java.lang.RuntimeException: Only one Looper may be created per thread

Question

I have a simple thread that goes like this:

public class AwesomeRunnable extends Thread {

    Handler thisHandler = null;
    Handler uihandler = null;
    String update = null;
    long time = 0;

    public AwesomeRunnable(Handler h, long howLong) {
        uihandler = h;
        time = howLong;
    }

    public void run() {
        Looper.prepare();
        thisHandler = new Handler();
  ...

EDIT: ADDED CODE THAT STARTS THE RUNNABLE

public class StartCycle implements Runnable {

    @Override
    public void run() {

        pomodoroLeft = numPomodoro;
        while(pomodoroLeft > 0) {
            pomodoroLeft--;
            actualSeconds = 6 * ONE_SECOND;
            runnable = new AwesomeRunnable(myHandler, actualSeconds);
            runnable.start();
            waitForClock();

It is an inner class of a main activity. This thread, however runs not on the main activity, but inside of another thread that runs on the main activity.

Anyway, this example is exactly the same as here, but for some reason it gives me java.lang.RuntimeException: Only one Looper may be created per thread.

I did not create any other loopers, at least explicitly anywhere.

That looks fine. Which line is throwing the exception? Which thread? (If you're looking at the logcat output in a terminal window, use `adb logcat -v threadtime` to show the thread ID on each line.) Something must be creating a looper twice in a single thread, so you need to figure out if it's running in the wrong thread, or something running twice in the new thread. — fadden, Apr 13 '14 at 03:47
@fadden `Looper.prepare();` is throwing the exception. Ok...will try to go through log output as you suggested. — user3081519, Apr 13 '14 at 03:51
@fadden Actually the first line of the error message is: FATAL EXCEPTION: main. Does it mean it somehow creates another looper on the main thread? But why? — user3081519, Apr 13 '14 at 03:58
Sounds like it's trying to. If the two numbers (pid and tid) are the same, then it's definitely trying to create a new Looper in the main thread. Check the stack trace and see what's calling the function. — fadden, Apr 13 '14 at 05:01

score 97 · Accepted Answer · edited Nov 09 '15 at 21:44

97

java.lang.RuntimeException: Only one Looper may be created per thread

The exception is thrown because you (or core Android code) has already called Looper.prepare() for the current executing thread.

The following checks whether a Looper already exists for the current thread, if not, it creates one, thereby avoiding the RuntimeException.

    public void run() 
    {
            if (Looper.myLooper() == null)
            {
              Looper.prepare();
            }
            thisHandler = new Handler();

         ....
    }

edited Nov 09 '15 at 21:44

Elad Nava

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answered Jun 09 '14 at 07:30

Aown Raza

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8

It would be nice if you provided some sort of explanation along with your code. – Michael Jun 09 '14 at 07:50
2

simple and straightforward, worked for me too, thank you so much – eyadMhanna Sep 16 '15 at 08:37
in Android not work into -> adapter Recycle - > ViewHolder - >view.setOnClickListener – Oct 05 '15 at 23:52
3

Added an explanation. – Elad Nava Nov 09 '15 at 21:43
`myLooper` the naming is really funny. – Shawn May 03 '16 at 00:40

score 7 · Answer 2 · answered May 24 '16 at 08:03

7

Instead of just calling Looper.prepare();, first check if Looper does not already exist for your Thread, if not, call that function. Like this:

if (Looper.myLooper()==null)
    Looper.prepare();

answered May 24 '16 at 08:03

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java.lang.RuntimeException: Only one Looper may be created per thread

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