Endless/infinite RecyclerView with smooth scroll and fling...
Most open source endless ListView or RecyclerView implementations in Android have poor UX; a scroll or fling action
will stop when the list reaches its current capacity, the more data is loaded - some more sophisticated
implementations might then "peek" the new content, but as often as not it's simply loaded up off screen without
alerting the user.
A correctly configured EndlessRecyclerView will behave as if the content were truly endless, and allow scrolling
or flinging as far as the developer instructs.
Specify a threshold, in pixels. This is an arbitrary value and can be dynamic - e.g., you could set the threshold
to three times the height of the RecyclerView, updating the value in onLayout. Once a threshold is set,
any scroll operation will measure the existing content against the current scroll and dimension of the recycler view -
if there is not enough content to meet or exceed the threshold value off screen (generally, below), then a callback
is fired with the number of items (generally rows) needed to consume that space entirely: space to fill / average size of an item (row). How that callback is handled is up to you - since RecyclerViews and Adapters are
generally very custom implementations, we just provide a callback on the adapter - the fill method, which is
passed a single parameter: the quantity of items the widget thinks is needed to create enough content to reach
the defined threshold.
If your RecyclerView is displaying data from a remote server, you can us the technique shown in the demo -
immediately fill the adapter's data set with placeholder values (e.g., nulls, or maybe data items with an
"uninitialized" flag), notify the adapter, then send a network request to replace those placeholders when data becomes
available (and notify again).
If your RecyclerView is displaying local data, or data sets that can be constructed immediately, then that second
step is unnecessary.
EndlessRecyclerView is available on jcenter. Make sure jcenter is in your module's build.gradle repositories
(default for Android Studio). Then add the following line to your dependencies:
compile 'com.qozix:endlessrecyclerview:1.0'
Use EndlessRecyclerView in place of a normal RecyclerView. Set your threshold using
setVerticalThreshold(int threshold) for vertical layouts, or the horizontal version for horizontal layouts.
For your Adapter, subclass EndlessAdapter just as you would a standard RecyclerView.Adapter, but with one additional
method defined: fill(int quantity). This method should handle adding items to your dataset when the user scrolls near
the bounds defined by your threshold.
JavaDocs are included in the repo, under the top-level docs directory.
There is a demo module included in the repo. The SimpleDemoActivity uses a very straightforward implementation,
while the MockNetworkDemoActivity uses some of the more advanced techniques described above.