page.title=Creating a 2D Picker @jd:body

This lesson teaches you to

  1. Add a Page Grid
  2. Implement a Page Adapter

Related Samples

You should also read

The 2D Picker pattern in Android Wear allows users to navigate and choose from a set of items shown as pages. The Wearable UI Library lets you easily implement this pattern using a page grid, which is a layout manager that allows users to scroll vertically and horizontally through pages of data.

To implement this pattern, you add a GridViewPager element to the layout of your activity and implement an adapter that provides a set of pages by extending the FragmentGridPagerAdapter class.

Add a Page Grid

Add a GridViewPager element to your layout definition as follows:

<android.support.wearable.view.GridViewPager
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/pager"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

You can use any of the techniques described in Defining Layouts to ensure that your 2D picker works on both round and square devices.

Implement a Page Adapter

A page adapter provides a set of pages to populate a GridViewPager component. To implement this adapter, you extend the FragmentGridPagerAdapter class from the Wearable UI Library

The following snippet shows how to provide a set of static cards with custom background images:

public class SampleGridPagerAdapter extends FragmentGridPagerAdapter {

    private final Context mContext;
    private List mRows;

    public SampleGridPagerAdapter(Context ctx, FragmentManager fm) {
        super(fm);
        mContext = ctx;
    }

    static final int[] BG_IMAGES = new int[] {
        R.drawable.debug_background_1, ...
        R.drawable.debug_background_5
    };

    // A simple container for static data in each page
    private static class Page {
        // static resources
        int titleRes;
        int textRes;
        int iconRes;
        ...
    }

    // Create a static set of pages in a 2D array
    private final Page[][] PAGES = { ... };

    // Override methods in FragmentGridPagerAdapter
    ...
}

The adapter calls getFragment() and getBackgroundForRow() to retrieve the content to display for each row:

// Obtain the UI fragment at the specified position
@Override
public Fragment getFragment(int row, int col) {
    Page page = PAGES[row][col];
    String title =
        page.titleRes != 0 ? mContext.getString(page.titleRes) : null;
    String text =
        page.textRes != 0 ? mContext.getString(page.textRes) : null;
    CardFragment fragment = CardFragment.create(title, text, page.iconRes);

    // Advanced settings (card gravity, card expansion/scrolling)
    fragment.setCardGravity(page.cardGravity);
    fragment.setExpansionEnabled(page.expansionEnabled);
    fragment.setExpansionDirection(page.expansionDirection);
    fragment.setExpansionFactor(page.expansionFactor);
    return fragment;
}

// Obtain the background image for the row
@Override
public Drawable getBackgroundForRow(int row) {
    return mContext.getResources().getDrawable(
            (BG_IMAGES[row % BG_IMAGES.length]), null);
}

The following example shows how to retrieve the background to display for a specific page in the grid: 

// Obtain the background image for the specific page
@Override
public Drawable getBackgroundForPage(int row, int column) {
    if( row == 2 && column == 1) {
        // Place image at specified position
        return mContext.getResources().getDrawable(R.drawable.bugdroid_large, null);
    } else {
        // Default to background image for row
        return GridPagerAdapter.BACKGROUND_NONE;
    }
}

The getRowCount() method tells the adapter how many rows of content are available, and the getColumnCount() method tells the adapter how many columns of content are available for each of the rows.

// Obtain the number of pages (vertical)
@Override
public int getRowCount() {
    return PAGES.length;
}

// Obtain the number of pages (horizontal)
@Override
public int getColumnCount(int rowNum) {
    return PAGES[rowNum].length;
}

The adapter implementation details depend on your particular set of pages. Each page provided by the adapter is of type Fragment. In this example, each page is a CardFragment instance that uses one of the default card layouts. However, you can combine different types of pages in the same 2D picker, such as cards, action icons, and custom layouts depending on your use cases.

Figure 1: The GridViewPager sample.

Not all rows need to have the same number of pages. Notice that in this example the number of colums is different for each row. You can also use a GridViewPager component to implement a 1D picker with only one row or only one column.

The GridViewPager class provides support for scrolling in cards whose content does not fit the device screen. This example configures each card to expand as required, so users can scroll through the card's content. When users reach the end of a scrollable card, a swipe in the same direction shows the next page on the grid, if one is available.

You can specify a custom background for each page with the getBackgroundForPage() method. When users swipe to navigate across pages, the GridViewPager class applies parallax and crossfade effects between different backgrounds automatically.

Assign an adapter instance to the page grid

In your activity, assign an instance of your adapter implementation to the GridViewPager component:

public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        ...
        final GridViewPager pager = (GridViewPager) findViewById(R.id.pager);
        pager.setAdapter(new SampleGridPagerAdapter(this, getFragmentManager()));
    }
}