List grouped by various criteria

A guide to SortedList (part 4/5) — Section Lists

Index

1. Part 1 — Replacing ArrayList with SortedList
2. Part 2 — Deep dive into data operations
3. Part 3 — Separation of data and view concerns
4. Part 4 — Section Lists
5. Part 5 — Pagination
6. Bonus — Deep dive into data operations with JUnit4 tests.

In this part we will explore building section lists with SortedList. Continuing with our examples on Article, the UI we are going to build will group articles by their category, timestamp, author and content. There will also be an option to sort within a grouping.

In this case sorting is based on two things. A top level sorting for grouping and another sorting within a group.

To encapsulate grouping of an article and its related behaviour, lets create a class GroupedArticle.java

A GroupedArticle represents an article and a grouping. There are four types of groupings, with each having its own creator method. Each creator method byTimestamp byCategory byContent and byAuthor creates a pair of GroupedArticle instances, representing an article and a grouping.

Each of this creator methods generate a grouping and a group key for an article. A group key is an integer index which represents the position of a group within its type. So when groups are compared they are compared by their group key. When we compare two articles with in a group, we compare it with an ArticleComparator

Create a dataset named GroupedArticleDataset.java

Lets create GroupedArticleViewHolder.java to abstract header and articles views in recycler views.

Lets build header view. Create xml item_header.xml

And a corresponding HeaderViewHolder.java

Create item_grid_section_article.xml that will represent a layout for article.

Corresponding ArticleViewHolder.java

Lets create an adapter named SectionsAdapter.java

Wire the adapter to a recycler view in an activity. Create activity_section_list.xml

Create a SectionListActivity.java and wire up the adapter.

Run this activity, play around with group by & sort by options. You should be noticing similar behaviour as presented in the illustration at the beginning of the article.

Every list is sorted in some way or another, therefore SortedList becomes the default choice for backing the data. The only tough problem is to model and map sorting behaviour to SortedList. Through this post and previous posts, we have learned many techniques to solving it.

In the next post we will learn to use SortedList in a list UI that supports paging.

You can the find all the code on GitHub

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