It's not an easy task to write a performant Android app that load large images or process a large number of small images. These operations tend to wreak havoc on your app's memory management.
Glide
Android Developer site has a series of advice on how to handle such a scenario, and one of their recommendations is to use the Glide library.
Glide is a fast and efficient image loading library for Android focused on smooth scrolling. Glide offers an easy to use API, a performant and extensible resource decoding pipeline and automatic resource pooling.
...
Glide’s primary focus is on making scrolling any kind of a list of images as smooth and fast as possible, but Glide is also effective for almost any case where you need to fetch, resize, and display a remote image.
Glide is doing all the heavy-lifting work in the background, so images will be load fast & efficiently.
RecyclerView
RecyclerView is a widget that allows you to create lists of items for large dataset. It's much more advanced and flexible than ListView.
One of the important things that RecyclerView can do is UI virtualization.
Example
The device screen can only show 10 items on the screen, and you have 1000 items in the dataset. RecyclerView will probably generate the following:
| Element Count | Viewport | Note |
|---|---|---|
| n/2 | Not visible | Buffer if the user scrolls up |
| n | Visible | On screen |
| n/2 | Not visible | Buffer if user scroll down |
RecyclerView will only create a total of 20 UI elements (5 + 10 + 5), instead of 1000 in one go. As the user scroll along, it will recycle the created UI element and bind it with new data.
Empty spaces when fast flick through the image gallery
If the image to be loaded is a 'new' image (not previously loaded), Glide will have to load the bitmap and cache it (to the memory and/or disk). Inflating images will take a longer time because it's operationally expensive and memory intensive, in comparison with other UI elements.
And that is why if you have implemented an image gallery using RecyclerView & Glide, and the user decided to flick through the list extremely fast, and the app will typically show a large amount of white space.
Solution
Use the RecyclerView integration library.
The RecyclerView integration library makes the RecyclerViewPreloader available in your application. RecyclerViewPreloader can automatically load images just ahead of where a user is scrolling in a RecyclerView.
Combined with the right image size and an effective disk cache strategy, this library can dramatically decrease the number of loading tiles/indicators users see when scrolling through lists of images by ensuring that the images the user is about to reach are already in memory.
Using the library in Xamarin.Android project
I've ported over the library to a nuget package, so you can use it in your Xamarin.Android project.
If you have any question, you can hop over to the project's repository.