onTrimMemory(): Called when the operating system has determined that it is a good time for a process to trim unneeded memory from its process. This will happen for example when it goes in the background and there is not enough memory to keep as many background processes running as desired.

Android can reclaim memory for from your app in several ways or kill your app entirely if necessary to free up memory for critical tasks. To help balance the system memory and avoid the system's need to kill your app process, you can implement the ComponentCallbacks2 interface in your Activity classes. The provided onTrimMemory() callback method allows your app to listen for memory related events when your app is in either the foreground or the background, and then release objects in response to app lifecycle or system events that indicate the system needs to reclaim memory.