Extending the BlogPost example with BindingAdapter

First, to add a header row, I need a way for the ListView’s adapter to distinguish a detail row from a header row. The header row only has static data defined in its XML layout; the adapter only needs to inflate the layout for a header row, whereas for a detail row, the adapter also needs to apply the model data to the row.Here is the header layout xml:

So in our list of blog post rows, we really just need a dummy placeholder entry for the header. I accomplish this by introducing a new interface:

public interface BlogPostRow {}

Then I make the BlogPost class implement BlogPostRow:

public class BlogPost implements BlogPostRow {
  public DateTime date;
  public String title;
  public String content;

  public BlogPost(String title, String content, DateTime date) {
    this.title = title;
    this.content = content;
    this.date = date;
  }
}

Finally in the activity class, I add a static function to prepend the list of rows returned by our BlogPostService with a single dummy row for the header:

public class ListBlogsActivity extends Activity {

  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    final BlogListAdapter blogListAdapter = new BlogListAdapter(this, prependHeader(new ArrayList()));
    ListView blogPostListView = (ListView) findViewById(R.id.blogposts);

    blogPostListView.setAdapter(blogListAdapter);

    getLoaderManager().initLoader(0, savedInstanceState,
        new LoaderManager.LoaderCallbacks<List>() {
          @Override public Loader<List> onCreateLoader(int id, Bundle args) {
            return new BlogPostLoader(ListBlogsActivity.this);
          }

          @Override public void onLoadFinished(Loader<List> loader, List data) {

            blogListAdapter.setData(prependHeader(data));
          }

          @Override public void onLoaderReset(Loader<List> loader) {
            blogListAdapter.setData(prependHeader(new ArrayList()));
          }
        }
    ).forceLoad();
  }

  private static List prependHeader(List blogPosts) {
    List blogPostRows = new ArrayList();
    blogPostRows.add(new BlogPostRow() {});
    blogPostRows.addAll(blogPosts);
    return blogPostRows;
  }
}

Now my adapter has a way of distinguishing header vs detail rows: a detail row is an instance of BlogPost, and a header row is not.

Finally, the adapter:

public class BlogListAdapter exte
public class BlogListAdapter extends BindingAdapter<BlogPostRow, BlogListAdapter.DetailViewHolder> {
  private static final DateTimeFormatter dtf = DateTimeFormat.forPattern("MM/dd");
  private static final int MAX_SUMMARY_LEN = 100;
  private List blogPostRows = new ArrayList();

  public BlogListAdapter(Context context, List blogPostRows) {
    super(context);
    this.blogPostRows = blogPostRows;
  }

  public void setData(List data) {
    if (blogPostRows != null) {
      blogPostRows.clear();
    } else {
      blogPostRows = new ArrayList();
    }
    if (data != null) {
      blogPostRows.addAll(data);
    }
    notifyDataSetChanged();
  }

  @Override public View newView(LayoutInflater inflater, int position, ViewGroup container) {
    return (getItem(position) instanceof BlogPost) ?
        inflater.inflate(R.layout.blogpostdetail, null) : inflater.inflate(R.layout.blogpostheader, null);
  }

  @Override public DetailViewHolder buildViewHolder(View view, int position) {
    return (getItem(position) instanceof BlogPost) ? new DetailViewHolder(view) : null;
  }

  @Override public void bindView(BlogPostRow item, int position, View view, DetailViewHolder vh) {
    if (item instanceof BlogPost) {
      BlogPost post = (BlogPost) item;
      vh.blogDate.setText(dtf.print(post.date));

      vh.blogTitle.setText(post.title);

      String summary = post.content.substring(0, Math.min(MAX_SUMMARY_LEN, post.content.length()));
      vh.blogSummary.setText(summary);
    }
  }

  @Override public int getItemViewType(int position) {
    return (getItem(position) instanceof BlogPost) ? ViewType.DETAIL_ITEM.ordinal() : ViewType.HEADER_ITEM.ordinal();
  }

  @Override public int getViewTypeCount() {
    return ViewType.values().length;
  }

  @Override
  public int getCount() {
    return blogPostRows.size();
  }

  @Override
  public BlogPostRow getItem(int i) {
    return blogPostRows.get(i);
  }

  @Override
  public long getItemId(int i) {
    return i;
  }

  public enum ViewType {
    DETAIL_ITEM, HEADER_ITEM
  }

  static class DetailViewHolder {
    TextView blogDate;
    TextView blogTitle;
    TextView blogSummary;

    DetailViewHolder(View view) {
      blogDate = (TextView) view.findViewById(R.id.blogdate);
      blogTitle = (TextView) view.findViewById(R.id.blogtitle);
      blogSummary = (TextView) view.findViewById(R.id.blogsummary);
    }
  }
}

Enabling a Header Row

• The ViewType enum, which defines the types of views a row can be
• getViewTypeCount(), which provides the number of possible view types for a row
• getItemViewType(), which defines what type of view a particular row is