Why is it important to return to the main user interface thread to display a Toast message?

In Android, all operations related to updating the user interface must be performed on the main (UI) thread. Toast is a UI element, and its display requires interaction with the UI thread. If you try to show a Toast from a background thread, the application may throw an error or the Toast simply may not appear.

Main reasons:

• The UI thread is responsible for rendering and handling interface events.
• Thread safety: UI elements are not thread-safe.
• Ensuring proper synchronization and preventing crashes.

Example in Kotlin:

runOnUiThread {
    Toast.makeText(context, "Message", Toast.LENGTH_SHORT).show()
}