To create tabs using ActionBar
, you need to enable
NAVIGATION_MODE_TABS
, then create several instances of
ActionBar.Tab
and supply an implementation of
the ActionBar.TabListener
interface for each one.
For example, in your activity's onCreate()
method, you can use code similar to this:
@Override public void onCreate(Bundle savedInstanceState) { final ActionBar actionBar = getActionBar(); ... // Specify that tabs should be displayed in the action bar. actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS); // Create a tab listener that is called when the user changes tabs. ActionBar.TabListener tabListener = new ActionBar.TabListener() { public void onTabSelected(ActionBar.Tab tab, FragmentTransaction ft) { // show the given tab } public void onTabUnselected(ActionBar.Tab tab, FragmentTransaction ft) { // hide the given tab } public void onTabReselected(ActionBar.Tab tab, FragmentTransaction ft) { // probably ignore this event } }; // Add 3 tabs, specifying the tab's text and TabListener for (int i = 0; i < 3; i++) { actionBar.addTab( actionBar.newTab() .setText("Tab " + (i + 1)) .setTabListener(tabListener)); } }
How you handle the ActionBar.TabListener
callbacks to change tabs
depends on how you've constructed your content. But if you're using fragments for each tab with
ViewPager
as shown above, the following
section shows how to switch between pages when the user selects a tab and also update the selected
tab when the user swipes between pages.
Change Tabs with Swipe Views
To switch between pages in a ViewPager
when the user selects
a tab, implement your ActionBar.TabListener
to select the appropriate page
by calling setCurrentItem()
on your
ViewPager
:
@Override public void onCreate(Bundle savedInstanceState) { ... // Create a tab listener that is called when the user changes tabs. ActionBar.TabListener tabListener = new ActionBar.TabListener() { public void onTabSelected(ActionBar.Tab tab, FragmentTransaction ft) { // When the tab is selected, switch to the // corresponding page in the ViewPager. mViewPager.setCurrentItem(tab.getPosition()); } ... }; }
Likewise, you should select the corresponding tab when the user swipes between pages with a
touch gesture. You can set up this behavior by implementing the
ViewPager.OnPageChangeListener
interface to change
the current tab each time the page changes. For example:
@Override public void onCreate(Bundle savedInstanceState) { ... mViewPager = (ViewPager) findViewById(R.id.pager); mViewPager.setOnPageChangeListener( new ViewPager.SimpleOnPageChangeListener() { @Override public void onPageSelected(int position) { // When swiping between pages, select the // corresponding tab. getActionBar().setSelectedNavigationItem(position); } }); ... }
Use a Title Strip Instead of Tabs
If you don't want to include action bar tabs and prefer to provide
scrollable tabs for a shorter
visual profile, you can use PagerTitleStrip
with
your swipe views.
Below is an example layout XML file for an
activity whose entire contents are a ViewPager
and a top-aligned
PagerTitleStrip
inside it. Individual pages (provided by the
adapter) occupy the remaining space inside the ViewPager
.
<android.support.v4.view.ViewPager xmlns:android="http://schemas.android.com/apk/res/android" android:id="@+id/pager" android:layout_width="match_parent" android:layout_height="match_parent"> <android.support.v4.view.PagerTitleStrip android:id="@+id/pager_title_strip" android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_gravity="top" android:background="#33b5e5" android:textColor="#fff" android:paddingTop="4dp" android:paddingBottom="4dp" /> </android.support.v4.view.ViewPager>