How can we temporarily store an object in Android?

Temporarily saving an object in Android can be done in several ways, depending on its lifespan and the need for access after the component is finished:

• View State: Objects related to a View can be saved in its state, which is restored when the View is recreated (for example, during screen rotation). onSaveInstanceState() and onRestoreInstanceState() are used.
• ViewModel: The best way to save data related to UI that should survive configuration changes of Activity/Fragment (for example, screen rotations). ViewModel exists until the ViewModelStoreOwner is destroyed.

  // In Activity/Fragment
  val viewModel = ViewModelProvider(this).get(MyViewModel::class.java)
  
  // In ViewModel
  class MyViewModel : ViewModel() {
      var myObject: MyData? = null
  }
  

• onRetainCustomNonConfigurationInstance() (deprecated): A method in Activity to save arbitrary objects that will survive configuration changes. getLastNonConfigurationInstance() is used to retrieve the object. Deprecated in favor of ViewModel.

  // In Activity
  override fun onRetainCustomNonConfigurationInstance(): Any? {
      return myObjectToRetain
  }
  
  // To get the object
  val retainedObject = lastCustomNonConfigurationInstance as? MyData
  

• Application class: For objects that should live throughout the entire application lifecycle. Use with caution to avoid storing too much data.
• Temporary files: For larger objects that do not fit directly into memory or require short-term storage on disk.

Method	Lifespan	Usage
View State	View life + recreation state	Small data related to View
ViewModel	Activity/Fragment life	UI data surviving configuration changes
onRetainCustomNonConfigurationInstance()	Activity life + recreation state	Arbitrary objects (deprecated)
Application class	Application life	Global objects
Temporary files	Developer-defined	Large objects, temporary storage