How to use Handler and handleMessage in Kotlin?

handler in android example
handler postdelayed in kotlin
android handler message example
android-handler postdelayed
handler in java
kotlin run on ui thread
handler sendemptymessage
handler removecallbacks

Java code:

private final Handler mHandler = new Handler() {
    @Override
    public void handleMessage(Message msg) {
       // code here
    }
};

How to convert this java code to Kotlin?

I tried this:

private val mHandler = object : Handler() {
    fun handleMessage(msg: Message) {
       // code here
    }
}

But this is seems to be incorrect and gives a compile time error on object

Problem: The syntax to override handleMessage() method of the Handler class is incorrect.

Solution: Add override keyword before the function that you want to override.

private val mHandler = object : Handler() {

    override fun handleMessage(msg: Message?) {
        // Your logic code here.
    }
}

Update: As @BeniBela's comment, when using above code, a lint warning will be displayed

This Handler class should be static or leaks might occur.

Since this Handler is declared as an inner class, it may prevent the outer class from being garbage collected. If the Handler is using a Looper or MessageQueue for a thread other than the main thread, then there is no issue.

If the Handler is using the Looper or MessageQueue of the main thread, you need to fix your Handler declaration, as follows: Declare the Handler as a static class; In the outer class, instantiate a WeakReference to the outer class and pass this object to your Handler when you instantiate the Handler; Make all references to members of the outer class using the WeakReference object.

class OuterClass {

    // In the outer class, instantiate a WeakReference to the outer class.
    private val outerClass = WeakReference<OuterClass>(this)

    // Pass the WeakReference object to the outer class to your Handler
    // when you instantiate the Handler
    private val mMyHandler = MyHandler(outerClass)

    private var outerVariable: String = "OuterClass"

    private fun outerMethod() {

    }

    // Declare the Handler as a static class.
    class MyHandler(private val outerClass: WeakReference<OuterClass>) : Handler() {

        override fun handleMessage(msg: Message?) {
            // Your logic code here.
            // ...

            // Make all references to members of the outer class 
            // using the WeakReference object.
            outerClass.get()?.outerVariable
            outerClass.get()?.outerMethod()
        }
    }
}

Communicate with the UI thread, As a quick example of how to use a Thread with a basic Handler in an Handler( ) { @Override public void handleMessage(Message msg)� Let’s Build an Android Handler example in kotlin: In Android app development using kotlin language. In the example on Click button thread will run and update the UI counter and progress bar using Handler. You can see the counting in TextView label . Let’s see the steps to how to do it. Step 1.

You may do it a bit easier (without WeakReference) by passing looper to handler:

val handler = object:  Handler(Looper.getMainLooper()) {
        override fun handleMessage(msg: Message) {
            doStuff()
        }
    }

Handler, You use Handler to order threads to perform the desired action. Any thread can be used public void handleMessage(Message msg) { super. I was learning about Looper and Handler and most time I read about it that it use to Communicate with UI thread. But then I saw the code which was child class of Handler with handleMessage(msg : Message) method then I got confused, because we can interact with GUI thread without extending Handler class. As example in kotlin android. val handler

In my case :

@SuppressLint("HandlerLeak")
    private inner class MessageHandler(private val mContext: Context) : Handler() {
        override fun handleMessage(msg: Message) {
            when (msg.what) {

            }
        }
    }

Android: How to send a message from a Thread to a Handler , Making adept use of threads on Android can help you boost your app's by the handler's handleMessage(Message) method (requiring you to� In Android Studio, right-click on the com.raywenderlich.mcwenderlich root package folder and select New ▸ Kotlin File/Class. Next, name it OrderHandlerThread and select Class for Kind. Make it extend HandlerThread. The constructor of HandlerThread requires a String as parameter.

Mastering Android Handler. What is Handler, internals and Best , You will learn how to use HandlerThread to receive messages from a Runnable root package folder and select New ▸ Kotlin File/Class. //1 return object: Handler(looper) { //2 override fun handleMessage(msg: Message?) I'm a newbie to Kotlin. I'm trying to convert my old java code into Kotlin. When I try to create a new Handler and override handleMessage() method I got an answer at: How to use Handler and handleM

Multi-Threaded Android: Handler, Thread, Looper, and Message , You can think of a Handler as an advanced mechanism to handle a queue, Android (22); Courses (2); Digests (11); Game dev (6); Games (5); General (17); Kotlin (1); My projects (7) A good example of using a Handler is when you have a Runnable, you public void handleMessage(Message msg) {. A Handler object receives messages and runs code to handle the messages. Normally, you create a Handler for a new thread, but you can also create a Handler that's connected to an existing thread. When you connect a Handler to your UI thread, the code that handles messages runs on the UI thread.

Threading With HandlerThread in Android, Preparing the Looper To use the Looper class, we must first call the prepare() class LooperHandler : Handler() { override fun handleMessage(message:� If you want to use a handler The sendMessage versions allow you to enqueue a Message object containing a bundle of data that will be processed by the handler’s handleMessage Kotlin; 325

Comments
  • This gives a HandlerLeak lint warning
  • @BeniBela thanks for your info, please check my updated answer.