What is the difference between Application context and Activity context?

The Application context provides access to application-wide resources, with a lifespan of the entire application. The Activity context is tied to the lifecycle of a specific Activity, contains information about a particular screen, and provides access to resources specific to that Activity (e.g., theme).

Main differences:

• Lifespan: The Application context lives as long as the application runs, while the Activity context only exists while the corresponding Activity is active.
• Scope: The Application context is global for the entire application, whereas the Activity context is local to a specific screen.
• Access to resources: The Application context is used for common resources, while the Activity context is used for resources specific to that Activity (e.g., theme).
• Memory leaks: Incorrect use of the Activity context (e.g., storing it in a static field) can lead to memory leaks because it references the Activity and its resources. The Application context is safer for long-term storage.

Examples of usage:

• Accessing common strings or colors:

  // Anywhere in the application
  val appName = applicationContext.getString(R.string.app_name)
  

• Creating a View in an Activity:

  // Inside an Activity
  val textView = TextView(this /* or this@MyActivity */)
  

• Starting a new Activity:

  // Inside an Activity
  val intent = Intent(this, AnotherActivity::class.java)
  startActivity(intent)
  

• Accessing SharedPreferences:

  // Both contexts work, but when using Context.MODE_PRIVATE, Activity context is preferred
  val prefs = getSharedPreferences("my_prefs", Context.MODE_PRIVATE)
  

It is important to use the appropriate context to prevent memory leaks and ensure correct app behavior. In most cases, the Activity context is used for UI-specific operations, while the Application context is used for tasks not tied to a specific screen.