Result Paging in Chat Client SDKs

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Twilio's Programmable Chat client SDKs use paging to improve performance when accessing potentially large collections of chat objects.

Paginators

Public Channels, User Channels, and the Members list for each channel are exposed through Paginators. In JavaScript, Messages are also paged using Paginators. When requesting an initial set of any of these entities, your provided callback mechanism will receive a result indicating the success or failure of the operation as well as a paginator to access the items.

While the signature of the individual methods will vary by SDK platform, each paginator has the following accessors:

A way to obtain the items.
A Boolean property indicating if there are subsequent pages.
A method taking the same callback mechanism as the original call to request the next page.

Result Paging: Obtain a List of Public Channel Descriptors

1// Get messages from the newest to oldest
2channel
3  .getMessages(20 /* by pages of 20 messages */)
4  .then(function(messagesPage) {
5    messagesPage.items.forEach(function(message) {
6      // do stuff for each message
7    });
8    // note, that by default pages are in "backwards" order,
9    // so you should ask for previous page, not the next one
10    if (messagesPage.hasPrevPage) {
11      return messagesPage.prevPage(); // here we can ask for following page
12    }
13  });
14
15// Get messages from the message with id 3 to newest
16channel.getMessages(20, 3, 'forward').then(function(messagesPage) {
17  /* handle page the same way as above */
18});
19
20// Handle multiple pages
21// Unfortunately, js has no asynchronous iterators yet, so there should be
22// some boilerplate here. One of the way to go through all messages would be
23// like this:
24function processPage(page) {
25  page.items.forEach(function(message) {
26    /* do something for message */
27  });
28  if (page.hasNextPage) {
29    page.nextPage().then(processPage);
30  } else {
31    // all messages read!
32  }
33}
34channel.getMessage(10, null, 'forward').then(processPage);

Messages (Android, iOS)

The messages collection behaves a bit differently than channels and members since there is a temporal quality to how the objects are typically presented.

The messages collection objects offer the following ways to access items:

getLastMessages fetches the specified number of messages, starting with the most recent in the collection.
getMessagesBefore fetches messages before (and including) the anchor message index specified.
getMessagesAfter fetches messages after (and including) the anchor message index specified.
messageWithConsumptionIndex fetches the message with the specified index or, if that message is no longer available, the message directly before it.
messageWithIndex fetches the message specified by the index, if available.

Result Paging: Messages

1// Fetch the initial messages
2messagesObject.getLastMessages(BATCH_SIZE, new CallbackListener<List<Message>>()
3{
4  @Override
5  public void onSuccess(List<Message> messagesArray) {
6    // Display initial messages in your UI
7  }
8});
9
10// ... user scrolls through messages list
11
12// Fetch next set of messages when you get close to the
13// end of your local messages
14messagesObject.getMessagesBefore(firstMessage.getMessageIndex(), BATCH_SIZE,
15                                 new CallbackListener<List<Message>>()
16{
17  @Override
18  public void onSuccess(List<Message> messagesArray) {
19    // Display latest messages in your UI
20  }
21});

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