How does facebook or instagram app retain images or data after entering the app with no internet connection?

Question

In Facebook app, for example, I login with my internet connection. Then I close the app, turn off the internet and close all my system tabs. Then even though my internet connection is off, I see the images and data that had been previously loaded still retained.

How does Facebook app do that? What should I do if wanted to implement such a feature in my Android app?

Answer 1

i use 'Picasso' Library for caching, loading... images from internet :

http://square.github.io/picasso/

Automatic memory and disk caching

Picasso.with(context)
   .load(url)
   .resize(50, 50)
   .centerCrop()
   .into(imageView)

for data, you can store data using shared preferences for small stuff or a local database like sqlite