如何在网格寻呼机适配器中循环显示3个卡片段？

Question

我正在尝试遍历网格寻呼机适配器中的3个卡片段。我的网格寻呼机适配器代码在这里：

/**
 * Constructs fragments as requested by the GridViewPager. For each row a different background is
 * provided.
 * <p>
 * Always avoid loading resources from the main thread. In this sample,the background images are
 * loaded from an background task and then updated using {@link #notifyRowBackgroundChanged(int)}
 * and {@link #notifyPageBackgroundChanged(int, int)}.
 */
public class SampleGridPagerAdapter extends FragmentGridPagerAdapter {
private static final int TRANSITION_DURATION_MILLIS = 100;

private final Context mContext;
private List<Row> mRows;
private ColorDrawable mDefaultBg;

private ColorDrawable mClearBg;

@SuppressLint("ResourceAsColor")
public SampleGridPagerAdapter(Context ctx, FragmentManager fm) {
    super(fm);
    mContext = ctx;

    mRows = new ArrayList<Row>();

    mRows.add(new Row(cardFragment(R.string.welcome_title, R.string.welcome_text),
            cardFragment(R.string.about_title, R.string.about_text),
            cardFragment(R.string.cards_title, R.string.cards_text),
            cardFragment(R.string.expansion_title, R.string.expansion_text)));

    mDefaultBg = new ColorDrawable(R.color.dark_grey);
    mClearBg = new ColorDrawable(android.R.color.transparent);
}

LruCache<Integer, Drawable> mRowBackgrounds = new LruCache<Integer, Drawable>(3) {
    @Override
    protected Drawable create(final Integer row) {
        int resid = BG_IMAGES[row % BG_IMAGES.length];
        new DrawableLoadingTask(mContext) {
            @Override
            protected void onPostExecute(Drawable result) {
                TransitionDrawable background = new TransitionDrawable(new Drawable[] {
                        mDefaultBg,
                        result
                });
                mRowBackgrounds.put(row, background);
                notifyRowBackgroundChanged(row);
                background.startTransition(TRANSITION_DURATION_MILLIS);
            }
        }.execute(resid);
        return mDefaultBg;
    }
};

LruCache<Point, Drawable> mPageBackgrounds = new LruCache<Point, Drawable>(3) {
    @Override
    protected Drawable create(final Point page) {
        // place bugdroid as the background at row 2, column 1
        if (page.y == 2 && page.x == 1) {
            int resid = R.drawable.bugdroid_large;
            new DrawableLoadingTask(mContext) {
                @Override
                protected void onPostExecute(Drawable result) {
                    TransitionDrawable background = new TransitionDrawable(new Drawable[] {
                            mClearBg,
                            result
                    });
                    mPageBackgrounds.put(page, background);
                    notifyPageBackgroundChanged(page.y, page.x);
                    background.startTransition(TRANSITION_DURATION_MILLIS);
                }
            }.execute(resid);
        }
        return GridPagerAdapter.BACKGROUND_NONE;
    }
};

private Fragment cardFragment(int titleRes, int textRes) {
    Resources res = mContext.getResources();
    CardFragment fragment =
            CardFragment.create(res.getText(titleRes), res.getText(textRes));
    // Add some extra bottom margin to leave room for the page indicator
    fragment.setCardMarginBottom(
            res.getDimensionPixelSize(R.dimen.card_margin_bottom));
    return fragment;
}

static final int[] BG_IMAGES = new int[] {
        R.drawable.debug_background_1,
        R.drawable.debug_background_2,
        R.drawable.debug_background_3,
        R.drawable.debug_background_4,
        R.drawable.debug_background_5
};

/** A convenient container for a row of fragments. */
private class Row {
    final List<Fragment> columns = new ArrayList<Fragment>();

    public Row(Fragment... fragments) {
        for (Fragment f : fragments) {
            add(f);
        }
    }

    public void add(Fragment f) {
        columns.add(f);
    }

    Fragment getColumn(int i) {
        return columns.get(i);
    }

    public int getColumnCount() {
        return columns.size();
    }
}

@Override
public Fragment getFragment(int row, int col) {
    Row adapterRow = mRows.get(row);
    return adapterRow.getColumn(col);
}

@Override
public Drawable getBackgroundForRow(final int row) {
    return mRowBackgrounds.get(row);
}

@Override
public Drawable getBackgroundForPage(final int row, final int column) {
    return mPageBackgrounds.get(new Point(column, row));
}

@Override
public int getRowCount() {
    return mRows.size();
}

@Override
public int getColumnCount(int rowNum) {
    return mRows.get(rowNum).getColumnCount();
}

class DrawableLoadingTask extends AsyncTask<Integer, Void, Drawable> {
    private static final String TAG = "Loader";
    private Context context;

    DrawableLoadingTask(Context context) {
        this.context = context;
    }

    @Override
    protected Drawable doInBackground(Integer... params) {
        Log.d(TAG, "Loading asset 0x" + Integer.toHexString(params[0]));
        return context.getResources().getDrawable(params[0]);
    }
}
}

我从这里找到的google开发人员示例代码开始：https://developer.android.com/samples/GridViewPager/project.html并将其修改为一行卡片段。有没有办法反复循环它们？