Android handler: Can't create handler inside thread that has not called Looper.prepare()

Question

I have a thread:

public class KelvinThread implements Runnable {

private Handler mSoundHandler;

public KelvinThread() {
    super();
    mSoundHandler = new Handler();
}

private Runnable mSoundThread = new Runnable() {
    public void run() {
        // my treatment
    }
};

@Override
public void run() {
    while (true) {
        // ....
        mSoundHandler.postDelayed(mSoundThread, 2000);
        // ....
    }
}

This thread "KelvinThread" is created and started from another Thread.

I have this error:

Can't create handler inside thread that has not called Looper.prepare()

when my handler is allocated : mSoundHandler = new Handler();

Thank you for your help guys !

In seven hells why you are mixing Handler with native Thread? I think this is very ungly solution and you shouldn't do it - it seems like bad application logic design. — Simon Dorociak
It is not really. Sometimes you have to do it, for example to trigger UI changes from thread or may other cases. Really depends. — Volodymyr Lykhonis
Hi Ragnar, I read your advice. But how can I do a trigger without Handler ? Is there another way to do that ? — anthony

Volodymyr Lykhonis Volodymyr Lykhonis · Accepted Answer · 2014-04-17T18:43:49

Please refer to Looper documentation. There is also example.

UPD You might also be able to use Looper.getMainLooper() to attach handler to main looper instead of creating thread one.

Android handler: Can't create handler inside thread that has not called Looper.prepare()

1 Answers