What is HandlerThread and when to use it?

Answer

What is HandlerThread?

HandlerThread is a Thread subclass that has its own Looper built-in, making it easy to handle messages and runnables sequentially on a background thread.

Why Use HandlerThread?

Unlike a regular Thread (which executes once and dies), HandlerThread:

• Stays alive and processes tasks in a queue
• Guarantees sequential execution of tasks
• Provides a Looper that you can attach Handlers to
• Avoids creating new threads repeatedly

Code Example

Copy code// Create and start HandlerThread
val handlerThread = HandlerThread("MyBackgroundThread")
handlerThread.start()

// Create Handler attached to HandlerThread's Looper
val backgroundHandler = Handler(handlerThread.looper)

// Post tasks to run on background thread
backgroundHandler.post {
    // This runs on HandlerThread, not UI thread
    val data = fetchDataFromNetwork()
    
    // Switch to UI thread to update UI
    mainHandler.post {
        updateUI(data)
    }
}

// Don't forget to quit when done
handlerThread.quitSafely()

When to Use HandlerThread

HandlerThread vs Other Options

Important Points

• Always call quit() or quitSafely() when done
• quitSafely() processes pending messages before terminating
• The Looper is only available after start() is called